Positive electrode active material and secondary battery

Abstract

Lithium-ion secondary battery comprising: a positive electrode comprising a positive electrode active material particle and a coating film covering the positive electrode active material particle, wherein the positive electrode active material particle comprises magnesium, titanium, fluorine and lithium cobaltate, wherein the positive electrode active material particle has a region comprising a rock salt crystal structure, wherein the coating film is in contact with the region comprising the rock salt crystal structure, wherein the region comprising the rock salt crystal structure comprises cobalt, magnesium oxide, titanium and fluorine, wherein in a part of the magnesium oxide contained in the region comprising the rock salt crystal structure, fluorine is bonded to magnesium as a substitute for oxygen, and wherein the region comprising the rock salt crystal structure comprises a solid solution comprising cobalt oxide and magnesium oxide.

Description

Technical area

[0001] One embodiment of the present invention relates to an object. The present invention relates to a machine, a product, or a composition. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, an energy storage device, a lighting device, and an electrical device. More specifically, one embodiment of the present invention relates to a positive electrode active material usable in a secondary battery, a secondary battery, and an electrical device including a secondary battery.

[0002] The term "energy storage device" in this specification is a collective term that describes elements and devices with an energy storage function. For example, the category of energy storage device includes a secondary battery, such as a lithium-ion secondary battery (also referred to as a secondary battery), a lithium-ion capacitor, and an electric double-layer capacitor.

[0003] It should be noted that in this specification, electrical devices refer to all devices that include energy storage devices, and that electro-optical devices that include energy storage devices, information terminal devices that include energy storage devices, and the like are all electrical devices. State of the art

[0004] In recent years, various energy storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, have been intensively developed. In particular, in line with the development of the semiconductor industry, the demand for high-output, high-energy-density lithium-ion secondary batteries has increased sharply for portable information terminals such as mobile phones, smartphones, tablets, and laptop computers; portable music players, digital cameras; medical devices; and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs). Lithium-ion secondary batteries are essential rechargeable energy sources for today's information society.

[0005] The performance required for lithium-ion secondary batteries includes increased energy density, improved cycle performance, safe operation in a variety of environments, and longer-term reliability.

[0006] Thus, the improvement of a positive electrode active material has been investigated to increase the cycle performance and capacity of the lithium-ion secondary battery (Patent Document 1 and Patent Document 2). [Reference][Patent Documents] [Patent Document 1] Japanese Patent Laid-Open No. 2012-018914 [Patent Document 2] Japanese Patent Laid-Open No. 2015-201432 Disclosure of the invention

[0007] The development of lithium-ion secondary batteries and positive electrode active materials used therein has room for improvement in terms of charge and discharge characteristics, cycle characteristics, reliability, safety, cost, and the like.

[0008] An object of one embodiment of the present invention is to provide a positive electrode active material that suppresses a reduction in capacity due to charge and discharge cycles when used in a lithium-ion secondary battery. Another object of one embodiment of the present invention is to provide a high-capacity secondary battery. Another object of one embodiment of the present invention is to provide a secondary battery with excellent charge and discharge characteristics. Another object of one embodiment of the present invention is to provide a highly safe or highly reliable secondary battery.

[0009] Another object of an embodiment of the present invention is to provide a novel material, a novel active material particle, a novel secondary battery.

[0010] It should be noted that the descriptions of these objects do not preclude the existence of other objects. Not all objects need to be fulfilled in one embodiment of the present invention. Further objects may be derived from the explanation of the description, the drawings, and the claims.

[0011] To achieve the above objects, in one embodiment of the present invention, two types of regions other than a region inside the positive electrode active material are provided in a surface portion of the positive electrode active material. It is preferable that the inner region contains a non-stoichiometric compound, and the outer region contains a stoichiometric compound.

[0012] Furthermore, it is preferred that the inner region contains titanium and the outer region contains magnesium. Furthermore, these two types of regions can overlap.

[0013] Furthermore, it is preferable that the inner region is formed by a coating process such as a sol-gel method and the outer region is formed by segregation due to heating.

[0014] One embodiment of the present invention is a positive electrode active material comprising a first region, a second region, and a third region. The first region is present within the positive electrode active material. The second region and the third region are present in a surface portion of the positive electrode active material. The third region is present in a region closer to a surface of the positive electrode active material than the second region. The first region contains an oxide of lithium and a first transition metal and has a layered rock-salt crystal structure. The second region contains a non-stoichiometric compound containing an oxide of a second transition metal, and the non-stoichiometric compound has a rock-salt crystal structure.The third region contains a compound of representative elements and the compound of representative elements has a rock salt crystal structure.

[0015] In the above structure, it is preferred that the first transition metal is cobalt, the second transition metal is titanium, and the compound of representative elements is magnesium oxide.

[0016] In the above structure, the third region may contain fluorine. Furthermore, the second region and the third region may each contain cobalt.

[0017] In the above structure, it is preferable that crystal orientations of the first region and the second region are partially aligned with each other and crystal orientations of the second region and the third region are partially aligned with each other.

[0018] In the above structure, a degree of mismatch between a (1-1-4) plane of the layered rock-salt crystal structure in the first region or a plane orthogonal to the (1-1-4) plane and a {100} plane of the rock-salt crystal structure in the second region is preferably less than or equal to 0.12, and a degree of mismatch between the {100} plane of the rock-salt crystal structure in the second region and a {100} plane of the rock-salt crystal structure in the third region is preferably less than or equal to 0.12.

[0019] Another embodiment of the present invention is a positive electrode active material containing lithium, titanium, cobalt, magnesium, oxygen, and fluorine. When the concentration of cobalt present in a surface portion of the positive electrode active material measured by X-ray photoelectron spectroscopy is 1, the concentration of titanium is greater than or equal to 0.05 and less than or equal to 0.4, the concentration of magnesium is greater than or equal to 0.4 and less than or equal to 1.5, and the concentration of fluorine is greater than or equal to 0.05 and less than or equal to 1.5.

[0020] Another embodiment of the present disclosure is a method for forming a positive electrode active material, comprising: a step of mixing a lithium source, a cobalt source, a magnesium source, and a fluorine source; a step of heating the mixture of the lithium source, the cobalt source, the magnesium source, and the fluorine source at 800°C or higher and 1100°C or lower for 2 hours or longer and 20 hours or shorter to obtain particles containing lithium, cobalt, magnesium, oxygen, and fluorine; a step of dissolving titanium alkoxide in alcohol; a step of mixing the particles containing lithium, cobalt, magnesium, oxygen, and fluorine into the alcohol solution of the titanium alkoxide and stirring the mixed solution in an atmosphere containing water vapor; a step of collecting a precipitate from the mixed solution;and a step of heating the collected precipitate at 500 °C or higher and 1200 °C or lower in an atmosphere containing oxygen under a condition where the retention time is 50 hours or shorter.;

[0021] In the above forming method, a ratio of the number of lithium atoms in the lithium source to the number of cobalt atoms in the cobalt source is preferably greater than or equal to 1.00 and less than 1.07.

[0022] In the above forming method, a ratio between the number of magnesium atoms in the magnesium source and the number of fluorine atoms in the fluorine source is preferably Mg:F = 1:x (1.5 ≤ x ≤ 4).

[0023] In the above forming method, the number of magnesium atoms in the magnesium source is preferably greater than or equal to 0.5 atomic% and less than or equal to 1.5 atomic% of the number of cobalt atoms in the cobalt source.

[0024] In the above forming method, lithium carbonate, cobalt oxide, magnesium oxide and lithium fluoride can be used as lithium source, cobalt source, magnesium source and fluorine source, respectively.

[0025] If the surface of the positive electrode active material is covered with a coating film to protect the protruding crystal structure, a decrease in capacity due to charge and discharge cycles can be suppressed. A coating film containing carbon (a film containing a graphene compound) or a coating film containing lithium or a decomposition product of an electrolyte solution is used as the coating film covering the surface of the positive electrode active material.

[0026] In particular, it is preferable to obtain a powder in which the surface of the positive electrode active material has been coated with graphene oxide using a spray-drying device. The spray-drying device is a production device that uses a spray-drying method in which a dispersion medium is removed by supplying a hot air stream to a suspension.

[0027] When charging and discharging cycles are repeated, deformation of the positive electrode active material particles, such as cracking or damage, may occur. Such deformation is said to expose a new surface of the positive electrode active material, and the surface comes into contact with an electrolyte solution, causing a decomposition reaction or the like, thereby deteriorating the cycle characteristics and the charging and discharging characteristics of the secondary battery.

[0028] Thus, a coating film is preferably provided to prevent deformation of the particles of the positive electrode active materials, such as cracking or damage.

[0029] However, when the suspension is formed and stirred by a planetary centrifugal mixer (rotary and revolutionary mixer) to coat the surface of the positive electrode active material, whose weight per unit volume is large, with graphene oxide, whose weight is relatively small, the coating is insufficient.

[0030] Accordingly, to coat the surfaces of the positive electrode active material particles with graphene oxide, a method is preferably used in which graphene oxide and a polar solvent (such as water) are mixed, ultrasonic treatment is performed, the positive electrode active material particles are mixed therein to form a suspension, and a dried powder is prepared using a spray dryer. The dried powder thus produced is sometimes referred to as a composite.

[0031] The size of a drop of a spray liquid sprayed from a nozzle of the spray drying device depends on a nozzle diameter.

[0032] If the particle diameter is smaller than the nozzle diameter, a drop of the spray liquid sprayed from the nozzle will contain a multitude of particles. When observing the particle surface after drying under the condition where the largest particle size is smaller than the nozzle diameter, there are some sections where the surface is coated with graphene oxide, but the coating is insufficient.

[0033] The nozzle diameter of the spray-drying device is preferably substantially equal to the largest particle size of the active material, as the coverage of the active material can be improved. Furthermore, the largest particle size of the positive electrode active material is preferably set to be substantially equal to the nozzle diameter when forming the positive electrode active material.

[0034] Since graphene oxide is well dispersed in water, a suspension of water and graphene oxide can be formed by stirring using ultrasonic waves. The positive electrode active material is added to the suspension, and the suspension is sprayed with a spray dryer, thereby obtaining a powder in which the surface of the positive electrode active material is coated with graphene oxide.

[0035] It should be noted that the suspension becomes more acidic as the amount of graphene oxide increases. Thus, a portion of the surface of the positive electrode active material (e.g., LiCoO2 containing Mg and F) could be etched. Then, a hydrogen ion exponent (pH) of the suspension before spraying is preferably adjusted to be approximately close to pH 7, i.e., nearly neutral, or higher than or equal to pH 8, i.e., alkaline. An aqueous LiOH solution is preferably used for pH adjustment. For example, in the case where LiCoO2 is used for the positive electrode active material and only pure water is used as the dispersion medium of the suspension, the surface of the positive electrode active material may be damaged. Thus, a mixed solution of ethanol and water is used as the dispersion medium of the suspension, which can reduce damage to the surface of the active material.

[0036] The suspension is formed in the above manner, whereby the positive electrode active material whose surface is coated with graphene oxide can be efficiently produced. When the surface is coated with graphene oxide, deformation of the particles of the positive electrode active material, such as cracking or damage, can be prevented. Even if the positive electrode active material whose surface is coated with graphene oxide is further exposed to air after formation, changes in properties or deterioration can be suppressed. Here, "after formation" refers to a period from the completion of the formation of the positive electrode active material to the start of production of the secondary battery containing the positive electrode active material, and includes storage, transportation, and the like of the positive electrode active material.In addition, when the coating film is formed, the positive electrode active material and the electrolyte solution can be prevented from being in direct contact with each other to react; thus, the secondary battery using the coating film has high reliability.

[0037] For the spray-drying method, a known apparatus can be used; for example, a countercurrent pressure-nozzle-type spray dry apparatus and a counter-cocurrent pressure-nozzle-type spray dry apparatus can be used.

[0038] It should be noted that the graphene oxide coating the surface of the active material can be reduced when used in the secondary battery. The reduced graphene oxide is sometimes referred to as "RGO." In RGO, some of the oxygen atoms remain in a state of oxygen or an atomic group containing oxygen bonded to carbon. For example, RGO includes a functional group such as an epoxy group, a carbonyl group such as a carboxyl group, or a hydroxyl group.

[0039] Another embodiment of the present invention is a secondary battery comprising a positive electrode containing the above-described positive electrode active material or the above-described positive electrode active material coated with a coating film, and a negative electrode.

[0040] The secondary battery may have a variety of shapes to match the shape of the device to be used, such as a cylindrical shape, a rectangular shape, a button cell shape, and a laminated (flat plate) shape.

[0041] According to one embodiment of the present invention, a positive electrode active material is provided that suppresses capacity reduction due to charge and discharge cycles when used in a lithium-ion secondary battery. Additionally, a secondary battery with excellent charge and discharge characteristics is provided. Furthermore, a highly safe or highly reliable secondary battery is provided. Additionally, a novel material, a novel active material particle, a novel secondary battery, or a formation method thereof is provided. Short description of the drawings

[0042] In the attached drawings: Fig. 1A to Fig. 1C show examples of a positive electrode active material; Fig. 2A and Fig. 2B shows crystal structures of a positive electrode active material; Fig. 3 shows crystal structures of a positive electrode active material; Fig. 4A-1, Fig. 4A-2, Fig. 4A-3, Fig. 4B, Fig. 4C, Fig. 4D-1 and Fig. 4D-2 show a sol-gel process; Fig. 5A to Fig. 5C represents a segregation model of elements contained in a positive electrode active material; Fig. 6A to Fig. 6D represents a segregation model of elements contained in a positive electrode active material; Fig. 7A and Fig. 7B are cross-sectional views of an active material layer containing a graphene compound as a conductive additive; Fig. 8A to Fig. 8C illustrate a method of charging a secondary battery; Fig. 9A to Fig. 9D illustrate a method of charging a secondary battery; Fig. 10 illustrates a method of discharging a secondary battery; Fig. 11A to Fig. 11C represents a button cell secondary battery; Fig. 12A to Fig. 12D represent a cylindrical secondary battery; Fig. 13A and Fig. 13B illustrates an example of a secondary battery; Fig. 14A-1, Fig. 14A-2, Fig. 14B-1 and Fig. 14B-2 are examples of secondary batteries; Fig. 15A and Fig. 15B represent examples of secondary batteries; Fig. 16 shows an example of a secondary battery; Fig. 17A to Fig. 17C represents a laminated secondary battery; Fig. 18A and Fig. 18B represent a laminated secondary battery; Fig. 19 is an external view of a secondary battery; Fig. 20 is an external view of a secondary battery; Fig. 21A to Fig. 21C illustrates a formation method of a secondary battery; Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D represent a flexible secondary battery; Fig. 23A and Fig. 23B represent a flexible secondary battery; Fig. 24A to Fig. 24H are examples of electrical devices; Fig. 25A to Fig. 25C represents an example of an electrical device; Fig. 26 shows examples of electrical devices; Fig. 27A to Fig. 27C represent examples of electrical devices; Fig. 28 is a transmission electron microscope image of a positive electrode active material of Example 1; Fig. 29A1, Fig. 29A2, Fig. 29B1, Fig. 29B2, Fig. 29C1 and Fig. 29C2 are FFT images of transmission electron microscope images of a positive electrode active material of Example 1; Fig. 30A1, Fig. 30A2, Fig. 30B1, Fig. 30B2, Fig. 30C1 and Fig. 30C2 are element distribution images of a positive electrode active material of Example 1; Fig. 31A1, Fig. 31A2, Fig. 31B1, Fig. 31B2, Fig. 31C1 and Fig. 31C2 are element distribution diagrams of a positive electrode active material of a comparative example of Example 1; Fig. 32 is a graph showing TEM-EDX line analysis results of a positive electrode active material of Example 1; Fig. 33 is a graph showing the charging and discharging characteristics of a secondary battery of Example 1; Fig. 34 is a graph showing the charging and discharging characteristics of a secondary battery of a comparative example of Example 1; Fig. 35 is a graph showing the cycle characteristics of a secondary battery of Example 1; Fig. 36 is a graph showing the cycle characteristics of a secondary battery of Example 1; Fig. 37A, Fig. 37B1, Fig. 37B2, Fig. 37C1, Fig. 37C2, Fig. 37D1, Fig. 37D2, Fig. 37E1 and Fig. 37E2 are TEM-EDX plane analysis images of a comparative sample of Example 2; Fig. 38A, Fig. 38B1, Fig. 38B2, Fig. 38C1, Fig. 38C2, Fig. 38D1, Fig. 38D2, Fig. 38E1 and Fig. 38E2 are TEM-EDX plane analysis images of a positive electrode active material of Example 2; Fig. 39A, Fig. 39B1, Fig. 39B2, Fig. 39C1, Fig. 39C2, Fig. 39D1, Fig. 39D2, Fig. 39E1 and Fig. 39E2 are TEM-EDX plane analysis images of a comparative sample of Example 2; Fig. 40A, Fig. 40B1, Fig. 40B2, Fig. 40C1, Fig. 40C2, Fig. 40D1, Fig. 40D2, Fig. 40E1 and Fig. 40E2 are TEM-EDX plane analysis images of a positive electrode active material of Example 2; Fig. 41A and Fig. 41B is a graph showing EDX spot analysis results of Example 2; Fig. 42A and Fig. 42B is a graph showing EDX spot analysis results of Example 2; Fig. 43 is a graph showing the rate characteristics of a secondary battery of Example 2; Fig. 44 is a graph showing the temperature characteristics of a secondary battery of Example 2; Fig. 45 is a graph showing the cycle characteristics of a secondary battery of Example 2; Fig. 46A and Fig. 46B is each a graph showing XPS analysis results of a positive electrode active material of Example 3; Fig. 47A and Fig. 47B are each a graph showing the cycle characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. 48 is a graph showing cycle characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. 49 is a graph showing cycle characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. 50A to Fig. 50C are each a graph showing the charging and discharging characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. 51A to Fig. 51C are SEM images of a positive electrode active material of Example 4; Fig. 52A-1, Fig. 52A-2, Fig. 52B-1, Fig. 52B-2, Fig. 52C-1 and Fig. 52C-2 are SEM-EDX images of a positive electrode active material of Example 4; Fig. 53 is a process flow diagram of Example 5; Fig. 54 illustrates a spray drying apparatus of Example 5; Fig. 55 is a TEM image showing an embodiment of the present invention of Example 5; Fig. 56 is an SEM image showing an embodiment of the present invention of Example 5; Fig. 57 is an SEM image showing a comparative example of Example 5; and Fig. 58A and Fig. 58B are cross-sectional views of an active material layer of Example 5 containing a graphene compound as a conductive additive. Best mode for carrying out the invention

[0043] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that modes and details of the present invention can be modified in various ways. Furthermore, the present invention should not be construed as limited to the description in the following embodiments.

[0044] Note that in the drawings used in this specification, the sizes, thicknesses, and the like of components such as a positive electrode, a negative electrode, an active material layer, a separator, and an outer part are exaggerated in some cases for simplicity. Therefore, the sizes of the components are not limited to the sizes shown in the drawings, nor are the size ratios between the components.

[0045] Note that in the structures of the present invention described in this specification and the like, the same portions or portions with similar functions are designated by common reference numerals in different drawings, and the descriptions thereof will not be repeated. Furthermore, the same hatching pattern is used for portions with similar functions, and in some cases, the portions are not specifically designated with reference numerals.

[0046] In this specification and the like, the Miller index is used to indicate crystal planes and orientations. In crystallography, an overbar is placed over a number in the specification that uses the Miller index; however, in this specification and the like, due to specification limitations, crystal planes and orientations are expressed by placing a minus sign (-) in front of a number instead of placing the overbar over a number. Further, a single direction showing an orientation in the crystal is represented by "[ ]", a set direction showing all equivalent orientations is represented by "< >", a single direction showing a crystal plane is represented by "( )", and a set plane having equivalent symmetry is represented by "{}".In the drawings, the crystal planes and orientations are expressed by a number with a bar, which is an original crystallographic specification. Note that 1 Å is equal to 10. -10 m is.

[0047] In this description and the like, segregation refers to a phenomenon in which a particular element (e.g., B) is unevenly distributed in a solid consisting of several elements (e.g., A, B, and C).

[0048] In this specification and the like, a layered rock-salt crystal structure contained in a composite oxide containing lithium and a transition metal refers to a crystal structure in which a rock-salt ion array in which cations and anions are alternately arranged is contained, and the lithium and the transition metal are regularly arranged to form a two-dimensional plane, allowing lithium to diffuse two-dimensionally. Note that a defect such as a cation or anion vacancy may exist. In the layered rock-salt crystal structure, strictly speaking, a lattice of a rock-salt crystal is distorted in some cases.

[0049] In this specification and the like, a rock salt crystal structure refers to a structure in which cations and anions are arranged alternately. Note that a cation or anion vacancy may exist.

[0050] The anions of a layered rock-salt crystal and the anions of a rock-salt crystal each form a cubic close-packed structure (face-centered cubic lattice structure). When a layered rock-salt crystal and a rock-salt crystal are in contact with each other, there is a crystal plane where the directions of the cubic close-packed structures composed of anions are aligned. The space group of the layered rock-salt crystal is R-3m, which is different from the space group Fm-3m of a general rock-salt crystal and the space group Fd-3m of a rock-salt crystal with simplest symmetry. Thus, the Miller index of the crystal plane that satisfies the above conditions in the layered rock-salt crystal is different from that in the rock-salt crystal.In this specification, in the layered rock salt crystal and the rock salt crystal, a state in which the directions of the cubic closest packed structures consisting of anions are aligned with each other is referred to as a state in which crystal orientations are substantially aligned with each other.

[0051] Whether the crystal orientations in two regions are aligned or not can be judged by a transmission electron microscope (TEM) image, a scanning transmission electron microscope (STEM) image, a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image, an annular brightfield scanning transmission electron microscopy (ABF-STEM) image, and the like. X-ray diffraction, electron diffraction, neutron diffraction, and the like can be used for judgment. In the TEM image and the like, the alignment of cations and anions can be observed as repetition of bright lines and dark lines.When the orientations of the cubic close-packed structures of the layered rock-salt crystal and the rock-salt crystal are aligned with each other, a state in which an angle between the repetition of bright lines and dark lines in the layered rock-salt crystal and the repetition of bright lines and dark lines in the rock-salt crystal is less than or equal to 5°, preferably less than or equal to 2.5°, is observed. Note that in the TEM image and the like, in some cases, a light element such as oxygen or fluorine is not clearly observed; however, in such a case, the alignment of the orientations can be judged by the arrangement of metal elements.

[0052] Furthermore, in this specification and the like, a state in which two-dimensional interface structures have similarity is referred to as "epitaxy." Crystal growth in which two-dimensional interface structures have similarity is referred to as "epitaxial growth." Furthermore, a state in which three-dimensional structures have similarity or orientations are crystallographically similar is referred to as "topotaxy." Therefore, in the case of topotaxy, when a part of a cross-section is observed, the orientations of crystals in two regions (e.g., a region serving as a base and a region formed by growth) are substantially aligned with each other. (Embodiment 1)[Structure of the positive electrode active material]

[0053] First, a positive electrode active material 100 which is an embodiment of the present invention will be described with reference to Fig. 1A to Fig. 1C. The positive electrode active material 100 refers to a substance containing a transition metal that can electrochemically absorb and release lithium ions. As shown in Fig. 1A, the positive electrode active material 100 includes a first region 101 located inside and a second region 102 and a third region 103 in a surface portion.

[0054] As in Fig. 1B, the second region 102 does not necessarily cover the entire first region 101. Similarly, the third region 103 does not necessarily cover the entire second region 102. Additionally, the third region 103 may be in contact with the first region 101.

[0055] The thicknesses of the second region 102 and the third region 103 may differ depending on the positions.

[0056] Furthermore, the third region 103 may be present within the positive electrode active material 100. For example, in the case where the first region 101 is a polycrystal, the third region 103 may be present near a grain boundary. Furthermore, the third region 103 may be present in a portion having crystal defects or a crack portion in or near the positive electrode active material 100. Fig. 1B, parts of grain boundaries are shown by dotted lines. In this specification and the like, crystal defects refer to defects that can be observed in a TEM image and the like, that is, a structure in which another element enters a crystal, a void, and the like. Furthermore, a crack portion refers to, for example, a crack or fracture such as a crack portion 106 formed in Fig. 1C, is formed in a particle.

[0057] Similarly, as in Fig. 1B, the second region 102 may be present within the positive electrode active material 100. For example, in the case where the first region 101 is a polycrystal, the second region 102 may be present near a grain boundary. Further, the second region 102 may be present in or near a portion having crystal defects or a cracked portion in the positive electrode active material 100. Furthermore, the third region 103 and the second region 102 may overlap within the positive electrode active material 100. <Erster Bereich 101>

[0058] The first region 101 contains a composite oxide of lithium and a first transition metal. In other words, the first region 101 contains lithium, a first transition metal, and oxygen.

[0059] The composite oxide of lithium and a first transition metal preferably has a layered rock salt crystal structure.

[0060] As the first transition metal, only cobalt can be used, cobalt and manganese can be used, or cobalt, manganese and nickel can be used.

[0061] That is, the first region 101 may contain lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which part of the cobalt is replaced by manganese, lithium nickel manganese cobalt oxide, or the like. In addition to the transition metal, the first region 101 may contain a metal other than the transition metal, such as aluminum.

[0062] The first region 101 serves as a region that particularly contributes to a charge and discharge reaction in the positive electrode active material 100. To increase the capacity of a secondary battery containing the positive electrode active material 100, the volume of the first region 101 is preferably larger than that of the second region and that of the third region.

[0063] A material having a layered rock-salt crystal structure has features such as high discharge capacity and low resistance due to lithium that can diffuse two-dimensionally, and is preferably used for the first region 101. In addition, in the case where the first region 101 has a layered rock-salt crystal structure, segregation of a representative element such as magnesium, which will be described later, tends to occur unexpectedly.

[0064] It should be noted that the first region 101 can be a single crystal or a polycrystal. For example, the first region 101 can be a polycrystal in which the average crystallite size is greater than or equal to 280 nm and less than or equal to 630 nm. In the case of a polycrystal, a grain boundary can be observed in some cases using TEM or the like. In addition, the average of the crystal grain sizes can be calculated from the XRD half-width.

[0065] The polycrystal has a clear crystal structure; thus, a two-dimensional diffusion path for lithium ions can be sufficiently ensured. In addition, a polycrystal is easy to manufacture compared to a single crystal; therefore, a polycrystal is preferably used for the first region 101.

[0066] Furthermore, the entire first region 101 does not necessarily have a layered rock salt crystal structure. For example, a portion of the first region 101 may be amorphous or have a different crystal structure. <Zweiter Bereich 102>

[0067] The second region 102 contains an oxide of a second transition metal. In other words, the second region 102 contains a second transition metal and oxygen.

[0068] A non-stoichiometric metal is preferably used as the second transition metal. In other words, the second region 102 preferably comprises a non-stoichiometric compound. For example, at least one of titanium, vanadium, manganese, iron, chromium, niobium, cobalt, zinc, zirconium, nickel, and the like can be used as the second transition metal. It should be noted that the second transition metal is preferably an element that is different from the first transition metal.

[0069] In this specification and the like, a non-stoichiometric metal refers to a metal that can exhibit a variety of valences. A non-stoichiometric compound also refers to a compound of a metal that can exhibit a variety of valences and another element.

[0070] The second region 102 preferably has a rock salt crystal structure.

[0071] The second region 102 serves as a buffer region connecting the first region 101 to the third region 103 described later. In the non-stoichiometric compound, an atomic distance can be changed in accordance with a valence change of a metal contained in the non-stoichiometric compound. In addition, a cation or anion vacancy and dislocation (also called a Magneli phase) are often formed in the non-stoichiometric compound. Thus, the second region 102, serving as a buffer region, can absorb a stress generated between the first region 101 and the third region 103.

[0072] Furthermore, the second region 102 may contain lithium in addition to the second transition metal and oxygen. For example, lithium titanate or lithium manganite may be contained. Furthermore, the second region 102 may contain a representative element contained in the third region 103, which will be described later. The second region 102 containing an element contained in the first region 101, such as lithium, and an element contained in the third region 103 is preferable because the second region 102 serves as a buffer region.

[0073] That is, the second region 102 may contain lithium titanate, titanium oxide, vanadium oxide, manganese oxide, iron oxide, copper oxide, chromium oxide, niobium oxide, cobalt oxide, zinc oxide, or the like.

[0074] Additionally, the second region 102 may contain the first transition metal. For example, the second transition metal may be present in a portion of a first transition metal site of the composite oxide comprising the first transition metal.

[0075] For example, in the case where the second transition metal is titanium, titanium may be present as titanium oxide (TiO2) or lithium titanate (LiTiO2) in the second region 102. Alternatively, in the second region 102, a portion of the first transition metal site of the composite oxide of lithium and the first transition metal may be replaced by titanium.

[0076] In addition, the second region 102 may contain fluorine.

[0077] The second region 102 preferably has a crystal structure that is the same as that of the third region 103, which will be described later. In this case, the orientations of crystals in the second region 102 and the third region 103 are likely to be aligned with each other.

[0078] The second region 102 preferably has a rock salt crystal structure; however, the entire second region 102 does not necessarily have a rock salt crystal structure. For example, the second region 102 may have a different crystal structure, such as a spinel crystal structure, an olivine crystal structure, a corundum crystal structure, or a rutile crystal structure.

[0079] Furthermore, a crystal structure may exhibit strain as long as a structure in which six oxygen atoms are adjacent to cations is maintained. Additionally, a cation vacancy may be present in a portion of the second region 102.

[0080] Furthermore, a part of the second region 102 may be amorphous.

[0081] If the thickness of the second region 102 is too small, its function as a buffer region deteriorates; however, if the thickness of the second region 102 is too large, the capacity may decrease. Thus, the second region 102 is preferably provided in a region from the surface of the positive electrode active material 100 to a depth of 20 nm, preferably a depth of 10 nm, in a depth direction. The second transition metal may have a concentration gradient. <Dritter Bereich 103>

[0082] The third region 103 contains a compound of representative elements. A compound of representative elements is a stoichiometric compound. As the compound of representative elements, a compound consisting of electrochemically stable representative elements is preferred, and at least one of magnesium oxide, calcium oxide, beryllium oxide, lithium fluoride, and sodium fluoride can be used, for example.

[0083] The third region 103 is in contact with an electrolytic solution when the positive electrode active material 100 is used in a secondary battery. Thus, for the third region 103, a material that is hardly electrochemically changed during charging and discharging and is not easily converted by contact with the electrolytic solution is preferably used. The compound of representative elements that is a stoichiometric compound and is electrochemically stable is preferably used for the third region 103. The positive electrode active material 100 includes the third region 103 in a surface portion to improve stability during charging and discharging of the secondary battery. Here, a state in which the stability of a secondary battery is high refers to a state in which the crystal structure of the composite oxide of lithium and the first transition metal contained in the first region 101 is more stable.Alternatively, it refers to a state in which a capacity change of the secondary battery is small even if charging and discharging are repeated, or to a state in which a valence change of a metal contained in the positive electrode active material 100 is suppressed even after repeated charging and discharging.

[0084] The third region 103 may contain fluorine. In the case where the third region 103 contains fluorine, fluorine may replace some anions in the compound of representative elements.

[0085] Fluorine replaces some anions in the compound of representative elements, which can improve the diffusion properties of lithium. Thus, the third region 103 is less likely to inhibit charging and discharging. Furthermore, when fluorine is present in a surface portion of a positive electrode active material particle, in some cases, corrosion resistance to hydrofluoric acid generated by decomposition of an electrolyte solution is increased.

[0086] Furthermore, the third region 103 may comprise lithium, the first transition metal and the second transition metal.

[0087] The combination of representative elements contained in the third region 103 preferably has a rock-salt crystal structure. When the third region 103 has a rock-salt crystal structure, the crystal orientations are likely to be aligned with those of the second region 102. The crystal orientations of the first region 101, the second region 102, and the third region 103 are substantially aligned with each other, allowing the second region 102 and the third region 103 to serve as a more stable coating layer.

[0088] However, the entire third region 103 does not necessarily have a rock salt crystal structure. For example, the third region 103 may have another crystal structure, such as a spinel crystal structure, an olivine crystal structure, a corundum crystal structure, or a rutile crystal structure.

[0089] Furthermore, a crystal structure may exhibit strain as long as a structure in which six oxygen atoms are adjacent to cations is maintained. Additionally, a cation vacancy may be present in a portion of the third region 103.

[0090] Furthermore, a part of the third region 103 may be amorphous.

[0091] If the thickness of the third region 103 is too small, its function of increasing stability during charging and discharging will deteriorate; however, if the thickness of the third region 103 is too large, the capacity may decrease. Therefore, the thickness of the third region 103 is preferably greater than or equal to 0.5 nm and less than or equal to 50 nm, more preferably greater than or equal to 0.5 nm and less than or equal to 2 nm.

[0092] In the case where the third region 103 contains fluorine, fluorine is preferably present in a bonding state other than magnesium fluoride (MgF2), lithium fluoride (LiF), and cobalt fluoride (CoF2). Specifically, when XPS analysis is performed near the surface of the positive electrode active material 100, a peak position of the bonding energy of fluorine is preferably higher than or equal to 682 eV and lower than or equal to 685 eV, more preferably approximately 684.3 eV. The bonding energy does not correspond to those of MgF2, LiF, and CoF2.

[0093] In this specification and the like, a peak position of the binding energy of an element in an XPS analysis refers to a binding energy value at which the maximum intensity of an energy spectrum is obtained in a range corresponding to the binding energy of the element.

[0094] Generally, when charging and discharging are repeated, a side reaction occurs in a positive electrode active material. For example, a first transition metal such as manganese, cobalt, or nickel dissolves in an electrolyte solution, oxygen is released, and a crystal structure becomes unstable, so that the positive electrode active material deteriorates. However, the positive electrode active material 100 of one embodiment of the present invention includes the second region 102 serving as a buffer region and the third region 103 being electrochemically stable. Thus, the dissolution of the first transition metal can be effectively suppressed, and the crystal structure of the composite oxide of lithium and the transition metal contained in the first region 101 can be more stable. As a result, the cycle characteristics of the secondary battery containing the positive electrode active material 100 can be significantly improved.In the case where charging and discharging is carried out at a voltage higher than 4.3 V (vs. Li / Li. + ), especially at a high voltage of 4.5 V (vs. Li / Li + ) or higher, the structure of an embodiment of the present invention is significantly effective. <Heteroepitaktisches Wachstum und Topotaxie>

[0095] The second region 102 is preferably formed by heteroepitaxial growth from the first region 101. Furthermore, the third region 103 is preferably formed by heteroepitaxial growth from the second region 102. A region formed by heteroepitaxial growth becomes a topotactic region (is topotactic), having crystal orientations that are substantially three-dimensionally aligned with those of a region serving as a base. Thus, the first region 101, the second region 102, and the third region 103 can become a topotactic region (be topotactic).

[0096] When the crystal orientations of the first region 101, the second region 102, and the third region 103 are substantially aligned with each other, the second region 102 and the third region 103 serve as a coating layer having a stable bond with the first region 101. As a result, the positive electrode active material 100 having a strong coating layer can be provided.

[0097] Since the second region 102 and the third region 103 have a stable bond with the first region 101, when the positive electrode active material 100 is used for the secondary battery, a change in the crystal structure in the first region 101 caused by charging and discharging can be effectively suppressed. Even if lithium is released from the first region 101 as a result of charging, the coating layer with a stable bond can suppress the release of cobalt and oxygen from the first region 101. Furthermore, a chemically stable material can be used for a region in contact with the electrolyte solution. Thus, a secondary battery with excellent cycle characteristics can be provided. <Grad der Diskordanz zwischen Bereichen>

[0098] To induce heteroepitaxial growth, the degree of discordance between crystals in a region serving as a base and crystals in which crystal growth is induced is important.

[0099] In this specification and the like, the degree of discordance f is defined by the following formula 1. The average of the nearest neighbor distances between oxygen and cations of the crystals in the region serving as a basis is represented by a, and the average of the natural nearest neighbor distances between anions and cations of the crystals at which crystal growth is induced is represented by b. [Formula 1] f=|b−aa|

[0100] To achieve heteroepitaxial growth, the degree of discordance f between crystals in a region serving as a base and crystals in which crystal growth is induced must be less than or equal to 0.12. To achieve more stable heteroepitaxial growth to form a layered shape, the degree of discordance f is preferably less than or equal to 0.08, more preferably less than or equal to 0.04.

[0101] Thus, materials of the first region 101 and the second region 102 are preferably selected such that the degree of discordance f between the layered rock-salt crystal structure in the first region 101 and the rock-salt crystal structure in the second region 102 is less than or equal to 0.12.

[0102] Furthermore, materials of the second region 102 and the third region 103 are preferably selected such that the degree of discordance f between the rock salt crystal structure in the second region 102 and the rock salt crystal structure in the third region 103 is less than or equal to 0.12.

[0103] Examples of materials and crystal planes of the first region 101, the second region 102, and the third region 103 that satisfy the above-described conditions are shown below: The degree of discordance f between the layered rock-salt crystal structure in the first region 101 and the rock-salt crystal structure in the second region 102 is less than or equal to 0.12; and the degree of discordance f between the rock-salt crystal structure in the second region 102 and the rock-salt crystal structure in the third region 103 is less than or equal to 0.12. <<Beispiel 1: Lithiumkobaltat, Lithiumtitanat und Magnesiumoxid> >

[0104] Show first Fig. 2A and Fig. 2B and Fig. 3 an example in which the first transition metal is cobalt, the first region 101 contains lithium cobaltate having a layered rock salt crystal structure, the second transition metal is titanium, the second region 102 contains lithium titanate having a rock salt crystal structure, and the compound of representative elements in the third region 103 is magnesium oxide having a rock salt crystal structure.

[0105] Fig. Figure 2A shows a model of a layered rock-salt crystal structure (a space group R-3mH) of lithium cobaltate (LiCoO2), a model of a rock-salt crystal structure (a space group Fd-3mZ) of lithium titanate (LiTiO2), and a model of a rock-salt crystal structure (a space group Fd-3mZ) of magnesium oxide. Fig. Figure 2A shows models, each viewed from the b-axis direction.

[0106] Out of Fig. 2A, it is not apparent that the layered rock salt crystals and the rock salt crystals lead to topotaxy. Then, here, the layered rock salt crystals are viewed from a different direction (e.g., a direction indicated by an arrow in Fig. 2A). Fig. Figure 2B shows a model of the layered rock salt crystals viewed from the <1-1-4> plane direction and models of the rock salt crystals viewed from the <100> -plane direction.

[0107] As in Fig. 2B, when the layered rock salt crystals are viewed from the <1-1-4> plane direction, the atomic arrangement of the layered rock salt crystals is very similar to that of the rock salt crystals observed from the <100> -plane direction. In addition, the nearest neighbor distances between a metal and oxygen have similar values. For example, in the layered rock-salt lithium cobaltate, the distance between Li and O is 2.089 Å, and the distance between Co and O is 1.925 Å. In the rock-salt lithium titanate, the distance between Li and O is 2.138 Å, and the distance between Ti and O is 2.051 Å. In the rock-salt magnesium oxide, the distance between Mg and O is 2.106 Å.

[0108] With reference to Fig. 3, the degree of discordance between the regions in the case where the (1-1-4) crystal plane of the layered rock-salt crystal and the {100} crystal plane of the rock-salt crystal are in contact with each other is then described.

[0109] As in Fig. As shown in Figure 3, a distance between metals across oxygen (metal-oxygen-metal distance) in a (1-1-4) crystal plane 101p (1-1-4) of lithium cobaltate having the layered rock-salt crystal structure in the first region 101 is 4.01 Å. Furthermore, a distance between metals across oxygen in a {100} crystal plane 102p {100} of lithium titanate having the rock-salt crystal structure in the second region 102 is 4.19 Å. Thus, the degree of discordance f between the crystal plane 101p (1-1-4) and the crystal plane 102p {100} is 0.04.

[0110] Additionally, the distance between metals across oxygen in a {100} crystal plane 103p {100} of magnesium oxide with the rock-salt crystal structure in the third region is 1034.21 Å. Thus, the degree of discordance f between the 102p {100} crystal plane and the 103p {100} crystal plane is 0.02.

[0111] In this way, the degree of discordance between the first region 101 and the second region 102 and the degree of discordance between the second region 102 and the third region 103 are sufficiently small; thus, the first region 101, the second region 102, and the third region 103 can be a topotaxy.

[0112] Although in Fig. 3, the degree of discordance f when the crystal plane 101p (1-1-4) in the first region 101 and the crystal plane 103p {100} in the third region 103 are in contact with each other is 0.05. That is, due to the second region 102, the degree of discordance can be small. Moreover, with the second region 102 being a non-stoichiometric transition metal oxide, the first region 101, the second region 102, and the third region 103 can be more stable topotaxy (topotactically stable). Thus, the second region 102 and the third region 103 can serve as a coating layer having a stable bond with the first region 101.

[0113] In this embodiment, the (1-1-4) plane of the layered rock-salt crystal and the {100} plane of the rock-salt crystal are in contact with each other; however, an embodiment of the present invention is not limited to this, as long as crystal planes that can be a topotaxy are in contact with each other. <<Beispiel 2: Lithiumkobaltat, Manganoxid und Calciumoxid> >

[0114] Next, an example is shown in which the first transition metal is cobalt, the first region 101 contains lithium cobaltate having a layered rock salt crystal structure, the second transition metal is manganese, the second region 102 contains manganese oxide having a rock salt crystal structure, and the compound of representative elements in the third region 103 is calcium oxide having a rock salt crystal structure.

[0115] In this case too, as in Fig. 2A and Fig. 2B and Fig. 3, when the layered rock salt crystals are viewed from the <1-1-4> plane direction, the atomic arrangement of the layered rock salt crystals in the first region 101 is very similar to those of the rock salt crystals in the second region 102 and the third region 103, which are <100> -plane direction.

[0116] The degree of discordance between the regions is described in the case where the (1-1-4) crystal plane of the layered rock-salt crystal and the {100} crystal plane of the rock-salt crystal are in contact with each other. A distance between metals via oxygen in a crystal plane (1-1-4) of lithium cobaltate having the layered rock-salt crystal structure in the first region 101 is 4.01 Å. Furthermore, a distance between metals via oxygen in a crystal plane {100} of manganese oxide having the rock-salt crystal structure in the second region 102 is 4.45 Å. Thus, the degree of discordance f between the crystal plane (1-1-4) in the first region 101 and the crystal plane {100} in the second region 102 is 0.11.

[0117] In addition, a distance between metals across oxygen in a crystal plane {100} of calcium oxide having the rock-salt crystal structure in the third region 103 is 4.82 Å. Thus, the degree of discordance f between the crystal plane {100} in the second region 102 and the crystal plane {100} in the third region 103 is 0.08.

[0118] In this way, the degree of discordance between the first region 101 and the second region 102 and the degree of discordance between the second region 102 and the third region 103 are sufficiently small; thus, the first region 101, the second region 102, and the third region 103 can be a topotaxy.

[0119] The degree of discordance f when the crystal plane (1-1-4) in the first region 101 and the crystal plane {100} in the third region 103 are in contact with each other is 0.20; thus, heteroepitaxial growth is difficult to achieve. That is, due to the second region 102, heteroepitaxial growth can be achieved from the first region to the third region. Thus, the second region 102 and the third region 103 can serve as a coating layer having a stable bond with the first region 101. <<Beispiel 3: Lithium-Nickel-Mangan-Kobaltoxid, Manganoxid und Calciumoxid> >

[0120] Next, an example is shown in which the first transition metals are nickel, manganese and cobalt, the first region 101 lithium nickel manganese cobalt oxide (LiNi 0,33 Co 0,33 Mn 0,33O2) having a layered rock salt crystal structure, the second transition metal is manganese, the second region 102 contains manganese oxide having a rock salt crystal structure, and the compound of representative elements in the third region 103 is calcium oxide having a rock salt crystal structure.

[0121] In this case too, as in Fig. 2A and Fig. 2B and Fig. 3, when the layered rock salt crystals are viewed from the <1-1-4> plane direction, the atomic arrangement of the layered rock salt crystals is very similar to that of the rock salt crystals formed by the <100> -plane direction. The degree of discordance between the regions is described in the case where the (1-1-4) crystal plane of the layered rock-salt crystal and the {100} crystal plane of the rock-salt crystal are in contact with each other.

[0122] A distance between metals across oxygen in a crystal plane (1-1-4) of lithium nickel manganese cobalt oxide having the layered rock-salt crystal structure in the first region 101 is 4.07 Å. Furthermore, a distance between metals across oxygen in a crystal plane {100} of manganese oxide having the rock-salt crystal structure in the second region 102 is 4.45 Å. Thus, the degree of discordance f between the crystal plane (1-1-4) in the first region 101 and the crystal plane {100} in the second region 102 is 0.09.

[0123] In addition, a distance between metals across oxygen in a crystal plane {100} of calcium oxide having the rock-salt crystal structure in the third region 103 is 4.82 Å. Thus, the degree of discordance f between the crystal plane {100} in the second region 102 and the crystal plane {100} in the third region 103 is 0.08.

[0124] In this way, the degree of discordance between the first region 101 and the second region 102 and the degree of discordance between the second region 102 and the third region 103 are sufficiently small; thus, the first region 101, the second region 102, and the third region 103 can be a topotaxy.

[0125] The degree of discordance f when the crystal plane (1-1-4) in the first region 101 and the crystal plane {100} in the third region 103 are in contact with each other is 0.18; thus, it is difficult to induce heteroepitaxial growth. That is, by providing the second region 102, heteroepitaxial growth can be induced from the first region to the third region. Thus, the second region 102 and the third region 103 can serve as a coating layer having a stable bond with the first region 101. <Grenzen zwischen Bereichen>

[0126] As described above, the first region 101, the second region 102, and the third region 103 have different compositions. The element contained in each region has a concentration gradient in some cases. For example, the second transition metal may have a concentration gradient in the second region 102. In addition, the third region 103 may have a concentration gradient of a representative element, since a representative element is preferably segregated in the third region 103, as described later. Therefore, the boundaries between the regions are not clear in some cases.

[0127] The difference in the compositions of the first region 101, the second region 102, and the third region 103 can be observed using a TEM image, a STEM image, a fast Fourier transform (FFT) analysis, energy dispersive X-ray spectrometry (EDX), a depth-direction analysis by time-of-flight secondary ion mass spectrometry (ToF-SIMS), an X-ray photoelectron spectroscopy (XPS), an Auger electron spectroscopy, a thermal desorption spectroscopy (TDS), or the like.

[0128] For example, in the TEM image and the STEM image, a difference between constituent elements is observed as a difference in brightness; thus, a difference between constituent elements of the first region 101, the second region 102, and the third region 103 can be observed. Furthermore, in the EDX plane analysis (e.g., element distribution), it can also be observed that the first region 101, the second region 102, and the third region 103 contain different elements.

[0129] By line analysis of EDX and analysis in the depth direction using ToF-SIMS, a concentration peak of each element contained in the first region 101, the second region 102, and the third region 103 can be detected.

[0130] However, clear boundaries between the first region 101, the second region 102 and the third region 103 are not necessarily observed by the analyses.

[0131] In this specification and the like, the third region 103 present in a surface portion of the positive electrode active material 100 refers to a region from the surface of the positive electrode active material 100 to a region where a concentration of a representative element, such as magnesium, detected by depth-direction analysis is 1 / 5 of a peak. As the depth-direction analysis, the line analysis of EDX, depth-direction analysis using ToF-SIMS, or the like described above can be used.

[0132] Further, a peak of a concentration of a representative element is preferably in a range from the surface of the positive electrode active material 100 to a depth of 3 nm toward the center, more preferably to a depth of 1 nm, and even more preferably to a depth of 0.5 nm.

[0133] Although the depth at which the concentration of the representative element reaches 1 / 5 of the peak varies depending on the manufacturing method, in the case of a manufacturing method described later, the depth is approximately 2 nm to 5 nm from the surface of the positive electrode active material.

[0134] The third region 103, which exists within the first region 101 in the vicinity of a grain boundary, a crystal defect, or the like, also refers to a region in which a concentration of a representative element detected by analysis in the depth direction is higher than or equal to 1 / 5 of a peak.

[0135] A distribution of fluorine in the positive electrode active material 100 preferably overlaps with a distribution of the representative element. Thus, fluorine also has a concentration gradient, and a peak of fluorine concentration preferably lies in a range from the surface of the positive electrode active material 100 to a depth of 3 nm toward the center, more preferably to a depth of 1 nm, and even more preferably to a depth of 0.5 nm.

[0136] In this specification and the like, the second region 102 present in a surface portion of the positive electrode active material 100 refers to a region where a concentration of the second transition metal detected by analysis in the depth direction is higher than or equal to 1 / 2 of a peak. The second region 102 present within the first region 101 near a grain boundary, a crystal defect, or the like also refers to a region where a concentration of the second transition metal detected by analysis in the depth direction is higher than or equal to 1 / 2 of a peak. As the analysis method, the line analysis of EDX, a depth direction analysis using ToF-SIMS, or the like described above can be used.

[0137] Thus, in some cases, the third region 103 and the second region 102 overlap. Note that the third region 103 is preferably present in a region closer to the surface of the positive electrode active material particle than the second region 102. In addition, the peak of the concentration of the representative element is preferably present in a region closer to the surface of the positive electrode active material particle than the peak of the concentration of the second transition metal.

[0138] The peak of the second transition metal is preferably in a range from a depth of 0.2 nm or more to a depth of 10 nm or less from the surface of the positive electrode active material 100 toward the center, more preferably in a range from a depth of 0.5 nm or more to a depth of 3 nm or less.

[0139] The measurement range in XPS extends from the surface of the positive electrode active material particle 100 to a region at a depth of approximately 5 nm. Thus, the concentration of an element present at a depth of approximately 5 nm from the surface can be quantitatively analyzed. Thus, the concentration of elements in the third region 103 and the second region 102 present at a depth of approximately 5 nm from the surface can be quantitatively analyzed.

[0140] When the surface of the positive electrode active material 100 is subjected to XPS analysis and the concentration of the first transition metal is defined as 1, a relative value of the concentration of the second transition metal is preferably greater than or equal to 0.05 and less than or equal to 0.4, more preferably greater than or equal to 0.1 and less than or equal to 0.3. In addition, a relative value of the concentration of the representative element is preferably greater than or equal to 0.4 and less than or equal to 1.5, more preferably greater than or equal to 0.45 and less than or equal to 1.00. Further, a relative value of the fluorine concentration is preferably greater than or equal to 0.05 and less than or equal to 1.5, more preferably greater than or equal to 0.3 and less than or equal to 1.00.

[0141] It should be noted that, as described above, elements contained in the first region 101, the second region 102, and the third region 103 may each have a concentration gradient; thus, the first region 101 may contain the element in the second region 102 or the third region 103, such as fluorine. Similarly, the third region 103 may contain the element in the first region 101 or the second region 102. Additionally, the first region 101, the second region 102, and the third region 103 may each contain a different element, such as carbon, sulfur, silicon, sodium, calcium, chlorine, or zirconium. [particle diameter]

[0142] If the particle diameter of the positive electrode active material 100 is too large, the diffusion of lithium is difficult, whereas if the particle diameter is too small, it is difficult to maintain a crystal structure described later. Thus, D50 (also referred to as the average diameter) is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 70 μm or less. In the case where the coating film is formed on the surface of the positive electrode active material 100 with a spray-drying device in a later step, it is preferable that the nozzle diameter and the maximum particle diameter of the positive electrode active material 100 are substantially the same. If the particle diameter is less than 5 μm and a spray-drying device with a nozzle diameter of 20 μm is used, secondary particles are collectively covered, resulting in a reduction in the covering ability.

[0143] To increase the density of the positive electrode active material layer, it is effective to mix large particles (the longest section measures approximately 20 µm or more and 40 µm or less) and small particles (the longest section measures approximately 1 µm), and fill the spaces between the large particles with small particles. Therefore, two peaks of the particle size distribution may occur.

[0144] The particle size of the positive electrode active material is influenced not only by the particle sizes of the starting materials but also by a ratio between lithium and the first transition metal (hereinafter expressed as a ratio of Li to the first transition metal) contained in the starting material.

[0145] In the case where the particle size of the starting material is small, grain growth must be induced at the time of baking so that the grain size of the positive electrode active material is in the preferable range described above.

[0146] To promote grain growth during baking, it is effective to set the ratio of Li to the first transition metal of the starting material to greater than 1, that is, to slightly increase the amount of lithium. For example, when the ratio of Li to the first transition metal is approximately 1.06, a positive electrode active material in which D50 is greater than or equal to 15 μm is easily obtained. Note that, as described later, lithium may be lost to the outside of a system during the formation process of the positive electrode active material; thus, in some cases, the ratio between lithium and the first transition metal of the resulting positive electrode active material does not match the ratio between lithium and the first transition metal of the starting material.

[0147] However, if the amount of lithium is too large to keep the particle size within the preferred range, the capacity retention rate of a secondary battery containing the positive electrode active material may be reduced.

[0148] Subsequently, the inventors of the present invention found that with the second region 102 containing the second transition metal in the surface portion, the particle size can be in the preferred range by controlling the ratio of Li to the first transition metal, and a positive electrode active material having a high capacity retention rate can be formed.

[0149] In the positive electrode active material of one embodiment of the present invention comprising a region containing the second transition metal in the surface portion, the ratio of Li to the first transition metal in the starting material is preferably greater than or equal to 1.00 and less than or equal to 1.07, more preferably greater than or equal to 1.03 and less than or equal to 1.06. [Training of the second area]

[0150] The second region 102 may be formed by coating particles of the composite oxide of lithium and the first transition metal with a material containing the second transition metal.

[0151] As a coating method for the material containing the second transition metal, a liquid-phase method such as a sol-gel method, a solid-phase method, a sputtering method, an evaporation method, a chemical vapor deposition (CVD) method, a pulsed laser deposition (PLD) method, or the like can be used. In this embodiment, the case of using the sol-gel method, which can be performed with uniform coverage under atmospheric pressure, will be described. <sol-gel-verfahren>

[0152] A method of forming a material containing the second transition metal using a sol-gel method is described with reference to Fig. 4A-1, Fig. 4A-2, Fig. 4A-3, Fig. 4B, Fig. 4C, Fig. 4D-1 and Fig. 4D-2 described.

[0153] First, an alkoxide of the second transition metal is dissolved in alcohol.

[0154] Fig. Figure 4A-1 shows a general formula of the alkoxide of the second transition metal. In the formula of Fig. In 4A-1, M2 denotes the alkoxide of the second transition metal. R represents an alkyl group having 1 to 18 carbon atoms or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Although Fig. While Figure 4A-1 shows the general formula in which the second transition metal has a valence of 4, one embodiment of the present invention is not limited thereto. The second transition metal may have a valence of 2, a valence of 3, a valence of 5, a valence of 6, or a valence of 7. In this case, the alkoxide of the second transition metal includes an alkoxy group corresponding to the valence of the second transition metal.

[0155] Fig. Figure 4A-2 shows a general formula of the titanium alkoxide used when titanium is used as the second transition metal. R in Fig. 4A-2 represents an alkyl group having 1 to 18 carbon atoms or a substituted or unsubstituted aryl group having 6 to 13 carbon atoms.

[0156] As the titanium alkoxide, tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium (also called tetraisopropyl orthotitanate, titanium(IV) isopropoxide, titanium(IV) tetraisopropoxide, TTIP and the like), tetra-n-butoxytitanium, tetra-i-butoxytitanium, tetra-sec-butoxytitanium, tetra-t-butoxytitanium or the like can be used.

[0157] Fig. Figure 4A-3 shows a chemical formula of titanium(IV) isopropoxide (TTIP), which is described in a subsequent formation process and is a type of titanium alkoxide.

[0158] As a solvent in which the alkoxide of the second transition metal is dissolved, an alcohol such as methanol, ethanol, propanol, 2-propanol, butanol or 2-butanol is preferably used.

[0159] Next, particles of a composite oxide of lithium, a transition metal, magnesium, and fluorine are mixed into the alcohol solution of the alkoxide of the second transition metal and stirred in an atmosphere containing water vapor.

[0160] When the solution is exposed to an atmosphere containing H2O, hydrolysis of water and an alkoxide of the second transition metal occurs as in Fig. 4B. Then, as shown in Fig. 4C, a dehydration condensation or dehydration condensation between the products of Fig. 4B. If the hydrolysis of Fig. 4B and the condensation reaction of Fig. 4C, a sol of an oxide of the second transition metal is produced. This reaction occurs as in Fig. 4D-1 and Fig. 4D-2, also occurs in a particle 110 of the composite oxide, and a layer containing the second transition metal is formed on the surface of the particle 110.

[0161] Particle 110 is then collected and the alcohol is evaporated. The details of the formation process will be described later.

[0162] Note that in this embodiment, an example is described in which the particles of the composite oxide of lithium, the first transition metal, the representative element, and fluorine are coated with the material containing the second transition metal before the particles are applied to a positive electrode current collector; however, an embodiment of the present invention is not limited to this. After the positive electrode active material layer containing the particles of the composite oxide of lithium, the first transition metal, the representative element, and fluorine is formed on the positive electrode current collector, both the positive electrode current collector and the positive electrode active material layer may be immersed in an alkoxide solution of the second transition metal to be coated with the material containing the second transition metal. [Segregation of the third area]

[0163] The third region 103 can be formed by a sputtering method, a solid-phase method, a liquid-phase method such as a sol-gel method, or the like. However, the present inventors have found that when a source of a representative element such as magnesium and a fluorine source are mixed with a material of the first region 101 and then the mixture is heated, the representative element is segregated at a surface portion of the positive electrode active material particle to form the third region 103. In addition, they have found that with the third region 103 formed in this way, the positive electrode active material 100 has excellent cycling characteristics.

[0164] In the case where the third region 103 is formed by heating as described above, the heating is preferably performed after the composite oxide particle has been coated with the material containing the second transition metal. This is because, even after the particle has been coated with the material containing the second transition metal, the representative element, such as magnesium, is unexpectedly segregated on the surface of the particle when heating is performed.

[0165] Segregation models of the representative element are presented with reference to Fig. 5A to Fig. 5C and Fig. 6A to Fig. 6D. It is likely that the segregation model of the representative element, such as magnesium, is slightly different depending on the ratio between lithium and the first transition metal contained in a starting material. Then, a segregation model in which the ratio of Li to the first transition metal in the starting material is less than 1.03, that is, the amount of lithium is small, is described with reference to Fig. 5A to Fig. 5C. In addition, a segregation model in which the ratio of Li to the first transition metal in the starting material is greater than or equal to 1.03, ie, the amount of lithium is large, is described with reference to Fig. 6A to Fig. 6D. In these segregation models in Fig. 5A to Fig. 5C and Fig. 6A to Fig. 6D, the first transition metal is cobalt, the second transition metal is titanium and the representative element is magnesium.

[0166] Fig. Figure 5A shows a model diagram of the surface environment of the particle 110 of the composite oxide containing lithium, cobalt, magnesium, and fluorine, which is formed at a Li to Co ratio in the starting material of less than 1.03. A region 111 in the drawings contains lithium, cobalt, magnesium, and fluorine, and lithium cobaltate (LiCoO2) is a main component of the region 111. Lithium cobaltate has a layered rock salt structure.

[0167] It is well known that when synthesizing particles of the composite oxide containing lithium, cobalt, magnesium, and fluorine, lithium partially moves out of a system (a particle on which lithium is formed). This is due to lithium volatilization at the time of baking, lithium elution at the time of mixing the starting material in a solvent, and the like. Thus, the ratio of Li to Co in the particle 110 of the composite oxide containing lithium, cobalt, magnesium, and fluorine becomes smaller than the ratio of Li to Co in the starting material in some cases.

[0168] When the ratio of Li to Co in the starting material is less than 1.03, lithium is released from the lithium cobaltate on the surface of the particle 110 and cobalt oxide is easily generated. Thus, as shown in Fig. 5A, the surface of the particle 110 of the composite oxide is in some cases covered with a cobalt oxide (CoO) layer 114.

[0169] The cobalt oxide has a rock salt crystal structure. Thus, in the particle 110 Fig. 5A, the cobalt oxide layer 114 having a rock salt crystal structure is provided in some cases over and in contact with the region 111 containing lithium cobaltate having a layered rock salt crystal structure.

[0170] The particle 110 is coated with a titanium-containing material by a sol-gel method or the like. Fig. Figure 5B illustrates a state in which the particle 110 is coated with a titanium-containing layer 112 by a sol-gel process. In the stage of Fig. 5B, the titanium-containing layer 112 is a gel of titanium oxide; thus, the crystallinity is low.

[0171] Next, the particle 110 coated with the titanium-containing layer 112 is heated. Although the details of the heating conditions will be described later, for example, Fig. 5C illustrates a state in which the particle 110 is heated in an oxygen atmosphere at 800°C for two hours to form the positive electrode active material 100, which is an embodiment of the present invention. Upon heating, titanium in the titanium-containing layer 112 diffuses into the interior of the particle 110. At the same time, magnesium and fluorine contained in the region 111 are segregated to the surface of the particle 110.

[0172] As described above, cobalt oxide with a rock salt structure is present on the surface of particle 110. Furthermore, magnesium oxide also has a rock salt crystal structure. Thus, it is likely that magnesium is more stable in the state where it exists as magnesium oxide on the surface of particle 110 than in the state where it exists inside particle 110. This may be the reason why magnesium is segregated on the surface of particle 110 when particle 110 is heated.

[0173] In addition, fluorine contained in the starting material is believed to promote the segregation of magnesium.

[0174] Fluorine has a higher electronegativity than oxygen. Therefore, even in a stable compound such as magnesium oxide, when fluorine is added, an unequal charge distribution is likely to occur and a bond between magnesium and oxygen is weakened. Furthermore, oxygen is likely to be replaced by fluorine in the magnesium oxide, causing magnesium to move slightly near the substituted fluorine.

[0175] Furthermore, this can also be described by a phenomenon in which the melting point of a mixture decreases. When magnesium oxide (melting point: 2852 °C) and lithium fluoride (melting point: 848 °C) are added simultaneously, the melting point of magnesium oxide decreases. It is believed that the lowering of the melting point causes magnesium to move slightly during heating, and segregation of magnesium occurs easily.

[0176] Finally, the third region 103 becomes a solid solution of cobalt oxide and magnesium oxide, exhibiting a rock salt crystal structure. In addition, fluorine likely replaces some of the oxygen contained in the cobalt oxide and magnesium oxide.

[0177] Cobalt sites of lithium cobaltate replace part of the diffused titanium, and lithium titanate replaces another part of the diffused titanium. After heating, the second region 102 contains lithium titanate with a rock salt crystal structure.

[0178] The first region 101 contains, after heating, lithium cobaltate with a layered rock salt crystal structure.

[0179] Next, the case where the ratio of Li to Co in the starting material is greater than or equal to 1.03 will be discussed with reference to Fig. 6A to Fig. 6D described. Fig. Figure 6A illustrates a model diagram of the environment of the surface of the particle 120 of the composite oxide containing lithium, cobalt, magnesium, and fluorine, formed in the starting material at a Li to Co ratio of greater than or equal to 1.03. A region 121 in the drawings contains lithium, cobalt, magnesium, and fluorine.

[0180] Since the particle 120 in Fig. 6A contains a sufficient amount of lithium, even if lithium is released from the particle 120 at the time of baking the particle 120 of the composite oxide of lithium, cobalt, magnesium, and fluorine or the like, lithium diffuses from the interior of the particle 120 to the surface thereof to compensate for this; as a result, a cobalt oxide layer is not easily formed on the surface.

[0181] Fig. Figure 6B shows a state in which the particle 120 is in Fig. 6A is coated with a titanium-containing layer 122 by a sol-gel process. In the stage of Fig. 6B, the titanium-containing layer 122 is a gel of titanium oxide; thus, the crystallinity is low.

[0182] Fig. Figure 6C shows the state in which the particle 120 coated with the titanium-containing layer 122 is in Fig. 6B begins to heat up. Upon heating, titanium in the titanium-containing layer 122 diffuses into the interior of the particle 110. The diffused titanium bonds to the lithium contained in the region 121 to become lithium titanate, and a layer 125 containing the lithium titanate is formed.

[0183] Since lithium is bonded to titanium to form lithium titanate, the amount of lithium on the surface of particle 120 is relatively insufficient. Therefore, it is likely that, as in Fig. 6C, a cobalt oxide layer 124 is temporarily formed on the surface of the particle 120.

[0184] Fig. 6D represents the state in which heating in the state of Fig. 6C is sufficient to form the positive electrode active material 100, which is an embodiment of the present invention. Since the cobalt oxide layer 124 having a rock salt crystal structure is present on the surface, it is assumed that magnesium is more stable in the state in which it exists as magnesium oxide on the surface of the particle 120 than in the state in which it exists inside the particle 120. As in the case of Fig. 5A to Fig. As shown in Figure 5C, fluorine promotes the segregation of magnesium.

[0185] As in Fig. 6D, magnesium and fluorine contained in the region 121 are thus segregated together with the cobalt oxide on the surface to form the third region 103.

[0186] In this way, the positive electrode active material 100 is formed, which includes the third region 103 containing magnesium oxide and cobalt oxide, the second region 102 containing lithium titanate, and the first region 101 containing lithium cobaltate.

[0187] Note that in the case where the representative element is segregated by heating, if the composite oxide containing lithium and the first transition metal and contained in the first region 101 is a polycrystal or has crystal defects, the representative element may be segregated not only in the surface portion but also near a grain boundary of the composite oxide containing lithium and the first transition metal or near crystal defects thereof. The representative element segregated near a grain boundary or near crystal defects can contribute to further improving the stability of the crystal structure of the composite oxide containing lithium and the first transition metal and contained in the first region 101.

[0188] When the composite oxide containing lithium and the first transition metal contained in the first region 101 has a crack portion, the representative element is also segregated in the crack portion by heating. In addition, not only the representative element but also the second transition metal can be segregated. The crack portion is in contact with the electrolyte solution like the surface of the particle. Thus, the representative element and the second transition metal are segregated in the crack portion, and the third region 103 and the second region 102 are formed, whereby a chemically stable material can be used for the region in contact with the electrolyte solution. As a result, a secondary battery with excellent cycle characteristics can be provided.

[0189] The ratio between a representative element (T) and fluorine (F) in a starting material is preferably in a range of T:F = 1:x (1.5 ≤ x ≤ 4) (atomic ratio), as segregation of the representative element effectively occurs. The ratio between T and F is more preferably approximately 1:2 (atomic ratio).

[0190] Since the third region 103 formed by segregation is formed by epitaxial growth, the orientations of crystals in the second region 102 and the third region 103 are partially and substantially aligned with each other in some cases. That is, the second region 102 and the third region 103 become topotaxy in some cases. When the orientations of crystals in the second region 102 and the third region 103 are substantially aligned with each other, these regions can serve as a more advantageous coating layer.

[0191] However, not all representative elements, such as magnesium, added as a raw material need to be segregated in the third region 103. For example, the first region 101 may contain a small amount of a representative element, such as magnesium. <Vierter Bereich 104>

[0192] As in Fig. 1C, the positive electrode active material 100 may further include a fourth region 104 on the third region 103. Further, when the positive electrode active material 100 includes a defect such as a crack portion 106, the fourth region 104 may be provided to be embedded in the defect such as the crack portion 106.

[0193] The fourth region 104 contains some elements contained in the second region 102 and the third region 103. For example, the fourth region 104 contains the second transition metal and the representative element.

[0194] The fourth region 104 may have a protrusion, a stripe shape, or a layered shape. The fourth region 104 is formed from the second transition metals and representative elements contained in the starting material, using the second transition metal and the representative element that are not contained in the second region 102 or the third region 103, respectively. That is, with the fourth region 104, the amount of the second transition metal and the representative element contained in the second region 102 and the third region 103 can be maintained within an appropriate range, and the crystal structures of the second region 102 and the third region 103 can be stabilized in some cases. Furthermore, with the fourth region 104, the defect such as the crack portion 106 contained in the positive electrode active material 100 can be repaired.

[0195] The presence of the fourth region 104 and the shape of the fourth region 104 can be observed using a scanning electron microscope (SEM) or the like. Elements contained in the fourth region 104 can be analyzed using SEM-EDX or the like. [Method for forming a positive electrode active material]

[0196] Next, an example of a method for forming the positive electrode active material 100, which is an embodiment of the present invention, will be described. <Schritt 11: Herstellung der Ausgangsmaterialien>

[0197] First, starting materials are produced. The first region 101 and the third region 103 are then formed from the starting materials produced in this process.

[0198] A lithium source and a first transition metal source are prepared as materials for lithium and the first transition metal contained in the first region 101. In addition, a representative element source is prepared for the representative element compound materials contained in the third region 103.

[0199] In addition to these sources, a fluorine source is preferably prepared. Fluorine used for the materials has the effect of segregating the representative elements contained in the third region 103 onto the surface of the positive electrode active material 100 in a later step.

[0200] For example, lithium carbonate and lithium fluoride can be used as the lithium source. For example, an oxide of the first transition metal can be used as the source of the first transition metal. For example, an oxide of the representative element contained in the third region and a fluoride of the representative element contained in the third region can be used as the source of the representative element.

[0201] For example, lithium fluoride and a fluoride of the representative element contained in the third region can be used as the fluorine source. That is, lithium fluoride can be used either as the lithium source or as the fluorine source.

[0202] The amount of fluorine contained in the fluorine source is preferably 1.0 times to 4 times (atomic ratio), more preferably 1.5 times to 3 times (atomic ratio) the amount of the representative element contained in the source of the representative element. <Schritt 12: Mischen der Ausgangsmaterialien>

[0203] Next, the lithium source, the source of the first transition metal, and the source of the representative element are mixed. Additionally, the fluorine source is preferably added. For example, a ball mill and a bead mill can be used for mixing. <Schritt 13: Erstes Erwärmen>

[0204] Next, the materials mixed in step 12 are heated. In this step, the heating is sometimes referred to as baking or first heating. The heating is preferably performed at 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower. The heating time is preferably 2 hours or longer and 20 hours or shorter. The baking is preferably performed in a dry atmosphere such as dry air. In the dry atmosphere, for example, the dew point is preferably -50°C or lower, more preferably -100°C or lower. In this embodiment, heating is performed at 1000°C for 10 hours, the temperature rise rate is 200°C / h, and dry air, whose dew point is -109°C, flows at 10 l / min.The heated materials are then cooled to room temperature.

[0205] Through heating in step 13, the composite oxide of lithium and the first transition metal with a layered rock-salt crystal structure can be synthesized. At this time, the representative element and fluorine contained in the starting materials form a solid solution in the composite oxide. However, in some cases, some representative elements have already segregated on the surface of the composite oxide.

[0206] Additionally, pre-synthesized composite oxide particles containing lithium, cobalt, fluorine, and magnesium can be used as starting materials. In this case, steps 12 and 13 can be omitted. For example, lithium cobalt oxide particles (C-20F, manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.) can be used as one of the starting materials. The lithium cobalt oxide particle has a diameter of approximately 20 μm and contains fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus in a range that can be analyzed by XPS from the surface. <Schritt 14: Beschichten mit dem zweiten Übergangsmetall>

[0207] Next, the composite oxide of lithium and the first transition metal is cooled to room temperature. Then, the surface of the composite oxide particle of lithium and the first transition metal is coated with a material containing the second transition metal. In the formation process example, a sol-gel process is used.

[0208] First, the alkoxide of the second transition metal dissolved in alcohol and the composite oxide particles of lithium and the first transition metal are mixed.

[0209] For example, in the case where titanium is used as the second transition metal, TTIP can be used as the alkoxide of the second transition metal. Isopropanol, for example, can be used as the alcohol.

[0210] Next, the above mixed solution is stirred in an atmosphere containing water vapor. Stirring can be performed, for example, with a magnetic stirrer. The stirring time is not limited as long as the water and TTIP induce a hydrolysis and polycondensation reaction in an atmosphere. For example, stirring can be performed for 4 hours at 25°C and a humidity of 90%RH (relative humidity).

[0211] As described above, when water and TTIP react with each other in an atmosphere, a sol-gel reaction can proceed more slowly than when liquid water is added. Alternatively, when titanium alkoxide and water react with each other at room temperature, for example, a sol-gel reaction can proceed more slowly than when heating is carried out at a temperature above the boiling point of the alcohol, which is a solvent. A sol-gel reaction proceeds slowly, allowing a high-quality coating layer containing titanium with a uniform thickness to be formed.

[0212] After the above process, the precipitate is collected from the mixed solution. Filtration, centrifugation, evaporation, and drying, or the like, can be used as collection methods. In this embodiment, filtration is used. A paper filter is used for filtration, and the residue is washed with an alcohol similar to the solvent in which titanium alkoxide was dissolved.

[0213] The collected residue is then dried. In this embodiment, vacuum drying is carried out at 70 °C for one hour. <Schritt 15: Zweites Erwärmen>

[0214] Next, the composite oxide particle formed in step 14, which is coated with the material containing the second transition metal, is heated. This step is sometimes referred to as second heating. During heating, the residence time in a specified temperature range is preferably less than or equal to 50 hours, more preferably greater than or equal to 2 hours and less than or equal to 10 hours, and even more preferably greater than or equal to 1 hour and less than or equal to 3 hours. If the heating time is too short, there is a risk that the segregation of the representative elements will not occur. However, if the heating time is too long, there is a risk that the advantageous second region 102 will not be formed because the diffusion of the second transition metal progresses too much.

[0215] The specified temperature is preferably higher than or equal to 500°C and lower than or equal to 1200°C, more preferably higher than or equal to 800°C and lower than or equal to 1000°C. If the specified temperature is too low, there is a risk that the segregation of the representative elements and the second transition metal will not occur. However, if the specified temperature is too high, there is a risk that the first transition metal in the composite oxide particle will be reduced, thereby decomposing the composite oxide particle, that a layered structure of lithium and the first transition metal cannot be maintained in the composite oxide particle, and the like.

[0216] In this embodiment, the specified temperature is 800 °C and maintained for 2 hours, the temperature rise rate is 200 °C / h, and the flow rate (flow velocity) of dry air is 10 l / min.

[0217] Through the heating in step 15, the composite oxide of lithium and the first transition metal and the oxide of the second transition metal covering the composite oxide become a topotaxic layer. In other words, the first region 101 and the second region 102 become a topotaxic layer.

[0218] Through the heating in step 15, the representative elements forming a solid solution within the composite oxide particle of lithium and the first transition metal are unevenly distributed on the surface to form a solid solution; that is, the representative elements are segregated, the compound of representative elements is formed, and the third region 103 is formed. At this time, the compound of representative elements is formed by heteroepitaxial growth from the second region 102. That is, the second region 102 and the third region 103 become a topotaxy.

[0219] Since the second region 102 and the third region 103 contain crystals whose orientations are substantially aligned with each other and have a stable bond with the first region 101, a change in the crystal structure in the first region 101 caused by charging and discharging can be effectively suppressed when the positive electrode active material 100 is used for the secondary battery. Even if lithium is released from the first region 101 due to charging, the surface portion having a stable bond can suppress the release of oxygen and the first transition metal, such as cobalt, from the first region 101. Furthermore, a chemically stable material can be used for a region in contact with the electrolyte solution. Thus, a secondary battery with excellent cycle characteristics can be provided.

[0220] It should be noted that the entire first region 101 and the entire second region 102 do not need to become a topotaxy as long as a part of the first region 101 and a part of the second region 102 become a topotaxy. Furthermore, the entire second region 102 and the entire third region 103 do not need to become a topotaxy as long as a part of the second region 102 and a part of the third region 103 become a topotaxy.

[0221] If the combination of representative elements contained in the third region contains oxygen, the heating in step 15 is preferably carried out in an oxygen-containing atmosphere. Heating in an oxygen-containing atmosphere promotes the formation of the third region 103.

[0222] Furthermore, fluorine contained in the starting materials promotes the segregation of the representative elements.

[0223] In this way, in the method for forming the positive electrode active material of one embodiment of the present invention, after the elements constituting the second region 102 are coated, heating is performed to form the third region 103, and two types of regions can be formed on the surface of the positive electrode active material 100. That is, generally, two coating steps are required to provide two types of regions in one surface portion, but in the method for forming the positive electrode active material of one embodiment of the present invention, only one coating step (sol-gel process) is required, which is a high-productivity formation method. <Schritt 16: Kühlen>

[0224] Next, the particles heated in step 15 are cooled to room temperature. The temperature reduction time is preferably long because topotaxy is easily generated. For example, the temperature reduction time from the retention temperature to room temperature is preferably equal to or longer than the temperature increase time, particularly longer than or equal to 10 hours and shorter than or equal to 50 hours. <Schritt 17: Sammeln>

[0225] Next, the cooled particles are collected. Furthermore, the particles are preferably passed through a sieve. Through the above process, the positive electrode active material 100, which includes the first region 101, the second region 102, and the third region 103, can be formed.

[0226] This embodiment may be implemented in suitable combination with any of the other embodiments. (Embodiment 2)

[0227] In this embodiment, examples of materials that can be used for a secondary battery containing the positive electrode active material 100 described in the above embodiment are described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolyte solution are wrapped in an outer part is described as an example. [Positive electrode]

[0228] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. <positivelektrodenaktivmaterialschicht>

[0229] The positive electrode active material layer contains at least one positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer may contain other materials, such as a coating film of the active material surface, a conductive additive, and a binder.

[0230] As the positive electrode active material, the positive electrode active material 100 described in the above embodiment can be used. When the above-described positive electrode active material 100 is used, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0231] Examples of the conductive additive include a carbon material, a metal material, and a conductive ceramic material. Alternatively, a fiber material can be used as the conductive additive. The proportion of the conductive additive is preferably greater than or equal to 1 wt% and less than or equal to 10 wt%, more preferably greater than or equal to 1 wt% and less than or equal to 5 wt%, relative to the total amount of the active material layer.

[0232] An electrical conduction network can be formed by the conductive additive in the active material layer. The conductive additive also allows an electrical conduction path to be maintained between the positive electrode active material particles. The electrical conductivity of the active material layer is increased by adding the conductive additive to the active material layer.

[0233] Examples of the conductive additive include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fiber. Examples of a carbon fiber include a mesophase pitch-based carbon fiber, an isotropic pitch-based carbon fiber, a carbon nanofiber, and a carbon nanotube. A carbon nanotube can be formed, for example, by a vapor deposition method. Other examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite (tearing lead) particles, graphene, and fullerene. Alternatively, a metal powder or metal fiber of copper, nickel, aluminum, silver, gold, or the like, a conductive ceramic material, or the like can also be used.

[0234] Alternatively, a graphene compound can be used as a conductive additive.

[0235] A graphene compound exhibits excellent electrical properties, i.e., high conductivity, as well as excellent physical properties, i.e., high flexibility and high mechanical strength. Furthermore, a graphene compound exhibits a planar shape. A graphene compound enables low-resistance surface contact. Furthermore, in some cases, a graphene compound exhibits extremely high conductivity even at a small thickness, thus enabling the efficient formation of a conductive path in an active material layer, even in a small amount. For this reason, it is preferable to use a graphene compound as a conductive additive because the area in which the active material and the conductive additive are in contact with each other can be increased.The graphene compound serving as a conductive additive is preferably formed as a coating film to cover the entire surface of the active material using a spray-drying device, in which case the electrical resistance can be reduced. For example, graphene, multilayer graphene, or RGO are particularly preferably used as the graphene compound. Note that RGO refers to a compound obtained, for example, by reducing graphene oxide (GO).

[0236] When an active material with a small particle diameter (e.g., 1 μm or smaller) is used, the specific area of ​​the active material is large, and therefore, more conductive paths are required for the active material particles. Thus, the amount of conductive additive tends to increase, and the supported amount of active material tends to decrease in proportion. As the supported amount of active material decreases, the capacity of the secondary battery also decreases. In such a case, a graphene compound that can efficiently form a conductive path even in a small amount is particularly preferably used as the conductive additive because it prevents the supported amount of active material from decreasing.

[0237] An example of the cross-sectional structure of an active material layer 200 containing a graphene compound as a conductive additive will be described below.

[0238] Fig. 7A shows a longitudinal cross-sectional view of the active material layer 200. The active material layer 200 includes positive electrode active material particles 100, a graphene compound 201 serving as a conductive additive, and a binder (not shown). Graphene or multilayer graphene, for example, can be used as the graphene compound 201. The graphene compound 201 preferably has a sheet-like shape. The graphene compound 201 may have a sheet-like shape formed from multiple layers of multilayer graphene and / or multiple layers of graphene that partially overlap.

[0239] The cross section in the longitudinal direction of the active material layer 200 in Fig. Figure 7B shows a substantially uniform dispersion of the sheet-like graphene compounds 201 in the active material layer 200. The graphene compounds 201 are schematically indicated by thick lines in Fig. 7B, however, they are actually thin films, each having a thickness corresponding to the thickness of one or more layers of carbon molecules. The plurality of graphene compounds 201 are formed to partially cover or adhere to the surfaces of the plurality of positive electrode active material particles 100, so that the graphene compounds 201 come into surface contact with the positive electrode active material particles 100.

[0240] Here, the plurality of graphene compounds are interconnected to form a mesh-like graphene interconnect layer (hereinafter referred to as graphene interconnect network or graphene network). The graphene network covering the active material can serve as a binder for binding the active materials. Therefore, the amount of a binder can be reduced, or the binder need not be used. This can increase the proportion of the active material in terms of electrode volume or weight. This means that the capacity of the secondary battery can be increased.

[0241] Here, it is preferable to perform the reduction after a layer that will become the active material layer 200 has been formed by using graphene oxide as the graphene compound 201 and mixing it with an active material. When graphene oxide with extremely high dispersibility in a polar solvent is used to form the graphene compounds 201, the graphene compounds 201 can be substantially uniformly dispersed in the active material layer 200. The solvent is removed by volatilization from a dispersant in which graphene oxide is uniformly dispersed, and the graphene oxide is reduced; thus, the graphene compounds 201 remaining in the active material layer 200 partially overlap each other and are dispersed in such a way that surface contact is established, thereby forming a three-dimensional conductive path.It should be noted that graphene oxide can be reduced, for example, either by heat treatment or by using a reducing agent.

[0242] Unlike a particulate conductive additive, such as acetylene black, which comes into point contact with an active material, the graphene compound 201 can form a low-resistance surface contact. Consequently, the electrical connection between the positive electrode active material particles 100 and the graphene compounds 201 can be improved with a smaller amount of graphene compound 201 than with a conventional conductive additive. This increases the proportion of the positive electrode active material particles 100 in the active material layer 200, resulting in increased discharge capacity of the secondary battery.

[0243] Alternatively, the graphene compound can be pre-coated over the entire surface of the active material using a spray-drying device. Then, at the time of forming the positive electrode active material layer, a graphene compound can be further added to make the conduction path between the active materials more favorable.

[0244] A rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer can be used as a binder. Alternatively, fluororubber can be used as a binder.

[0245] For example, water-soluble polymers are preferably used for the binder. Polysaccharides and the like can be used as water-soluble polymers. A cellulose derivative such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, or regenerated cellulose, starch, or the like can be used as the polysaccharide. More preferably, such water-soluble polymers are used in combination with one of the above-mentioned rubber materials.

[0246] Alternatively, a material such as polystyrene, poly(methyl acrylate), poly(methyl methacrylate) (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylene-propylene-diene polymer, polyvinyl acetate or nitrocellulose is preferably used as the binder.

[0247] A variety of the above materials can be used in combination for the binder.

[0248] For example, a material having a significant viscosity-modifying effect and another material may be used in combination. For example, a rubber material or the like has high adhesion or high elasticity, but may have difficulty in mixing in a solvent for viscosity modification. In such a case, for example, a rubber material or the like is preferably blended with a material having a significant viscosity-modifying effect. As the material having a significant viscosity-modifying effect, a water-soluble polymer, for example, is preferably used. An example of a water-soluble polymer having a particularly significant viscosity-modifying effect is the above-mentioned polysaccharide; for example, a cellulose derivative such asCarboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose or regenerated cellulose, or starch may be used.

[0249] It should be noted that a cellulose derivative such as carboxymethylcellulose achieves higher solubility when converted into a salt, such as a sodium salt or an ammonium salt of carboxymethylcellulose, and thus readily exhibits an effect as a viscosity modifier. The high solubility can also increase the dispersibility of an active material and other components when forming a slurry for an electrode. In this specification, cellulose and a cellulose derivative used as a binder for an electrode include salts thereof.

[0250] The water-soluble polymers stabilize the viscosity by dissolving in water and enable stable dispersion of the active material and another material combined as a binder, such as styrene-butadiene rubber, in an aqueous solution. Furthermore, a water-soluble polymer is expected to be easily and stably adsorbed to a surface of the active material because it has a functional group. Many cellulose derivatives, such as carboxymethylcellulose, have functional groups such as a hydroxyl group and a carboxyl group. Due to functional groups, polymers are expected to interact with each other and cover a large area of ​​the active material's surface.

[0251] In the case where the binder covering the surface of the active material or in contact with the surface of the active material forms a film, the film is expected to serve as a passivation film to suppress the decomposition of the electrolyte solution. Here, the passivation film refers to a film with no electrical conductivity or a film with a very low electrical conductivity, and the passivation film can prevent the decomposition of an electrolyte solution at a potential at which a battery reaction occurs, for example, in the case where the passivation film is formed on the surface of the active material. Preferably, the passivation film can conduct lithium ions while suppressing electrical conductivity. <positivelektrodenstromkollektor>

[0252] The positive electrode current collector can be formed using a material having high conductivity, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that a material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Alternatively, the positive electrode current collector can be formed using an aluminum alloy to which a heat-resistance-enhancing element, such as silicon, titanium, neodymium, scandium, or molybdenum, has been added. As a further alternative, a metal element that forms silicide by reacting with silicon can be used. Examples of the metal element that forms silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.The current collector can have any of various shapes, including a foil-like shape, a plate-like shape (sheet-like shape), a mesh-like shape, a stamped metal shape, and an expanded metal shape. The current collector preferably has a thickness of 5 µm to 30 µm. [Negative electrode]

[0253] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may contain a conductive additive and a binder. <negativelektrodenaktivmaterial>

[0254] For example, an alloy-based material or a carbon-based material can be used as the negative electrode active material.

[0255] For the negative electrode active material, an element that enables charge / discharge reactions through an alloying reaction and a 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, and the like can be used. Such elements have a higher capacity than carbon. In particular, silicon has a very high theoretical capacity of 4200 mAh / g. Therefore, silicon is preferably used as the negative electrode active material. Alternatively, a compound containing any of the above elements can be used. Examples of the compound include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb and SbSn.Here, an element that enables charge / discharge reactions by an alloying reaction and a dealloying reaction with lithium, a compound containing the element, and the like can be referred to as an alloy-based material.

[0256] In this specification and the like, SiO refers to silicon monoxide, for example. SiO may alternatively be replaced by SiO x Here, x preferably has an approximate value of 1. For example, x is preferably 0.2 or greater and 1.5 or less, more preferably 0.3 or greater and 1.2 or less.

[0257] As a carbon-based material, graphite, graphitizing carbon (soft carbon), non-graphitizing carbon (hard carbon), carbon nanotube, graphene, carbon black, and the like can be used.

[0258] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite with a spherical shape can be used as artificial graphite. For example, MCMB is preferably used because it can have a spherical shape. Furthermore, MCMB is preferably used because it can be relatively light and has a small surface area. Examples of natural graphite include flake graphite and spherical natural graphite.

[0259] Graphite has a low potential, essentially equal to that of a lithium metal (greater than or equal to 0.05 V and lower than or equal to 0.3 V vs. Li / Li + ) occurs when lithium ions are intercalated into the graphite (while forming a lithium-graphite intercalation compound). For this reason, a lithium-ion secondary battery can have a high operating voltage. In addition, graphite is preferred for its advantages, such as its relatively high capacity per unit volume, its relatively small volume expansion, its low cost, and its higher level of safety than that of lithium metal.

[0260] Alternatively, an oxide such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2) or molybdenum oxide (MoO2).

[0261] As a further alternative, Li can be used as the negative electrode active material. 3-x M x N (M = Co, Ni or Cu) with a Li3N structure, which is a nitride containing lithium and a transition metal, can be used. For example, Li 2,6 Co 0,4 N3 due to its high charge and discharge capacity (900 mAh / g and 1890 mAh / cm 3 ) preferred.

[0262] A nitride containing lithium and a transition metal is preferably used. In this case, lithium ions are contained in the negative electrode active material, and therefore, the negative electrode active material can be used in combination with a material for a positive electrode active material that does not contain lithium ions, such as V2O5 or Cr3O8. In the case where a material containing lithium ions is used as the positive electrode active material, the nitride containing lithium and a transition metal can be used as the negative electrode active material by pre-exposing the lithium ions contained in the positive electrode active material.

[0263] Alternatively, a material that causes a conversion reaction can be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used. Other examples of the material that causes a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and sulfides such as CoS. 0,89 , NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0264] For the conductive additive and the binder that may be contained in the negative electrode active material layer, materials similar to those of the conductive additive and the binder that may be contained in the positive electrode active material layer may be used. <negativelektrodenstromkollektor>

[0265] A material similar to that of the positive electrode current collector can be used for the negative electrode current collector. Note that a material that is not alloyed with a carrier ion such as lithium is preferably used for the negative electrode current collector. [Electrolyte solution]

[0266] The electrolytic solution contains a solvent and an electrolyte. An aprotic organic solvent is preferably used as the solvent of the electrolytic solution. For example, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone can be used, or two or more of these solvents can be used in an appropriate combination in an appropriate ratio.

[0267] Alternatively, using one or more types of ionic liquids (molten salts at room temperature) as the solvent of the electrolyte solution, which have properties of non-flammability and non-volatility, can prevent a secondary battery from exploding or catching fire, even if the secondary battery is short-circuited internally or the internal temperature rises due to overcharging or the like. An ionic liquid contains a cation and an anion. The ionic liquid contains an organic cation and an anion. Examples of the organic cation used for the electrolyte solution include aliphatic onium cations, such as a quaternary ammonium cation, a tertiary sulfonium cation, and a quaternary phosphonium cation, and aromatic cations, such as an imidazolium cation and a pyridinium cation.Examples of the anion used for the electrolytic solution include a monovalent amide-based anion, a monovalent methide-based anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion, and a perfluoroalkylphosphate anion.

[0268] As an electrolyte dissolved in the solvent described above, a lithium salt such as LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiIl, Li2SO4, Li2B 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2) (CF3SO2) and LiN(C2F5SO2)2 may be used, or two or more of these lithium salts may be used in appropriate combination in an appropriate ratio.

[0269] The electrolyte solution used for a secondary battery is preferably highly purified and contains only a small amount of dust particles and other elements as constituent elements of the electrolyte solution (hereinafter also referred to simply as impurities). Specifically, the weight ratio of the impurities to the electrolyte solution is less than or equal to 1%, preferably less than or equal to 0.1%, and more preferably less than or equal to 0.01%.

[0270] Furthermore, an additive agent such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), LiBOB, or a dinitrile compound such as succinonitrile or adiponitrile can be added to the electrolyte solution. The concentration of a material to be added is, for example, greater than or equal to 0.1 wt% and less than or equal to 5 wt% with respect to the total solvent.

[0271] Alternatively, a gelled electrolyte obtained by swelling a polymer in an electrolyte solution can be used.

[0272] Using a polymer gel electrolyte improves safety against liquid leakage and the like. Furthermore, a secondary battery can be thinner and lighter.

[0273] As the polymer subjected to gelation, a silicone gel, an acrylic gel, an acrylonitrile gel, a polyethylene oxide-based gel, a polypropylene oxide-based gel, a fluorine-based polymer gel, or the like can be used.

[0274] Examples of the polymer include a polymer with a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and a copolymer containing any of them. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The resulting polymer can be porous.

[0275] Instead of the electrolyte solution, a solid electrolyte containing an inorganic material, such as a sulfide-based inorganic material or an oxide-based inorganic material, or a solid electrolyte containing a high-molecular-weight material, such as a high-molecular-weight material based on polyethylene oxide (PEO), can be used as an alternative. When using the solid electrolyte, a separator and spacer are unnecessary. Furthermore, since the battery can be fully solidified, there is no possibility of liquid leakage, dramatically increasing the safety of the battery. [Separator]

[0276] The secondary battery preferably includes a separator. Paper, nonwoven fabric, glass fibers, ceramics, or synthetic fibers containing nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyester, acrylic, polyolefin, or polyurethane can be used as the separator. The separator is preferably designed to have the shape of a pocket to enclose either the positive electrode or the negative electrode.

[0277] The separator may have a multilayer structure. For example, an organic material film, such as polypropylene or polyethylene, may be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, a mixture thereof, or the like. Examples of the ceramic-based material include alumina particles and silica particles. Examples of the fluorine-based material include PVDF and polytetrafluoroethylene. Examples of the polyamide-based material include nylon and aramid (meta-based aramid and para-based aramid).

[0278] Separator deterioration during high-voltage charging and discharging can be suppressed, and thus, secondary battery reliability can be improved because oxidation resistance is improved when the separator is coated with a ceramic-based material. Furthermore, when the separator is coated with a fluorine-based material, the separator easily comes into close contact with an electrode, resulting in high output characteristics. When the separator is coated with a polyamide-based material, especially aramid, the safety of the secondary battery is improved because heat resistance is improved.

[0279] For example, both surfaces of a polypropylene film can be coated with a mixed material of aluminum oxide and aramid. Alternatively, a surface of the polypropylene film in contact with the positive electrode can be coated with the mixed material of aluminum oxide and aramid, and a surface of the polypropylene film in contact with the negative electrode can be coated with the fluorine-based material.

[0280] By using a separator with a multi-layer structure, the capacity of the secondary battery per volume can be increased because the safety of the secondary battery can be maintained even if the total thickness of the separator is small. [Outer part]

[0281] For an outer part included in the secondary battery, for example, a metal material such as aluminum and a resin material can be used. An outer part in the form of a film can also be used. As the film, for example, a film having a three-layer structure in which a highly flexible thin metal film made of aluminum, stainless steel, copper, nickel, or the like is arranged over a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film made of a polyamide-based resin, a polyester-based resin, or the like is arranged over the thin metal film as the outer surface of the outer part, can be used. [Loading and discharging procedures]

[0282] For example, the secondary battery can be charged and discharged in the following way. < <cc-ladung>>

[0283] First, CC charging, which is one of the charging methods, will be described. CC charging is a charging method in which a constant current flows to a secondary battery throughout the charging period, and charging is terminated when the voltage reaches a predetermined voltage. The secondary battery is assumed to be an equivalent circuit with an internal resistance R and a secondary battery capacitance or capacitor C, as shown in Fig. 8A. In this case, a secondary battery voltage V B the sum of a voltage V applied to the internal resistance R R and a voltage V applied to the secondary battery capacity C C .

[0284] While the CC charge is being performed, a switch is turned on, as shown in Fig. 8A, so that a constant current I flows to the secondary battery. During the period, the current I is constant; according to Ohm's law (V R = R × I) is the voltage V applied to the internal resistance R R is therefore also constant. In contrast, the voltage V applied to the secondary battery capacity C increases C over time. Accordingly, the secondary battery voltage V B over time.

[0285] When the secondary battery voltage V B a predetermined voltage is reached, e.g., 4.3 V, the charge is stopped. When the CC charge is finished, the switch is turned off, as shown in Fig. 8B, and the current I becomes 0. Thus, the voltage V applied to the internal resistance R R 0 V. Consequently, the secondary battery voltage V B reduced by the lost voltage drop in the internal resistance R.

[0286] Fig. Figure 8C shows an example of the secondary battery voltage V B and the charging current during a period in which the CC charge is being performed and after the CC charge is completed. The secondary battery voltage V B increases while the CC charge is being performed and decreases slightly after the CC charge is completed. < <cccv-ladung>>

[0287] Next, CCCV charging, which is a charging method different from the method described above, will be described. CCCV charging is a charging method in which CC charging is performed until the voltage reaches a predetermined voltage, and then constant voltage charging (CV charging) is performed until the current flow rate becomes small, specifically, a terminal current value.

[0288] While the CC charge is being performed, a switch of a constant current source is turned on and a switch of a constant voltage source is turned off, as shown in Fig. 9A, so that the constant current I flows to the secondary battery. During the period, the current I is constant; according to Ohm's law (V R = R × I) is the voltage V applied to the internal resistance R R is therefore also constant. In contrast, the voltage V applied to the secondary battery capacity C increases C over time. Accordingly, the secondary battery voltage V B over time.

[0289] When the secondary battery voltage V B When a predetermined voltage is reached, e.g., 4.3 V, the switch from CC charging to CV charging is performed. While CV charging is performed, the switch of the constant voltage source is turned on and the switch of the constant current source is turned off, as shown in Fig. 9B; thus, the secondary battery voltage V B constant. In contrast, the voltage V applied to the secondary battery capacity C increases C over time. Since V B = V R + V C is fulfilled, the voltage V applied to the internal resistance R R decreases over time. If the voltage V applied to the internal resistance R R decreases, the current I flowing to the secondary battery also decreases according to Ohm's law (V R = R × I).

[0290] When the current I flowing to the secondary battery reaches a predetermined current, e.g., approximately 0.01 C, charging is stopped. When the CCCV charge is stopped, all switches are turned off, as shown in Fig. 9C, so that the current I becomes 0. Thus, the voltage V applied to the internal resistance R R to 0 V. However, the voltage V applied to the internal resistance R R sufficiently small due to the CV charge; even if there is no longer a voltage drop in the internal resistance R, the secondary battery voltage V B hardly any.

[0291] Fig. 9D shows an example of the secondary battery voltage V B and the charging current during a period in which the CCCV charge is being performed and after the completion of the CCCV charge. Even after the CCCV charge has been completed, the secondary battery voltage V B hardly any. < <cc-entladung>>

[0292] Next, a CC discharge, which is one of the discharge methods, will be described. CC discharge is a discharge method in which a constant current flows from the secondary battery throughout the discharge period, and the discharge is terminated when the secondary battery voltage V B a predetermined voltage, e.g., 2.5 V, is reached.

[0293] Fig. 10 shows an example of the secondary battery voltage V B and the discharge current while the CC discharge is being performed. As the discharge progresses, the secondary battery voltage V B away.

[0294] Next, a discharge rate and a charge rate are described. The discharge rate refers to the relative ratio of the discharge current to the battery capacity and is expressed in a unit C. A current of approximately 1 C in a battery with a nominal capacity X (Ah) is X A. The case where discharging is performed at a current of 2XA is reformulated as follows: Discharge is performed at 2 C. The case where discharging is performed at a current of X / 5 A is reformulated as follows: Discharge is performed at 0.2 C. The case where charging is performed at a current of 2X A is similarly reformulated as follows: Charging is performed at 2 C, and the case where charging is performed at a current of X / 5 A is reformulated as follows: Charging is performed at 0.2 C. (Embodiment 3)

[0295] In this embodiment, examples of a form of a secondary battery containing the positive electrode active material 100 described in the above embodiment will be described. For the materials used for the secondary battery described in this embodiment, reference can be made to the description of the above embodiment. [Button cell secondary battery]

[0296] First, an example of a button cell secondary battery is described. Fig. 11A is an external view of a button cell (single-layer flat) secondary battery, and Fig. 11B is a cross-sectional view thereof.

[0297] In a button cell secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed from each other by a gasket 303 made of polypropylene or the like. A positive electrode 304 includes a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector 305. A negative electrode 307 includes a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector 308.

[0298] It should be noted that only one surface of each of the positive electrode 304 and the negative electrode 307 used for the button cell secondary battery 300 is provided with an active material layer.

[0299] For the positive electrode can 301 and the negative electrode can 302, a metal with corrosion resistance to an electrolyte solution, such as nickel, aluminum, or titanium, an alloy of such a metal, or an alloy of such a metal and another metal (e.g., stainless steel) can be used. Alternatively, the positive electrode can 301 and the negative electrode can 302 are preferably coated with nickel, aluminum, or the like to prevent corrosion due to the electrolyte solution. The positive electrode can 301 and the negative electrode can 302 are electrically connected to the positive electrode 304 and the negative electrode 307, respectively.

[0300] The negative electrode 307, the positive electrode 304 and the separator 310 are immersed in the electrolyte solution. As in Fig. Then, as shown in Figure 11B, the positive electrode 304, the separator 310, the negative electrode 307, and the negative electrode can 302 are stacked in this order, with the positive electrode can 301 at the bottom, and the positive electrode can 301 and the negative electrode can 302 are pressure-bonded with the gasket 303 therebetween. In this way, the button cell secondary battery 300 can be manufactured.

[0301] When the positive electrode active material described in the above embodiment is used in the positive electrode 304, the button cell secondary battery 300 with high capacity and excellent cycle characteristics can be obtained.

[0302] Here, a current flow when charging a secondary battery is described with reference to Fig. 11C. If a secondary battery using lithium is considered a closed circuit, lithium ions move in the same direction as the current flows. Note that in the secondary battery using lithium, an anode and a cathode exchange roles during charging and discharging, and an oxidation reaction and a reduction reaction take place on the corresponding sides; therefore, an electrode with a high reaction potential is called a positive electrode, and an electrode with a low reaction potential is called a negative electrode. For this reason, in this specification, the positive electrode is referred to as the "positive electrode" or "plus electrode" and the negative electrode as the "negative electrode" or "minus electrode" in all cases where charging is performed, discharging is performed, a reverse pulse current is supplied, and a charging current is supplied.The use of the terms "anode" and "cathode," which refer to an oxidation reaction and a reduction reaction, could lead to confusion, as the anode and cathode exchange their roles during charging and discharging. Therefore, the terms "anode" and "cathode" are not used in this description. Whenever the term "anode" or "cathode" is used, it should always be mentioned whether the anode or the cathode is being used during charging or discharging, respectively, and which electrode they correspond to, a positive (plus) electrode or a negative (minus) electrode.

[0303] Two connections in Fig. 11C are connected to a charger, and the button cell secondary battery 300 is being charged. As the charging of the button cell secondary battery 300 progresses, the potential difference between the electrodes becomes greater. [Cylindrical secondary battery]

[0304] Next, an example of a cylindrical secondary battery will be described with reference to Fig. 12A to Fig. 12D. A cylindrical secondary battery 600 includes, as shown in Fig. 12A, a positive electrode cap (battery cover) 601 is provided on the top surface and a battery can (outer can) 602 is provided on the side surface and the bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated from each other by a gasket (insulating gasket) 610.

[0305] Fig. 12B is a schematic cross-sectional view of the cylindrical secondary battery. Within the battery can 602, which has a hollow cylindrical shape, there is provided a battery element in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with a strip-shaped separator 605 therebetween. Although not shown, the battery element is wound around a central pin. One end of the battery can 602 is closed, and the other end is open. For the battery can 602, a metal having corrosion resistance to an electrolyte solution, such as nickel, aluminum, or titanium, an alloy of such a metal, or an alloy of such a metal and another metal (e.g., stainless steel) can be used.Alternatively, the battery can 602 is preferably coated with nickel, aluminum, or the like to prevent corrosion due to the electrolytic solution. Within 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 insulating plates 608 and 609 facing each other. Furthermore, a non-aqueous electrolytic solution (not shown) is injected into the battery can 602 provided with the battery element. As the non-aqueous electrolytic solution, a non-aqueous electrolytic solution similar to that of a button cell secondary battery can be used.

[0306] Since the positive electrode and the negative electrode of the cylindrical secondary battery are wound, active materials are preferably formed on both sides of the current collectors. A positive electrode terminal (positive electrode current collecting line) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collecting line) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be formed using a metal material such as aluminum. The positive electrode terminal 603 and the negative electrode terminal 607 are resistance-welded to a safety valve mechanism 612 and the bottom of the battery can 602, respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a positive temperature coefficient (PTC) element 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 exceeds a predetermined threshold. To prevent abnormal heat generation, the PTC element 611, which serves as a heat-sensitive resistor whose resistance increases with temperature rise, limits the amount of current by increasing its resistance. A barium titanate (BaTiO3)-based semiconductor ceramic can be used for the PTC element.

[0307] Alternatively, as in Fig. 12C, a plurality of cylindrical secondary batteries 600 may be arranged between a conductive plate 613 and a conductive plate 614 to form a module 615. The plurality of cylindrical secondary batteries 600 may be connected in parallel, in series, or in series after being connected in parallel. With the module 615 including the plurality of cylindrical secondary batteries 600, a large amount of electrical energy can be extracted.

[0308] Fig. Figure 12D is a top view of the module 615. The conductive plate 613 is shown by a dashed line for clarity. As shown in Fig. As shown in Figure 12D, the module 615 may include a line 616 that electrically connects the plurality of cylindrical secondary batteries 600. It is possible to provide the conductive plate 613 over the line 616 so that they overlap. Additionally, a temperature control device 617 may be provided between the plurality of cylindrical secondary batteries 600. When the cylindrical secondary batteries 600 become overheated, the temperature control device 617 may cool them, and when the cylindrical secondary batteries 600 become overcooled, the temperature control device 617 may heat them. Thus, the performance of the module 615 is not easily affected by the outside air temperature.

[0309] When the positive electrode active material described in the above embodiment is used in the positive electrode 604, the cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be obtained. [Structural examples of a secondary battery]

[0310] Further structural examples of secondary batteries are given with reference to Fig. 13A and Fig. 13B, Fig. 14A-1, Fig. 14A-2, Fig. 14B-1 and Fig. 14B-2, Fig. 15A and Fig. 15B and Fig. 16 described.

[0311] Fig. 13A and Fig. 13B are external views of a secondary battery. The secondary battery includes a circuit board 900 and a secondary battery 913. A label 910 is adhered to the secondary battery 913. As shown in Fig. 13B, the secondary battery further includes a terminal 951, a terminal 952, an antenna 914, and an antenna 915.

[0312] The circuit board 900 includes terminals 911 and a circuit 912. The terminals 911 are connected to the terminals 951 and 952, the antennas 914 and 915, and the circuit 912. Note that a plurality of terminals 911 serving as a control signal input terminal, a power supply terminal, and the like may be provided.

[0313] The circuit 912 may be arranged on the back of the circuit board 900. The shape of the antennas 914 and 915 is not limited to the shape of a coil and may be a linear shape or a plate shape. Furthermore, a planar antenna, an aperture antenna, a traveling-wave antenna, an EH antenna, a magnetic-field antenna, a dielectric antenna, or the like may be used. Alternatively, the antenna 914 or the antenna 915 may be a flat conductor. The flat conductor may serve as a conductor for electric field coupling. That is, the antenna 914 or the antenna 915 may serve as one of two conductors of a capacitor. Therefore, electrical energy can be transmitted and received not only by an electromagnetic field or a magnetic field, but also by an electric field.

[0314] The linewidth of antenna 914 is preferably larger than that of antenna 915. This may increase the amount of electrical energy received by antenna 914.

[0315] The secondary battery includes a layer 916 between the secondary battery 913 and the antennas 914 and 915. The layer 916 has, for example, a function of blocking an electromagnetic field from the secondary battery 913. For example, a magnetic body can be used as the layer 916.

[0316] It should be noted that the structure of the secondary battery is not limited to the Fig. 13A and Fig. 13B is limited.

[0317] For example, as in Fig. 14A-1 and Fig. 14A-2, two opposite surfaces of the secondary battery 913 in Fig. 13A and Fig. 13B be provided with respective antennas. Fig. 14A-1 is an external view showing one side of the opposing surfaces, and Fig. 14A-2 is an external view showing the other side of the opposing surfaces. For sections similar to those in Fig. 13A and Fig. 13B, may reasonably be referred to a description of the Fig. 13A and Fig. 13B shown secondary battery.

[0318] As in Fig. 14A-1, the antenna 914 is arranged on one of the opposite surfaces of the secondary battery 913 with the layer 916 therebetween, and as shown in Fig. As shown in Figure 14A-2, an antenna 918 is provided on the other of the opposite surfaces of the secondary battery 913, with the layer 917 interposed therebetween. The layer 917 has, for example, a function of blocking an electromagnetic field from the secondary battery 913. A magnetic body, for example, can be used as the layer 917.

[0319] With the above structure, both the antenna 914 and the antenna 918 can be enlarged. For example, the antenna 918 has a function for data communication with an external device. For example, an antenna having a shape that can be applied to the antenna 914 can be used as the antenna 918. As a system for communicating using the antenna 918 between the secondary battery and another device, a response method that can be used between the secondary battery and another device, such as NFC, can be used.

[0320] Alternatively, as in Fig. 14B-1, the secondary battery 913 in Fig. 13A and Fig. 13B may be provided with a display device 920. The display device 920 is electrically connected to the terminal 911. It is possible that the label 910 is not provided in a section in which the display device 920 is arranged. For sections similar to those in Fig. 13A and Fig. 13B, may reasonably be referred to a description of the Fig. 13A and Fig. 13B shown secondary battery.

[0321] For example, the display device 920 may display an image showing whether charging is currently being performed, an image showing the amount of stored energy, or the like. Electric paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like may be used as the display device 920. For example, the use of electric paper can reduce the power consumption of the display device 920.

[0322] Alternatively, as in Fig. 14B-2, the secondary battery 913 in Fig. 13A and Fig. 13B may be provided with a sensor 921. The sensor 921 is electrically connected to the terminal 911 via a terminal 922. For sections corresponding to those in Fig. 13A and Fig. 13B, may reasonably be referred to a description of the Fig. 13A and Fig. 13B shown secondary battery.

[0323] For example, sensor 921 has a function for measuring displacement, position, speed, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electrical energy, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. For example, sensor 921 can determine data about an environment (e.g., temperature) in which the secondary battery is located and store it in a memory within circuit 912.

[0324] Further, structural examples of the secondary battery 913 are described with reference to Fig. 15A and Fig. 15B and Fig. 16 described.

[0325] The Fig. The secondary battery 913 shown in Figure 15A includes a wound member 950 provided with terminals 951 and 952 in a casing 930. The wound member 950 is immersed in an electrolyte solution within the casing 930. The terminal 952 is in contact with the casing 930. An insulator or the like prevents contact between the terminal 951 and the casing 930. It should be noted that Fig. 15A illustrates the housing 930 divided into two pieces for simplicity; however, in the actual structure, the wound part 950 is covered with the housing 930, and the terminals 951 and 952 extend outside the housing 930. A metal material (e.g., aluminum) or a resin material can be used for the housing 930.

[0326] It should be noted that, as in Fig. 15B, the housing 930 in Fig. 15A can be formed using a variety of materials. In the secondary battery 913 in Fig. 15B, for example, a housing 930a and a housing 930b are fixed to each other, and the wound part 950 is arranged in a region enclosed by the housing 930a and the housing 930b.

[0327] An insulating material such as an organic resin can be used for the housing 930a. Specifically, if a material such as an organic resin is used for the side where an antenna is formed, an electric field from the secondary battery 913 can be prevented from being blocked. If an electric field is only slightly blocked by the housing 930a, an antenna such as the antenna 914 or the antenna 915 can be arranged inside the housing 930. For the housing 930b, for example, a metal material can be used.

[0328] Fig. 16 illustrates the structure of the wound part 950. The wound part 950 includes a negative electrode 931, a positive electrode 932, and separators 933. The wound part 950 is obtained by winding a sheet of foil in a stack in which the negative electrode 931 overlaps the positive electrode 932 with the separator 933 interposed therebetween. Note that a plurality of sheet foils, each including the negative electrode 931, the positive electrode 932, and the separator 933, may be stacked.

[0329] The negative electrode 931 is connected to the terminal 911 via one of the terminals 951 and 952 in Fig. 13A and Fig. 13B. The positive electrode 932 is connected to the terminal 911 via the other of the terminals 951 and 952 in Fig. 13A and Fig. 13B connected.

[0330] When the positive electrode active material described in the above embodiment is used in the positive electrode 932, the secondary battery 913 with high capacity and excellent cycle characteristics can be obtained. [laminated secondary battery]

[0331] Next, an example of a laminated secondary battery will be described with reference to Fig. 17A to Fig. 17C, Fig. 18A and Fig. 18B, Fig. 19, Fig. 20, Fig. 21A to Fig. 21C, Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D and Fig. 23A and Fig. 23B. When the laminated secondary battery has flexibility and is used in an electrical device in which at least one part is flexible, the secondary battery can be bent together with the electrical device.

[0332] A laminated secondary battery 980 is described with reference to Fig. 17A to Fig. 17C. The laminated secondary battery 980 comprises a Fig. 17A. The wound part 993 comprises a negative electrode 994, a positive electrode 995 and a separator 996. The wound part 993 is, in the same way as the one shown in Fig. 16, is obtained by winding a foil web of a stack in which the negative electrode 994 overlaps with the positive electrode 995, with the separator 996 therebetween.

[0333] Note that the number of foil sheets each comprising the negative electrode 994, the positive electrode 995, and the separator 996 is appropriately determined depending on the required capacity and volume of an element. The negative electrode 994 is connected to a negative electrode current collector (not shown) via a terminal electrode 997 or a terminal electrode 998. The positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the terminal electrode 997 and the terminal electrode 998.

[0334] As in Fig. 17B, ​​the wound part 993 is packed into a space formed by bonding a film 981 and a film 982 with a recessed part serving as an outer part by thermocompression bonding or the like, whereby, as shown in Fig. 17C, the laminated secondary battery 980 can be formed. The wound part 993 includes the terminal electrode 997 and the terminal electrode 998 and is immersed in an electrolytic solution within a space enclosed by the film 981 and the film 982 with a recessed part.

[0335] For the film 981 and the film 982 with a recessed portion, for example, a metal material such as aluminum or a resin material can be used. By using a resin material for the film 981 and the film 982 with a recessed portion, the shapes of the film 981 and the film 982 with a recessed portion can be changed when an external force is applied; thus, a flexible secondary battery can be manufactured.

[0336] Although Fig. 17B and Fig. 17C illustrates an example in which a space is formed by two films, the wound part 993 may be located in a space formed by bending a film.

[0337] When the positive electrode active material described in the above embodiment is used in the positive electrode 932, the laminated secondary battery 980 with high capacity and excellent cycle characteristics can be obtained.

[0338] In Fig. 17A to Fig. 17C, an example is described in which the laminated secondary battery 980 includes a wound part in a space formed by films serving as an outer part; as shown in Fig. 18A and Fig. However, as shown in Fig. 18B, a secondary battery may include a plurality of strip-shaped positive electrodes, a plurality of strip-shaped separators, and a plurality of strip-shaped negative electrodes in a space formed by films serving as an exterior part, for example.

[0339] A laminated secondary battery 500, which is Fig. 18A includes a positive electrode 503 including a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 including a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolytic solution 508, and an outer member 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 in the outer member 509. The outer member 509 is filled with the electrolytic solution 508. The electrolytic solution described in Embodiment 2 can be used for the electrolytic solution 508.

[0340] The laminated secondary battery 500, which is Fig. 18A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with an external portion. For this reason, the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged such that a part of the positive electrode current collector 501 and a part of the negative electrode current collector 504 are exposed to the outside of the outer part 509. Alternatively, a lead electrode may be ultrasonically welded to the positive electrode current collector 501 or the negative electrode current collector 504, so that the lead electrode is exposed to the outside of the outer part 509 instead of the positive electrode current collector 501 and the negative electrode current collector 504.

[0341] As the outer part 509 of the laminated secondary battery 500, for example, a laminated film having a three-layer structure in which a highly flexible thin metal film made of aluminum, stainless steel, copper, nickel, or the like is disposed over a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film made of a polyamide-based resin, a polyester-based resin, or the like is disposed over the thin metal film as the outer surface of the outer part can be used.

[0342] Fig. 18B shows an example of a cross-sectional structure of the laminated secondary battery 500. Although for the sake of simplicity, only two current collectors are shown in Fig. 18A, a real battery comprises a plurality of electrode layers.

[0343] The example in Fig. 18B includes 16 electrode layers. The laminated secondary battery 500 exhibits flexibility despite including the 16 electrode layers. Fig. Fig. 18B shows a structure comprising 8 layers of negative electrode current collectors 504 and 8 layers of positive electrode current collectors 501, ie, a total of 16 layers. It should be noted that Fig. 18B shows a cross section of the negative electrode terminal portion, and the eight negative electrode current collectors 504 are connected to each other by ultrasonic welding. Needless to say, the number of electrode layers is not limited to 16 and may be greater than or less than 16. With a large number of electrode layers, the secondary battery can have a high capacity. In contrast, with a small number of electrode layers, the secondary battery can have a small thickness and high flexibility.

[0344] Fig. 19 and Fig. 20 each show an example of the external view of the laminated secondary battery 500. In Fig. 19 and Fig. 20 includes the positive electrode 503, the negative electrode 506, the separator 507, the outer part 509, a positive electrode terminal electrode 510, and a negative electrode terminal electrode 511.

[0345] Fig. 21A shows external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 includes the positive electrode current collector 501, and the positive electrode active material layer 502 is formed on a surface of the positive electrode current collector 501. The positive electrode 503 also includes a region where a part of the positive electrode current collector 501 is exposed (hereinafter referred to as a tab region). The negative electrode 506 includes the negative electrode current collector 504, and the negative electrode active material layer 505 is formed on a surface of the negative electrode current collector 504. The negative electrode 506 also includes a region where a part of the negative electrode current collector 504 is exposed, that is, a tab region. The areas and shapes of the label areas in the positive electrode and the negative electrode are not limited to those in Fig. 21A. [Method for manufacturing the laminated secondary battery]

[0346] An example of a method for manufacturing the laminated secondary battery whose external view is shown in Fig. 19 is presented with reference to Fig. 21B and Fig. 21C described.

[0347] First, the negative electrode 506, the separator 507 and the positive electrode 503 are arranged one above the other. Fig. 21B illustrates the layered arrangement including the negative electrode 506, the separator 507, and the positive electrode 503. The secondary battery described here as an example includes five negative electrodes and four positive electrodes. The label portions of the positive electrodes 503 are then connected to each other, and the positive electrode terminal electrode 510 is attached to the label portion of the positive electrode located on the outermost surface. The bonding can be performed, for example, by ultrasonic welding. Similarly, the label portions of the negative electrodes 506 are connected to each other, and the negative electrode terminal electrode 511 is attached to the label portion of the negative electrode located on the outermost surface.

[0348] Thereafter, the negative electrode 506, the separator 507 and the positive electrode 503 are arranged over the outer part 509.

[0349] The outer part 509 is then folded along a dashed line, as in Fig. 21C. The outer edges of the outer part 509 are then joined together. The joining can be performed, for example, by thermocompression bonding. A portion (or side) of the outer part 509 remains unconnected (to provide an inlet) so that the electrolyte solution 508 can be introduced later.

[0350] Next, the electrolyte solution 508 is introduced into the outer part 509 through the inlet of the outer part 509. The electrolyte solution 508 is preferably introduced in a reduced-pressure atmosphere or in an inert gas atmosphere. Finally, the inlet is closed by bonding. In the above manner, the laminated secondary battery 500 can be manufactured.

[0351] When the positive electrode active material described in the above embodiment is used in the positive electrode 503, the laminated secondary battery 500 with high capacity and excellent cycle characteristics can be obtained. [Flexible secondary battery]

[0352] Next, an example of a flexible secondary battery will be described with reference to Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D and Fig. 23A and Fig. 23B.

[0353] Fig. 22A is a schematic plan view of a flexible secondary battery 50. Fig. 22B1, Fig. 22B2 and Fig. 22C are schematic cross-sectional views along section line C1-C2, section line C3-C4 and section line A1-A2, respectively, in Fig. 22A. The battery 50 includes an outer part 51 and a positive electrode 11a, as well as a negative electrode 11b held in the outer part 51. A lead 12a electrically connected to the positive electrode 11a and a lead 12b electrically connected to the negative electrode 11b extend to the outside of the outer part 51. In addition to the positive electrode 11a and the negative electrode 11b, an electrolyte solution (not shown) is enclosed in a region surrounded by the outer part 51.

[0354] Fig. 23A and Fig. 23B illustrates the positive electrode 11a and the negative electrode 11b included in the battery 50. Fig. 23A is a perspective view showing the arrangement order of the positive electrode 11a, the negative electrode 11b, and the separator 14. Fig. 23B is a perspective view showing the lead 12a and the lead 12b in addition to the positive electrode 11a and the negative electrode 11b.

[0355] As in Fig. As shown in Figure 23A, the battery 50 includes a plurality of strip-shaped positive electrodes 11a, a plurality of strip-shaped negative electrodes 11b, and a plurality of separators 14. The positive electrode 11a and the negative electrode 11b each include a protruding label portion and a portion other than the label. A positive electrode active material layer is formed on a surface of the positive electrode 11a other than the label portion, and a negative electrode active material layer is formed on a surface of the negative electrode 11b other than the label portion.

[0356] The positive electrodes 11a and the negative electrodes 11b are arranged one above the other such that the surfaces of the positive electrodes 11a on each of which the positive electrode active material layer is not formed are in contact with each other and that the surfaces of the negative electrodes 11b on each of which the negative electrode active material layer is not formed are in contact with each other.

[0357] Furthermore, the separator 14 is provided between the surface of the positive electrode 11a on which the positive electrode active material is formed and the surface of the negative electrode 11b on which the negative electrode active material is formed. Fig. 23A, the separator 14 is shown by a dashed line for ease of viewing.

[0358] As in Fig. 23B, the plurality of positive electrodes 11a are also electrically connected to the lead 12a in a connecting portion 15a. The plurality of negative electrodes 11b are electrically connected to the lead 12b in a connecting portion 15b.

[0359] Next, the outer part 51 is described with reference to Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D described.

[0360] The outer part 51 has a film-like shape and is folded in half with the positive electrodes 11a and the negative electrodes 11b between the facing portions of the outer part 51. The outer part 51 includes a bending portion 61, a pair of sealing portions 62, and a sealing portion 63. The pair of sealing portions 62 are provided with the positive electrodes 11a and the negative electrodes 11b positioned therebetween and can therefore also be referred to as side seals. The sealing portion 63 has portions that overlap with the lead 12a and the lead 12b and can also be referred to as the top seal.

[0361] A portion of the outer part 51 that overlaps the positive electrodes 11a and the negative electrodes 11b preferably has a wave shape in which ridge lines 71 and valley lines 72 are alternately arranged. The sealing portions 62 and the sealing portion 63 of the outer part 51 are preferably flat.

[0362] Fig. 22B1 shows a cross section along the part overlapping with the ridge line 71. Fig. 22B2 shows a cross section along the part overlapping with valley line 72. Fig. 22B1 and Fig. 22B2 correspond to cross sections of the battery 50, the positive electrodes 11a and the negative electrodes 11b in the width direction.

[0363] The distance between an end portion of the negative electrode 11b in the width direction and the sealing portion 62 is referred to as the distance La. When the shape of the battery 50 changes, for example, due to bending, the shape of the positive electrode 11a and the negative electrode 11b changes such that their positions in the longitudinal direction are shifted from each other, as described later. If the distance La is too short, the outer part 51 and the positive electrode 11a and the negative electrode 11b will rub against each other harshly at this time, so that the outer part 51 will be damaged in some cases. In particular, if a metal film of the outer part 51 is exposed, there is a risk that the metal film will be corroded by the electrolytic solution. Thus, the distance La is preferably set as long as possible. However, if the distance La is too long, the volume of the battery 50 will increase.

[0364] The distance La between the end portion of the negative electrode 11b and the sealing portion 62 is preferably increased as the total thickness of the stacked positive electrodes 11a and negative electrodes 11b is increased.

[0365] Specifically, when the total thickness of the stacked positive electrodes 11a and negative electrodes 11b and separators 14 is referred to as thickness t, the distance La is preferably 0.8 times or more and 3.0 times or less, more preferably 0.9 times or more and 2.5 times or less, even more preferably 1.0 times or more and 2.0 times or less of the thickness t. When the distance La is in the above-described range, a compact battery that is highly reliable in bending can be obtained.

[0366] Further, when a distance between the pair of sealing portions 62 is referred to as a distance Lb, the distance Lb is preferably sufficiently longer than a width Wb of the negative electrode 11b. In this case, even when the positive electrode 11a and the negative electrode 11b come into contact with the outer member 51 due to a change in the shape of the battery 50, such as repeated bending, the position of a part of the positive electrode 11a and the negative electrode 11b can be shifted in the width direction; thus, the positive and negative electrodes 11a and 11b and the outer member 51 can be effectively prevented from rubbing against each other.

[0367] For example, the difference between the distance Lb (ie, the distance between the pair of sealing portions 62) and the width Wb of the negative electrode 11b is preferably 1.6 times or more and 6.0 times or less, more preferably 1.8 times or more and 5.0 times or less, even more preferably 2.0 times or more and 4.0 times or less of the total thickness t of the positive electrode 11a and the negative electrode 11b.

[0368] In other words, the distance Lb, the width Wb and the thickness t preferably satisfy the relationship of the following formula 2. [Formula 2] Lb−Wb2t≥a

[0369] In the formula, a is 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, more preferably 1.0 or more and 2.0 or less.

[0370] Fig. 22C shows a cross section including the lead 12a and corresponds to a cross section of the battery 50, the positive electrode 11a, and the negative electrode 11b in the longitudinal direction. As shown in Fig. 22C, a space 73 is preferably provided between the end portions of the positive electrode 11a and the negative electrode 11b in the longitudinal direction and the outer part 51 in the bending portion 61.

[0371] Fig. 22D is a schematic cross-sectional view of the battery 50 in a bent state. Fig. 22D corresponds to a cross section along the section line B1-B2 in Fig. 22A.

[0372] When the battery 50 is bent, a part of the outer part 51 positioned on the outside during bending remains unbent, and another part positioned on the inside changes its shape as it shrinks. Specifically, the part of the outer part 51 positioned on the outside during bending changes its shape such that the wave amplitude becomes smaller and the length of the wave period becomes longer. In contrast, the part of the outer part 51 positioned on the inside during bending changes its shape such that the wave amplitude becomes larger and the length of the wave period becomes shorter. When the outer part 51 changes its shape in this way, the stress exerted on the outer part 51 by bending is alleviated, so that a material itself constituting the outer part 51 does not need to expand and contract. As a result, the battery 50 can be bent with a weak force without damaging the outer part 51.

[0373] As in Fig. 22D, when the battery 50 is bent, the positions of the positive electrode 11a and the negative electrode 11b are shifted relative to each other. At this time, the ends of the stacked positive electrodes 11a and the negative electrode 11b on the sealing portion 63 side are fixed by the fixing member 17. Thus, the plurality of positive electrodes 11a and the plurality of negative electrodes 11b are more shifted at a position closer to the bending portion 61. Therefore, the stress applied to the positive electrode 11a and the negative electrode 11b is alleviated, and the positive electrode 11a and the negative electrode 11b themselves do not need to expand and contract. As a result, the battery 50 can be bent without damaging the positive electrode 11a and the negative electrode 11b.

[0374] Furthermore, the space 73 is provided between the end portions of the positive and negative electrodes 11a and 11b and the outer part 51, whereby the relative positions of the positive electrode 11a and the negative electrode 11b can be shifted while the end portions of the positive electrode 11a and the negative electrode 11b, which are located on an inner side when the battery 50 is bent, do not contact the outer part 51.

[0375] In the Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D and Fig. 23A and Fig. In the battery 50 shown in Fig. 23B, even if the battery 50 is repeatedly bent and unbent or straightened, the outer part, the positive electrode 11a, and the negative electrode 11b are less likely to be damaged and the battery characteristics are less likely to deteriorate. When the positive electrode active material described in the above embodiment is used for the positive electrode 11a included in the battery 50, a battery with better cycle characteristics can be obtained. (Embodiment 4)

[0376] In this embodiment, examples of electrical devices including the secondary battery of one embodiment of the present invention will be described.

[0377] Show first Fig. 24A to Fig. 24G Examples of electrical devices incorporating the flexible secondary battery described in Embodiment 3. Examples of an electrical device incorporating a flexible secondary battery include televisions (also referred to as televisions or television receivers), monitors for computers or the like, digital cameras or digital video cameras, digital photo frames, mobile phones (also referred to as cellular phones or portable telephones), portable game consoles, portable information terminals, audio playback devices, and large-scale gaming machines such as pachinko machines.

[0378] In addition, a flexible secondary battery can be installed along a curved surface of an interior / exterior wall of a house or building or along a curved interior / exterior of a vehicle.

[0379] Fig. 24A illustrates an example of a mobile phone. A mobile phone 7400 is provided with a display section 7402 installed in a case 7401, an operation button 7403, an external connection terminal 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. When the secondary battery of one embodiment of the present invention is used as the secondary battery 7407, a lightweight mobile phone with a long service life can be provided.

[0380] Fig. 24B illustrates the mobile phone 7400 being bent. When the entire mobile phone 7400 is bent by external force, the secondary battery 7407 included in the mobile phone 7400 is also bent. Fig. Figure 24C illustrates the bent secondary battery 7407. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. Note that the secondary battery 7407 includes a terminal electrode 7408 electrically connected to a current collector 7409. The current collector 7409 is, for example, a copper foil and partially alloyed with gallium; therefore, the adhesion between the current collector 7409 and an active material layer in contact with the current collector 7409 is improved, and the secondary battery 7407 can have high reliability even in a bent state.

[0381] Fig. 24D illustrates an example of a wristband-type display device. A wearable display device 7100 includes a case 7101, a display section 7102, an operation button 7103, and a secondary battery 7104. Fig. Figure 24E illustrates the curved secondary battery 7104. When the curved secondary battery 7104 is worn on a user's arm, the casing changes its shape, and the curvature of part of the secondary battery 7104 or the entire secondary battery 7104 is changed. Note that the radius of curvature of a curve at a point denotes the radius of the circular arc closest to the curve at that point. The inverse of the radius of curvature is the curvature. Specifically, a part of the casing, the entire casing, a part of the main surface, or the entire main surface of the secondary battery 7104 is changed within the range of the radius of curvature of 40 mm to 150 mm. When the radius of curvature of the main surface of the secondary battery 7104 is greater than or equal to 40 nm and less than or equal to 150 nm, reliability can be maintained at a high level.When the secondary battery of one embodiment of the present invention is used as the secondary battery 7104, a lightweight portable display device with a long service life can be provided.

[0382] Fig. 24F illustrates an example of a wristwatch-type portable information terminal. A portable information terminal 7200 includes a case 7201, a display portion 7202, a band 7203, a buckle 7204, an operation button 7205, an input / output terminal 7206, and the like.

[0383] The portable information terminal 7200 can execute various applications, such as mobile phone calls, sending and receiving emails, displaying and editing texts, playing music, Internet communication, and a computer game.

[0384] The display surface of the display section 7202 is curved, and images can be displayed on the curved display surface. The display section 7202 further includes a touch sensor, and operations can be performed 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 section 7202.

[0385] The control button 7205 can perform various functions, such as setting the time, turning the power on / off, turning wireless communication on / off, enabling / disabling sleep mode, and enabling / disabling a power-saving mode. For example, the functions of the control button 7205 can be freely configured by configuring the operating system built into the portable information terminal 7200.

[0386] The portable information terminal 7200 can use short-range communication, which is a communication method based on an existing communication standard. For example, two-way communication can be performed between the portable information terminal 7200 and a headset capable of wireless communication, thus enabling hands-free calling.

[0387] The portable information terminal 7200 also includes the input / output port 7206, and data can be sent and received directly to and from another information terminal via a connector. Charging is also possible via the input / output port 7206. Note that charging can be performed without the input / output port 7206 by wireless power supply.

[0388] The display section 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. When the secondary battery of one embodiment of the present invention is used, a lightweight portable information terminal with a long service life can be provided. For example, the secondary battery 7104 shown in Fig. 24E and is in the bent state, in the housing 7201. Alternatively, the secondary battery 7104 shown in Fig. 24E, may be provided in the band 7203 such that it can be bent.

[0389] A portable information terminal 7200 preferably includes a sensor. As the sensor, a human body sensor, such as a fingerprint sensor, a pulse sensor, a temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like, is preferably mounted.

[0390] Fig. Figure 24G illustrates an example of a display device in the form of an armband. A display device 7300 includes a display section 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 may include a touch sensor in the display section 7304 and serve as a wearable information terminal.

[0391] The display surface of the display section 7304 is curved, and images can be displayed on the curved display surface. A display state of the display device 7300 can be changed, for example, through short-range communication, which is a communication method based on an existing communication standard.

[0392] The display device 7300 includes an input / output port, and data can be sent and received directly to and from another information terminal via a connector. Charging is also possible via the input / output port. Note that charging can be performed without the input / output port using wireless power supply.

[0393] When the secondary battery of one embodiment of the present invention is used as the secondary battery included in the display device 7300, a lightweight display device with a long service life can be provided.

[0394] Additionally show Fig. 24 hours, Fig. 25A to Fig. 25C and Fig. 26 examples of electrical appliances incorporating the secondary battery having excellent cycle characteristics described in the above embodiment.

[0395] When the secondary battery of one embodiment of the present invention is used as a secondary battery of a daily electrical appliance, a lightweight product with a long service life can be provided. Examples of daily electrical appliances include an electric toothbrush, an electric shaver, an electric beauty device, and the like. As secondary batteries for these products, small, rod-shaped, lightweight, and high-capacity secondary batteries are desired for ease of handling by users.

[0396] Fig. 24H is a perspective view of a device called an evaporator. In Fig. 24H, a vaporizer 7500 includes an atomizer 7501 with a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 containing a liquid supply bottle, a sensor, and the like. To improve safety, a protection circuit that prevents overcharging and overdischarging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 in Fig. 24H includes an output terminal for connecting to a charger. When the vaporizer 7500 is held by a user, the secondary battery 7504 becomes a tip portion; therefore, it is preferable that the secondary battery 7504 has a short overall length and is lightweight. With the secondary battery of one embodiment of the present invention, which has a high capacity and excellent cycle characteristics, the small and lightweight vaporizer 7500 that can be used for a long time can be provided.

[0397] Next, Fig. 25A and Fig. 25B shows an example of a foldable tablet computer. A tablet computer 9600, which is Fig. 25A and Fig. 25B includes a housing 9630a, a case 9630b, a movable part 9640 connecting the housings 9630a and 9630b, a display section 9631 including a display section 9631a and a display section 9631b, a display mode switching switch 9626, a power switch 9627, a power saving mode switching switch 9625, a bracket 9629, and an operation switch 9628. A flexible screen is used for the display section 9631, whereby a tablet computer with a larger display section can be provided. Fig. 25A illustrates the tablet computer 9600 being opened, and Fig. Figure 25B shows the 9600 tablet computer closed.

[0398] The tablet computer 9600 includes a power storage unit 9635 within the housings 9630a and 9630b. The power storage unit 9635 is provided across the movable part 9640 in the housings 9630a and 9630b.

[0399] Part of the display section 9631a may be a touchscreen area, and data can be input by touching a displayed operation button. Although a structure is shown as an example in which half of the display section 9631a has only a display function and the other half has a touchscreen function, the display section 9631a is not limited to this structure. The entire area of ​​the display section 9631a may have a touchscreen function. For example, the display section 9631a may display keyboard buttons on the entire area to serve as a touchscreen, and the display section 9631b may be used as a display screen.

[0400] A part of the display section 9631b may be a touchscreen area like the display section 9631a. A button for displaying / hiding a keyboard of the touchscreen is touched with a finger, a stylus, or the like, so that keyboard buttons can be displayed on the display section 9631b.

[0401] Touch input can be performed in the touchscreen areas and simultaneously.

[0402] The display mode switching switch 9626 enables switching between a portrait and landscape display, switching between a color display and a black and white display, and the like. The power saving mode switching switch 9625 can control the display luminance according to the amount of external light measured by an optical sensor in the tablet computer 9600 when using the tablet computer 9600. The tablet computer may include another sensing device, such as a sensor for detecting inclination, such as a gyroscope sensor or an acceleration sensor, in addition to the optical sensor.

[0403] Although in Fig. 25A, the display section 9631a and the display section 9631b have the same area, an embodiment of the present invention is not limited to this example. The display section 9631a and the display section 9631b may have different areas or different display qualities. For example, one display panel may display images with higher resolution than the other display panel.

[0404] The tablet computer is in Fig. 25B. The tablet computer includes the housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. The power storage unit of one embodiment of the present invention is used as the power storage unit 9635.

[0405] The tablet computer 9600 can be folded such that the casings 9630a and 9630b overlap when not in use. Therefore, the display sections 9631a and 9631b can be protected, increasing the durability of the tablet computer 9600. With the power storage unit 9635 including the secondary battery of one embodiment of the present invention, which has a high capacity and excellent cycle characteristics, the tablet computer 9600 that can be used for a long time can be provided.

[0406] The tablet computer that Fig. 25A and Fig. 25B may also have a function of displaying various types of data (e.g., a still image, a moving image, and a text image), a function of displaying a calendar, a date, or the time on the display section, a touch input function of operating or editing the data displayed on the display section by the touch input, a function of controlling processing by various types of software (programs), and the like.

[0407] The solar cell 9633, mounted on the surface of the tablet computer, supplies electrical power to a touchscreen, a display section, an image signal processing section, and the like. Note that the solar cell 9633 can be disposed on one or both surfaces of the casing 9630, and the power storage unit 9635 can be efficiently charged. Using a lithium-ion battery as the power storage unit 9635 offers advantages such as miniaturization.

[0408] The structure and function of the Fig. 25B, the charge / discharge control circuit 9634 will be described with reference to a block diagram in Fig. 25C. The solar cell 9633, the energy storage unit 9635, the DC-DC converter 9636, a converter 9637, switches SW1 to SW3 and the display section 9631 are shown in Fig. 25C, and the energy storage unit 9635, the DC-DC converter 9636, the converter 9637 and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 in Fig. 25B.

[0409] First, an example of operation in the case where power is generated from the solar battery 9633 using external light will be described. The voltage of the electric power generated by the solar cell is increased or decreased by the DC-DC converter 9636 to a charging voltage of the power storage unit 9635. When the power from the solar cell 9633 is used to drive the display section 9631, the switch SW1 is turned on, and the voltage of the power is increased or decreased by the converter 9637 to a voltage required to drive the display section 9631. When no display is performed on the display section 9631, the switch SW1 is turned off and the switch SW2 is turned on, so that the power storage unit 9635 can be charged.

[0410] Note that the solar cell 9633 is described as an example of a power generation means; however, an embodiment of the present invention is not limited to this example. The power storage unit 9635 may be charged using another power generation means, such as a piezoelectric element or a thermoelectric conversion element (Peltier element). For example, the power storage unit 9635 may be charged using a non-contact power transfer module that wirelessly (contactlessly) transmits and receives power to charge the battery, or in combination with another charging means.

[0411] Fig. 26 shows further examples of electrical devices. In Fig. 26, a display device 8000 is an example of an electrical device that includes a secondary battery 8004 of one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving a television broadcast and includes a housing 8001, a display section 8002, speaker sections 8003, the secondary battery 8004, and the like. The secondary battery 8004 of one embodiment of the present invention is provided in the housing 8001. The display device 8000 can receive electric power from a commercial power source. Alternatively, the display device 8000 can use electric power stored in the secondary battery 8004.Thus, the display device 8000 can be operated using the secondary battery 8004 of one embodiment of the present invention as an uninterruptible power source even when electric power cannot be supplied from a commercial power source due to a power outage or the like.

[0412] A semiconductor display device such as a liquid crystal display device, a light-emitting device in which a light-emitting element such as an organic EL element is provided in each pixel, an electrophoresis display device, a digital micromirror device (DMD), a plasma display panel (PDP), or a field emission display (FED) can be used for the display section 8002.

[0413] It should be noted that the display device in its category includes, in addition to a device for receiving a television broadcast, all information display devices for personal computers, advertisements and the like.

[0414] A built-in lighting device 8100 in Fig. Figure 26 is an example of an electrical device using a secondary battery 8103 of one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, the secondary battery 8103, and the like. Although Fig. 26 illustrates the case where the secondary battery 8103 is provided in a ceiling 8104 in which the housing 8101 and the light source 8102 are installed. The secondary battery 8103 may be provided in the housing 8101. The lighting device 8100 may receive electric power from a commercial power source. Alternatively, the lighting device 8100 may use electric power stored in the secondary battery 8103. Thus, the lighting device 8100 can be operated using the secondary battery 8103 of one embodiment of the present invention as an uninterruptible power source even when electric power from a commercial power source cannot be supplied due to a power outage or the like.

[0415] It should be noted that although the built-in lighting device 8100 provided in the ceiling 8104 is Fig. 26 as an example, the secondary battery of one embodiment of the present invention can be used, for example, as a built-in lighting device provided in a wall 8105, a floor 8106, a window 8107, or the like, in addition to the ceiling 8104. Alternatively, the secondary battery can be used in a table lamp or the like.

[0416] As the light source 8102, an artificial light source that artificially emits light using energy can be used. Specifically, an incandescent lamp, a discharge lamp such as a fluorescent lamp, and light-emitting elements such as an LED or an organic EL element are given as examples of the artificial light source.

[0417] An air conditioning system in Fig. Figure 26, which includes an indoor unit 8200 and an outdoor unit 8204, is an example of an electrical device including a secondary battery 8203 of one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, the secondary battery 8203, and the like. Although Fig. 26 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner may receive electric power from a commercial power source. Alternatively, the air conditioner may use electric power stored in the secondary battery 8203. Particularly, in the case where the secondary batteries 8203 are provided in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be operated using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power source even when electric power from a commercial power source cannot be supplied due to a power outage or the like.

[0418] It should be noted that although the split air conditioner, which includes the indoor unit and the outdoor unit, is used as an example in Fig. 26, however, the secondary battery of one embodiment of the present invention can be used in an air conditioner in which the functions of an indoor unit and an outdoor unit are integrated in one casing.

[0419] One in Fig. The electric freezer-refrigerator 8300 shown in Figure 26 is an example of an electrical appliance including a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric freezer-refrigerator 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, the secondary battery 8304, and the like. The secondary battery 8304 is mounted in the housing 8301. Fig. 26. The electric freezer-refrigerator 8300 can receive electrical power from a commercial power source. Alternatively, the electric freezer-refrigerator 8300 can use electrical power stored in the secondary battery 8304. Thus, the electric freezer-refrigerator 8300 can operate as an uninterruptible power source using the secondary battery 8304 of one embodiment of the present invention, even when electrical power from a commercial power source cannot be supplied due to a power outage or the like.

[0420] It should be noted that among the above-described electrical appliances, a high-frequency heating device such as a microwave oven and an electrical appliance such as an electric rice cooker require high power in a short time. The tripping of a circuit breaker of a commercial power source when using electrical appliances can be prevented by using the secondary battery of one embodiment of the present invention as an auxiliary power source to supply power that cannot be sufficiently supplied by a commercial power source.

[0421] In addition, during a period when electrical appliances are not used, especially when the proportion of the amount of energy actually consumed to the total amount of energy that can be supplied from a commercial power source (such a proportion is referred to as the energy consumption rate) is low, energy can be stored in the secondary battery, thereby reducing the energy consumption rate during a period when electrical appliances are used. For example, in the case of the electric freezer-refrigerator 8300, energy can be stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened and closed frequently.On the other hand, during the daytime when the temperature is high and the refrigerator door 8302 and the freezer door 8303 are frequently opened and closed, the secondary battery 8304 is used as an auxiliary power supply source; thus, the energy consumption rate during the daytime can be reduced.

[0422] According to one embodiment of the present invention, the secondary battery can have excellent cycle characteristics and improve reliability. Furthermore, according to one embodiment of the present invention, a high-capacity secondary battery can be obtained; thus, the secondary battery itself can be made more compact and lightweight due to improved characteristics of the secondary battery. Thus, the secondary battery of one embodiment of the present invention is used in the electrical device described in this embodiment, whereby a lighter electrical device with a longer service life can be obtained. This embodiment can be implemented in appropriate combination with any of the other embodiments. (Embodiment 5)

[0423] In this embodiment, examples of vehicles having the secondary battery of one embodiment of the present invention will be described.

[0424] The use of secondary batteries in vehicles enables the production of next-generation clean energy vehicles, such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs).

[0425] Fig. 27A to Fig. 27C each illustrates an example of a vehicle using the secondary battery of one embodiment of the present invention. A vehicle 8400 shown in Fig. 27A is an electric vehicle that runs using the drive power of an electric motor. Alternatively, the vehicle 8400 is a hybrid electric vehicle that can be suitably powered by either an electric motor or an internal combustion engine. An embodiment of the present invention can provide a high-mileage vehicle. The vehicle 8400 includes the secondary battery. As the secondary battery, the batteries described in Fig. 12C and Fig. 12D may be arranged in such a way that they are used in a floor part in the motor vehicle. Alternatively, a battery pack in which a plurality of secondary batteries, each arranged in Fig. 17A to Fig. 17C, are combined, arranged in a floor part of the vehicle. The secondary battery is used not only to drive an electric motor 8406, but also to supply electrical power to a light-emitting device, such as a headlight 8401 or an interior light (not shown).

[0426] The secondary battery can also supply electrical power to a display device of a speedometer, a tachometer, or the like in the vehicle 8400. Furthermore, the secondary battery can supply electrical power to a semiconductor device in the vehicle 8400, such as a navigation system.

[0427] Fig. 27B illustrates a vehicle 8500 including the secondary battery. The vehicle 8500 can be charged when the secondary battery is supplied with electrical energy via an external charger through a plug-in system, a contactless power supply system, or the like. Fig. 27B, secondary batteries 8024 and 8025 in the vehicle 8500 are charged by a ground-based charger 8021 via a cable 8022. During charging, a given method such as CHAdeMO (registered trademark) or Combined Charging System as a charging method, the standard of a connector, or the like may be appropriately used. The ground-based charger 8021 may be a charging station provided in a commercial establishment or a household power source. For example, by a plug-in technology, the secondary battery 8024 in the vehicle 8500 may be charged by supplying it with external electric power. Charging may be performed by converting an alternating current (AC electric power) into a direct current (DC electric power) using a converter such as an AC-DC converter.

[0428] Furthermore, although not shown, the vehicle may include a power receiving device so that it can be charged by supplying electric power from an overhead power transmission device in a contactless manner. In the case of the contactless power supply system, the electric vehicle can be charged not only while stationary but also while traveling by installing a power transmission device in a road or an exterior wall. Furthermore, the contactless power supply system can be used to transmit and receive electric power between vehicles. A solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stationary or moving. To supply electric power in such a contactless manner, an electromagnetic induction method or a magnetic resonance method may be used.

[0429] Fig. Figure 27C shows an example of a motorcycle using the secondary battery of one embodiment of the present invention. A scooter 8600 used in Fig. 27C includes a secondary battery 8602, side mirrors 8601, and turn signals 8603. The secondary battery 8602 can supply electrical power to the turn signals 8603.

[0430] Furthermore, in the Fig. In the scooter 8600 shown in Figure 27C, the secondary battery 8602 can be stored in a storage unit under the seat 8604. The secondary battery 8602 can be stored in the storage unit under the seat 8604 even with a small size. The secondary battery 8602 is detachable; thus, the secondary battery 8602 is brought inside for charging and stored before the motorcycle is driven.

[0431] According to one embodiment of the present invention, the secondary battery can have improved cycle characteristics, and the capacity of the secondary battery can be increased. Thus, the secondary battery itself can be made more compact and lightweight. The compact and lightweight secondary battery contributes to reducing the weight of a vehicle, and consequently, mileage increases. Furthermore, the secondary battery can be used in the vehicle as a power source for supplying electrical energy to products other than the vehicle. In such a case, for example, the use of a commercial power source during peak energy demand (power demand) times can be avoided. If the use of a commercial power source during peak energy demand times can be avoided, the avoidance can contribute to energy savings and a reduction in carbon dioxide emissions.In addition, if the cycle characteristics are excellent, the secondary battery can be used for a long period of time, thus reducing the amount of rare metals such as cobalt.

[0432] This embodiment can be implemented in suitable combination with the other embodiments. [Example 1]

[0433] In this example, the positive electrode active materials that are embodiments of the present invention are formed, and the observation results of the positive electrode active materials by STEM, the results of TEM images subjected to fast Fourier transformation, and the analysis results obtained by energy-dispersive X-ray spectroscopy (EDX) are described. Furthermore, the evaluation results of the properties of secondary batteries containing the positive electrode active materials are described. [Formation of a positive electrode active material]<<Probe 01> >

[0434] In this example, a positive electrode active material of Sample 01 was formed which contains lithium cobaltate as a composite oxide of lithium and a first transition metal contained in a first region, lithium titanate as an oxide of a second transition metal contained in a second region, and magnesium oxide as an oxide of a representative element contained in a third region.

[0435] In this example, lithium cobalt oxide particles (C-20F, manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.) were used as the starting material. Thus, steps 12 and 13 described in Embodiment 1 were omitted in this example. Note that the lithium cobalt oxide particles described above each have a particle diameter of approximately 20 μm and contain fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus within a range that can be analyzed by XPS.

[0436] Next, in step 14, the magnesium- and fluorine-containing lithium cobalt oxide particles were coated with a titanium-containing material using a sol-gel process. Specifically, TTIP was dissolved in isopropanol, and an isopropanol solution of TTIP was formed. Then, the lithium cobalt oxide particles were mixed into the solution so that the TTIP to magnesium- and fluorine-containing lithium cobalt oxide ratio was 0.01 ml / g.

[0437] The above-mixed solution was stirred with a magnetic stirrer at 25 °C for four hours at a humidity of 90% RH. During the process, water in one atmosphere and TTIP caused a hydrolysis and polycondensation reaction, and a titanium-containing layer formed on the surface of the magnesium and fluorine-containing lithium cobalt oxide particle.

[0438] The mixed solution, which had undergone the above process, was filtered to collect the residue. Kiriyama filter paper (No. 4) was used as the filter for filtration.

[0439] The collected residue was dried under vacuum at 70 °C for one hour.

[0440] Next, the lithium cobalt oxide particles coated with the titanium-containing material were heated. Heating was carried out using a muffle furnace under the following conditions: the dry air flow rate was 10 l / min; the temperature was 800 °C (temperature rise rate was 200 °C / h); and the residence time was two hours. The dew point of the dry air was preferably less than or equal to -109 °C.

[0441] The heated particles were then cooled to room temperature. The time required for the temperature to decrease from the retention temperature to room temperature was 10 to 15 hours. Afterward, a grinding treatment was performed. During the grinding treatment, the particles were passed through a sieve. The sieve had an opening width of 53 µm.

[0442] Finally, the cooled particles were collected and the positive electrode active material of Sample 01 was obtained. <<Probe 02> >

[0443] Sample 02 was formed as a comparative example by heating lithium cobalt oxide particles containing magnesium and fluorine without being coated with a titanium-containing material.

[0444] Lithium cobalt oxide particles manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. (product name: C-20F) were used as magnesium and fluorine-containing lithium cobalt oxide particles.

[0445] The magnesium and fluorine-containing lithium cobalt oxide particles were heated. The heating was carried out under the following conditions: the temperature was 800 °C (temperature rise rate was 200 °C / h); the residence time was two hours; and the oxygen flow rate was 10 l / min.

[0446] The heated particles were cooled and passed through a sieve as in Sample 01 to obtain a positive electrode active material of Sample 02.

[0447] It is likely that Sample 02 is a positive electrode active material containing lithium cobalt oxide inside and including a region containing magnesium in a surface portion. <<Probe 03> >

[0448] Sample 03 was formed as a comparative example in the following manner: A titanium-containing region was formed in the lithium cobalt oxide particles containing no magnesium by a sol-gel method, and then the lithium cobalt oxide particles were heated.

[0449] Lithium cobalt oxide particles manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. (product name: C-10N) were used. No magnesium was detected in the lithium cobalt oxide particles, and fluorine was detected at approximately 1 atomic % by XPS.

[0450] A titanium-containing region was formed in the lithium cobalt oxide particles by a sol-gel process, and the lithium cobalt oxide particles were dried, heated, cooled, and passed through a sieve as in Sample 01. The obtained lithium cobalt oxide particles were used as the positive electrode active material of Sample 03.

[0451] It is likely that Sample 03 is a positive electrode active material containing lithium cobalt oxide inside and including a region containing titanium in a surface portion. <<Probe 04> >

[0452] For Sample 04, lithium cobalt oxide particles were used as they are, without heating, as a comparative example.

[0453] Lithium cobalt oxide particles manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. (product name: C-10N) were used.

[0454] Sample 04 is a positive electrode active material that has no coating layer. <<Probe 05> >

[0455] For Sample 05, lithium cobalt oxide particles containing magnesium and fluorine were used as they are without heating as a comparative example.

[0456] Lithium cobalt oxide particles manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. (product name: C-20F) were used as magnesium and fluorine-containing lithium cobalt oxide particles. That is, Sample 05 was used in the same way as the starting material for Sample 01.

[0457] Table 1 shows the conditions of Sample 01 to Sample 05. [Table 1] Bedingungen Probe 01 LiCoO2+Mg+F, beschichtet mit einem Material, das Ti enthält, erwärmt Probe 02 LiCoO2+Mg+F, erwärmt Probe 03 LiCoO2, beschichtet mit einem Material, das Ti enthält, erwärmt Probe 04 LiCoO2, nicht erwärmt Probe 05 LiCoO2+Mg+F, nicht erwärmt [STEM]

[0458] The obtained positive electrode active material of Sample 01 was observed with an electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.) under the condition where the acceleration voltage was 200 kV. Fig. 28 shows the resulting electron microscope image. As in Fig. As shown in Figure 28, the positive electrode active material likely includes three different regions: the first region 101; the second region 102; and the third region 103. The third region 103 is observed as a region that is brighter than the first region 101 and the second region 102. Further, the crystal orientations of the first region 101 and the second region 102 are partially aligned with each other, and crystal orientations of the second region 102 and the third region 103 are partially aligned with each other. [STEM-FFT]

[0459] Fig. 29A1 shows a fast Fourier transform (FFT) image of a 103FFT area in the STEM image of Fig. 28. In Fig. 29A2 is a center point O of Fig. 29A1 is shown by a cross and bright points A, B and C are each surrounded by a circle. Similarly, Fig. 29B1 an FFT image of a 102FFT area. In Fig. 29B2 is a center point O of Fig. 29B1 is shown by a cross, and bright points A, B and C are each surrounded by a circle. In addition, Fig. 29C1 an FFT image of a region 101FFT. In Fig. 29C2 is a center point O of Fig. 29C1 is shown by a cross, and bright points A, B and C are each surrounded by a circle.

[0460] In Fig. 29A2, the distance d between the bright spot A and the center O is 0.256 nm, the distance d between the bright spot B and the center O is 0.241 nm, and the distance d between the bright spot C and the center O is 0.209 nm. Furthermore, ∠COA is 121°, ∠COB is 52°, and ∠AOB is 69°. Based on these results, the region 103FFT likely contains magnesium oxide (MgO, cubic crystal).

[0461] Similarly, in Fig. 29B2, the distance d between the bright spot A and the center O is 0.238 nm, the distance d between the bright spot B and the center O is 0.225 nm, and the distance d between the bright spot C and the center O is 0.198 nm. Furthermore, ∠COA is 123°, ∠COB is 52°, and ∠AOB is 71°. Based on these results, the region 102FFT likely contains lithium titanate (LiTiO2, cubic crystal).

[0462] In Fig. 29C2, the distance d between the bright spot A and the center O is 0.240 nm, the distance d between the bright spot B and the center O is 0.235 nm, and the distance d between the bright spot C and the center O is 0.196 nm. Furthermore, ∠COA is 126°, ∠COB is 52°, and ∠AOB is 74°. Based on these results, the region 101FFT likely contains lithium cobaltate (LiCoO2, rhombohedral). [EDX]

[0463] Fig. 30A1, Fig. 30A2, Fig. 30B1, Fig. 30B2, Fig. 30C1 and Fig. 30C2 shows a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image and EDX element distribution images of the positive electrode active material of Sample 01. Fig. 30A1 shows a HAADF-STEM image, Fig. 30A2 shows a distribution image of oxygen atoms, Fig. 30B1 shows a distribution image of cobalt atoms, Fig. 30B2 shows a distribution pattern of fluorine atoms, Fig. 30C1 shows a distribution image of titanium atoms, and Fig. Figure 30C2 shows a distribution image of magnesium atoms. It should be noted that in the EDX element distribution images in Fig. 30A2, Fig. 30B1, Fig. 30B2, Fig. 30C1 and Fig. 30C2 and Fig. 31A2, Fig. 31B1, Fig. 31B2, Fig. 31C1 and Fig. 31C2 an area where the number of elements is less than or equal to a lower measurement limit is displayed in white, and as the number of elements is increased, the white area turns black.

[0464] As in Fig. 30A2 and Fig. 30B1, it has been found that the oxygen atoms and the cobalt atoms are distributed throughout the positive electrode active material particle. In contrast, as shown in Fig. 30B2, Fig. 30C1 and Fig. 30C2, it has been found that the fluorine atoms, the titanium atoms and the magnesium atoms are unevenly distributed in a region near the surface of the positive electrode active material.

[0465] Show next Fig. 31A1, Fig. 31A2, Fig. 31B1, Fig. 31B2, Fig. 31C1 and Fig. 31C2 is a HAADF-STEM image and EDX element distribution images of the positive electrode active material of Sample 05, which is a comparative example. Fig. 31A1 shows a HAADF-STEM image, Fig. 31A2 shows a distribution image of oxygen atoms, Fig. 31B1 shows a distribution image of cobalt atoms, Fig. 31B2 shows a distribution pattern of fluorine atoms, Fig. 31C1 shows a distribution image of titanium atoms and Fig. 31C2 shows a distribution pattern of magnesium atoms.

[0466] As in Fig. 31B2 and Fig. 31C2, it has been found that even in Sample 05, which has not been heated, a certain amount of magnesium and fluorine is unevenly distributed in the vicinity of the surface. [EDX line analysis]

[0467] Fig. Figure 32 shows the results of TEM-EDX line analysis performed on a cross section of the vicinity of the surface of the positive electrode active material of Sample 01. Fig. Figure 32 is a graph showing data acquired along a line connecting the outside of the positive electrode active material of Sample 01 with the inside of the positive electrode active material. A distance of 0 nm indicates the outside of the positive electrode active material, and a distance of 14 nm indicates the inside of the particle. With EDX, the analysis range tends to be large, so elements can be detected not only in the center of an electron beam irradiation area, but also in the area around the center.

[0468] As in Fig. As shown in Figure 32, it was found that there are peaks of magnesium and titanium near the surface of the positive electrode active material of Sample 01, and the distribution of magnesium is closer to the surface than the distribution of titanium. It was also found that the peak of magnesium is closer to the surface than the peak of titanium. In addition, it is likely that cobalt and oxygen are present at the outermost surface of the positive electrode active material particle.

[0469] As in Fig. As shown in Figure 32, fluorine is barely detected. This is probably because fluorine, a light element, is difficult to detect with EDX.

[0470] From the above STEM images, FFT images, EDX element distribution images, and EDX line analysis, it was found that Sample 01 is a positive electrode active material of one embodiment of the present invention, which includes the first region containing lithium cobaltate, the second region containing lithium, titanium, cobalt, and oxygen, and the third region containing magnesium and oxygen. It was found that in Sample 01, part of the second region and part of the third region overlap.

[0471] In the graph of Fig. 32, the amount of oxygen detected is stable at a distance of 4 nm or more. Thus, in this example, the average value O ave of the amount of oxygen detected in the stable range, and it is assumed that a distance x of the measuring point at which the measured value is obtained is 0.5 O ave , ie the value of 50% of the average value O ave , closest to the surface of the positive electrode active material particle.

[0472] In this example, the average value is O ave the amount of oxygen detected in a range from a distance of 4 nm to a distance of 14 nm 674.2. The x-axis of the measurement point at which the closest measured value to 337.1, which is 50% of 674.2, is obtained, shows a distance of 1.71 nm. Thus, in this example, it is assumed that a distance of 1.71 nm in the graph of Fig. 32 corresponds to the surface of the positive electrode active material particle.

[0473] When the surface of the positive electrode active material particle in Fig. 32 is set to a distance of 1.71 nm, the magnesium peak and the titanium peak are present at 0.72 nm and 1.00 nm from the surface of the positive electrode active material particle, respectively.

[0474] The concentration of magnesium is greater than or equal to 1 / 5 of the peak from the surface of the positive electrode active material particle to a distance of 4.42 nm, that is, to a region of 2.71 nm from the surface. The measured value of magnesium is less than 1 / 5 of the peak at a distance of 4.57 nm or more, that is, at a depth of 2.86 nm or more from the surface of the positive electrode active material particle. Thus, it was found that in Sample 01, a region from the surface to a depth of 2.71 nm is the third region.

[0475] In addition, the concentration of titanium is higher than or equal to 1 / 2 of the peak from a distance of 2.14 nm to a distance of 3.42 nm. Thus, it is found that a region from a depth of 0.43 nm to a depth of 1.71 nm from the surface of the positive electrode active material particle is the second region.

[0476] Next, evaluation results of the charging and discharging characteristics of secondary batteries manufactured using the positive electrode active materials of Sample 01 to Sample 05 formed in the above manner will be described. [Manufacture of secondary batteries]

[0477] CR2032 type button cell secondary batteries (with a diameter of 20 mm and a height of 3.2 mm) were manufactured using the positive electrode active materials of Sample 01 to Sample 05 formed in the above manner.

[0478] A positive electrode formed by applying a slurry was used in which a positive electrode active material (LCO), acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 95:2.5:2.5 to form a current collector.

[0479] A lithium metal was used as the counter electrode.

[0480] As the electrolyte contained in an electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiPF6) was used, and as the electrolyte solution, a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 3:7 and vinylene carbonate (VC) was used at 2 wt%.

[0481] A positive electrode can and a negative electrode can were made of stainless steel (SUS). [Evaluation of charging and discharging characteristics]

[0482] Next, the charging and discharging characteristics of the secondary batteries of Sample 01 and Sample 05 formed as above were evaluated. The measurement temperature was 25 °C. Twenty charging and discharging cycles were performed at 4.6 V (CCCV, 0.5 C, cutoff current of 0.01 C) and 2.5 V (CC, 0.5 C), respectively. Here, 1 C was set to 137 mA / g, which was a current value per weight of the positive electrode active material.

[0483] Fig. 33 is a graph showing the charging and discharging characteristics of the secondary battery using the positive electrode active material of Sample 01. Fig. 33 shows excellent charge and discharge characteristics with a broad plateau. Furthermore, the results of the 20 charge and discharge cycles almost overlap, indicating excellent cycling characteristics.

[0484] Fig. Figure 34 is a graph showing the charge and discharge characteristics of the secondary battery of Sample 05, which is a comparative example. Excellent charge and discharge characteristics are shown in the initial cycles; as indicated by arrows in Fig. However, as shown in Figure 34, the charging capacity and discharging capacity decrease with increasing cycles. [Evaluation of cycle properties]<<Aufladen bei 4,4 V> >

[0485] The cycling characteristics of Sample 01 and Sample 05 secondary batteries charged at 4.4 V were evaluated. The measurement temperature was 25 °C. Charging was performed at 4.4 V (CCCV, 0.5 C, cut-off current of 0.01 C) and discharging was performed at 2.5 V (CC, 0.5 C).

[0486] Fig. Figure 35 is a graph showing the cycle characteristics of the secondary batteries charged at 4.4 V. In Fig. 35, a solid line and a dashed line indicate secondary batteries containing the positive electrode active materials of Sample 01 and Sample 05, respectively. As shown in Fig. As shown in Figure 35, in the secondary battery containing Sample 01, the energy density retention rate was 99.5% even after 50 charge and discharge cycles, demonstrating extremely excellent cycling characteristics. In the secondary battery containing Sample 05, the energy density retention rate after 50 cycles was 94.3%. <<Aufladen bei 4,6 V> >

[0487] The cycling characteristics of secondary batteries Sample 01 to Sample 04 charged at 4.6 V were evaluated. The measurement temperature was 25 °C. Charging was performed at 4.6 V (CCCV, 0.5 C, cut-off current of 0.01 C), and discharging was performed at 2.5 V (CC, 0.5 C).

[0488] Fig. 36 is a graph showing the cycle characteristics charged at 4.6 V. As in Fig. As shown in Figure 36, in the secondary battery containing Sample 01, which is the positive electrode active material of one embodiment of the present invention, an energy density retention rate is 94.1% even after 50 charge and discharge cycles were performed at a high voltage of 4.6V, demonstrating very excellent cycle characteristics. On the other hand, the secondary batteries containing the positive electrode active materials of Sample 02, Sample 03, and Sample 04, which are comparative examples, are inferior to that of Sample 01, and in Sample 04, for example, the energy density retention rate after 50 cycles was 33.2%.

[0489] As described above, it has been found that the positive electrode active material having the structure of one embodiment of the present invention can achieve an advantageous effect when charging and discharging are performed at a voltage higher than 4.4 V. [Example 2]

[0490] In this example, the positive electrode active materials that are embodiments of the present invention are formed, and analysis results different from those in Example 1 are described. Furthermore, evaluation results of the properties of secondary batteries containing the positive electrode active materials under conditions different from those in Example 1 are described.

[0491] In this example, a positive electrode active material was formed containing lithium cobaltate as a composite oxide of lithium and a first transition metal contained in a first region, lithium titanate as an oxide of a second transition metal contained in a second region, and magnesium oxide as an oxide of a representative element contained in a third region. [Formation of a positive electrode active material and production of a secondary battery]<<Probe 06 und Probe 07> >

[0492] In this example, lithium cobalt oxide particles (C-20F, manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.) were used as the starting material.

[0493] Next, in step 14, the lithium cobalt oxide particles were coated with titanium oxide using a sol-gel process and dried. Step 14 was performed in a similar manner to Example 1, except that the mixing was performed such that the TTIP to lithium cobalt oxide ratio was 0.004 ml / g. The lithium cobalt oxide particles coated with titanium oxide and not yet heated are referred to as Sample 06.

[0494] Next, Sample 06, which consists of titanium oxide-coated lithium cobalt oxide particles, was heated. Heating was carried out using a muffle furnace in an oxygen atmosphere at 800 °C under the following conditions: a residence time of two hours and an oxygen flow rate of 10 l / min.

[0495] The particles were then cooled and collected as in Example 1 to obtain the positive electrode active material. The heated positive electrode active material is referred to as Sample 07. [TEM-EDX]

[0496] Sample 06 and Sample 07, especially cracks generated in the particles and the proximity of the cracks, were subjected to TEM-EDX analysis.

[0497] First, results of the TEM-EDX plane analysis of titanium in Fig. 37A, Fig. 37B1, Fig. 37B2, Fig. 37C1, Fig. 37C2, Fig. 37D1, Fig. 37D2, Fig. 37E1 and Fig. 37E2 and Fig. 38A, Fig. 38B1, Fig. 38B2, Fig. 38C1, Fig. 38C2, Fig. 38D1, Fig. 38D2, Fig. 38E1 and Fig. 38E2 shown.

[0498] Fig. 37A, Fig. 37B1, Fig. 37B2, Fig. 37C1, Fig. 37C2, Fig. 37D1, Fig. 37D2, Fig. 37E1 and Fig. 37E2 shows TEM-EDX analysis results of sample 06 before heating. Fig. Figure 37A is a cross-sectional TEM image showing the particle surfaces and crack sections. Fig. 37B1 and Fig. 37B2 show a HAADF-STEM image and a Ti distribution image of a region containing the surface of the particle and in Fig. 37A is marked with a circle marked "1". Similarly, Fig. 37C1 and Fig. 37C2 a HAADF-STEM image and a Ti distribution image of an area at a depth of approximately 20 nm from the surface in the crack section shown in Fig. 37A is marked with a circle marked with "2". Fig. 37D1 and Fig. 37D2 show a HAADF-STEM image and a Ti distribution image of a region at a depth of approximately 500 nm from the surface in the crack section formed in Fig. 37A is marked with a circle marked with "3". Fig. 37E1 and Fig. 37E2 show a HAADF-STEM image and a Ti distribution image of a region at a depth of approximately 1000 nm from the surface in the crack section formed in Fig. 37A is marked with a circle marked with "4". It should be noted that in EDX element distribution images in Fig. 37A, Fig. 37B1, Fig. 37B2, Fig. 37C1, Fig. 37C2, Fig. 37D1, Fig. 37D2, Fig. 37E1 and Fig. 37E2, Fig. 38A, Fig. 38B1, Fig. 38B2, Fig. 38C1, Fig. 38C2, Fig. 38D1, Fig. 38D2, Fig. 38E1 and Fig. 38E2, Fig. 39A, Fig. 39B1, Fig. 39B2, Fig. 39C1, Fig. 39C2, Fig. 39D1, Fig. 39D2, Fig. 39E1 and Fig. 39E2 and Fig. 40A, Fig. 40B1, Fig. 40B2, Fig. 40C1, Fig. 40C2, Fig. 40D1, Fig. 40D2, Fig. 40E1 and Fig. 40E2 an area where the number of elements is less than or equal to a lower measurement limit is shown in white, and as the number of elements is increased, the white area turns black.

[0499] Fig. 38A, Fig. 38B1, Fig. 38B2, Fig. 38C1, Fig. 38C2, Fig. 38D1, Fig. 38D2, Fig. 38E1 and Fig. 38E2 shows TEM-EDX analysis results of sample 07 after heating. Fig. Figure 38A is a cross-sectional TEM image showing the particle surfaces and crack sections. Fig. 38B1 and Fig. 38B2 show a HAADF-STEM image and a Ti distribution image of a region containing the surface of the particle and in Fig. 38A is marked with a circle marked "1". Similarly, Fig. 38C1 and Fig. 38C2 a HAADF-STEM image and a Ti distribution image of an area at a depth of approximately 20 nm from the surface in the crack section shown in Fig. 38A is marked with a circle marked with "2". Fig. 38D1 and Fig. 38D2 show a HAADF-STEM image and a Ti distribution image of a region at a depth of approximately 500 nm from the surface in the crack section formed in Fig. 38A is marked with a circle marked with "3". Fig. 38E1 and Fig. 38E2 show a HAADF-STEM image and a Ti distribution image of a region at a depth of approximately 1000 nm from the surface in the crack section formed in Fig. 38A is marked with a circle marked with "4".

[0500] As in Fig. 37A, Fig. 37B1, Fig. 37B2, Fig. 37C1, Fig. 37C2, Fig. 37D1, Fig. 37D2, Fig. 37E1 and Fig. 37E2 and Fig. 38A, Fig. 38B1, Fig. 38B2, Fig. 38C1, Fig. 38C2, Fig. 38D1, Fig. 38D2, Fig. 38E1 and Fig. As shown in Figure 38E2, in Sample 06, segregation of titanium is observed on the particle surfaces before heating; however, no segregation is observed in the crack section. In contrast, in Sample 07, segregation of titanium is observed both on the particle surfaces and in the crack section after heating. This means that it was found that titanium was segregated on the surface of the crack section due to heating.

[0501] Next, results of the TEM-EDX plane analysis of magnesium in Fig. 39A, Fig. 39B1, Fig. 39B2, Fig. 39C1, Fig. 39C2, Fig. 39D1, Fig. 39D2, Fig. 39E1 and Fig. 39E2 and Fig. 40A, Fig. 40B1, Fig. 40B2, Fig. 40C1, Fig. 40C2, Fig. 40D1, Fig. 40D2, Fig. 40E1 and Fig. 40E2 shown.

[0502] Fig. Figure 39A is a cross-sectional TEM image of Sample 06, which is the same as Fig. 37A is. Fig. 39B1, Fig. 39C1, Fig. 39D1 and Fig. 39E1 are HAADF-STEM images taken with Fig. 37B1, Fig. 37C1, Fig. 37D1 and Fig. 37E1 are identical. Fig. 39B2 shows a Mg distribution pattern of an area that is the same as Fig. 39B1 is. Fig. 39C2 shows a Mg distribution pattern of an area that is the same as Fig. 39C1 is. Fig. 39D2 shows a Mg distribution pattern of an area that is the same as Fig. 39D1 is. Fig. 39E2 shows a Mg distribution pattern of an area that is the same as Fig. 39E1 is.

[0503] Fig. Figure 40A is a cross-sectional TEM image of sample 07, which is the same as Fig. 38A is. Fig. 40B1, Fig. 40C1, Fig. 40D1 and Fig. 40E1 are HAADF-STEM images that have the same Fig. 38B1, Fig. 38C1, Fig. 38D1 and Fig. 38E1 are. Fig. 40B2 shows a Mg distribution pattern of an area that is the same as Fig. 40B1 is. Fig. 40C2 shows a Mg distribution pattern of an area that is the same as Fig. 40C1 is. Fig. 40D2 shows a Mg distribution image of an area that is the same as Fig. 40D1 is. Fig. 40E2 shows a Mg distribution pattern of an area that is the same as Fig. 40E1 is.

[0504] As in Fig. 39A, Fig. 39B1, Fig. 39B2, Fig. 39C1, Fig. 39C2, Fig. 39D1, Fig. 39D2, Fig. 39E1 and Fig. 39E2 and Fig. 40A, Fig. 40B1, Fig. 40B2, Fig. 40C1, Fig. 40C2, Fig. 40D1, Fig. 40D2, Fig. 40E1 and Fig. As shown in Figure 40E2, in Sample 06, segregation of magnesium is not observed at the particle surfaces or in the crack section before heating. In contrast, in Sample 07, segregation of magnesium is observed both at the particle surfaces and in the crack section after heating.

[0505] To quantify titanium and magnesium, EDX spot analysis was performed on the areas formed by Fig. 37A with 1 to 6 marked circles, and carried out on the areas indicated by Fig. 38A, circles marked 1 to 6 are shown. Two points were measured in each area.

[0506] Fig. 41A and Fig. 41B shows EDX spot analysis results in an atomic ratio of titanium to cobalt. Fig. Figure 41A shows the results of sample 06 before heating. The acquisition points 1 to 6 in Fig. 41A correspond to the areas covered by Fig. 37A with circles marked 1 to 6. Fig. Figure 41B shows the results of sample 07 after heating. The detection points 1 to 6 in Fig. 41B correspond to the areas covered by Fig. 38A with circles marked 1 to 6.

[0507] As in Fig. 41A and Fig. As shown in Figure 41B, Ti / Co in the crack portion of Sample 06 is less than or equal to 0.01 at every measurement point; in contrast, the amount of titanium in the crack portion of Sample 07 is increased at many points, and there are measurement points where Ti / Co is greater than or equal to 0.05. Furthermore, Ti / Co at / in the particle surfaces of Sample 07 is between 0.10 and 0.18.

[0508] Show next Fig. 42A and Fig. 42B Results of EDX spot analysis in an atomic ratio of magnesium to cobalt. The detection points are the same as those in Fig. 41A and Fig. 41B.

[0509] As in the Fig. 42A and Fig. As shown in Figure 42B, the Mg / Co ratio in Sample 06 is less than or equal to 0.03 at both the particle surfaces and the crack section. In contrast, in Sample 07, there are many points where the amount of magnesium is increased both at the particle surfaces and in the crack section. Furthermore, the Mg / Co ratio at / in the particle surfaces is between 0.15 and 0.50, and that in the crack section is between 0 and 0.22.

[0510] Next, CR2032 button cell secondary batteries were fabricated using the positive electrode active material of Sample 07 after heating. A positive electrode formed by applying a slurry in which a positive electrode active material (LCO) of Sample 02, AB, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 95:3:2 to form a positive electrode current collector was used. A 20 μm thick aluminum foil was used as the positive electrode current collector. The amount of the positive electrode active material layer containing the positive electrode active material, AB, and PVDF was 7.6 mg / cm³. 2 .

[0511] A lithium metal was used as the counter electrode.

[0512] An electrolyte solution was used which was prepared by dissolving 1 mol / L LiPF6 in a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 3:7, and adding vinylene carbonate (VC) to the solution at 2 wt%. [Initial properties, rate properties]

[0513] Initial characteristics and rate characteristics of the secondary battery using the positive electrode active material of Sample 07 formed in the above manner were measured.

[0514] When measuring the initial properties, charging was performed at CCCV, 0.2 C, 4.6 V, and a cutoff current of 0.05 C, and discharging was performed at CC, 0.2 C, and a cutoff voltage of 3.0 V. Here, 1 C was set to 160 mA / g, which was a current value per weight of the positive electrode active material. The measurement temperature was 25 °C. Table 2 shows the measurement results of the initial properties. [Table 2] initial charging capacity [mAh / g] initial discharge capacity [mAh / g] initial charging and discharging efficiency [%] 221,2 217,5 98,3

[0515] The rate characteristics were measured after the initial characteristics were measured. The measurement was performed by changing the discharge rate in the following order: 0.2 C charge / 0.2 C discharge; 0.2 C charge / 0.5 C discharge; 0.2 C charge / 1.0 C discharge; 0.2 C charge / 2.0 C discharge; 0.2 C charge / 3.0 C discharge; 0.2 C charge / 4.0 C discharge; and 0.2 C charge / 5.0 C discharge. Note that the conditions except for the discharge rate were the same as those used for measuring the initial characteristics. The measurement temperature was 25 °C.

[0516] Table 3 shows the measurement results of the initial properties and the rate properties. In addition, Fig. 43 discharge curves of the rates. [Table 3] Rate [C] Discharge capacity [mAh / g] Discharge capacity retention rate % 0,2 218,2 100,0 0,5 215,8 98,9 1,0 213,1 97,7 20 207,9 95,3 3,0 204,0 93,5 4,0 198,8 91,1 5,0 184,3 84,5 [Temperature properties]

[0517] Next, a cell was fabricated under conditions similar to those of a cell for evaluating rate characteristics, except that the amount of the positive electrode active material layer was 8.2 mg / cm 2 was, and the temperature characteristics were measured. Charging was performed at 25°C, CCCV, 0.2°C, 4.6V, and a cutoff current of 0.05°C. Discharging was performed at 25°C, 0°C, -10°C, -20°C, and 45°C in that order, CC, 0.2°C, and a cutoff voltage of 3.0V. Fig. 44 shows measurement results of temperature properties. [Cycle properties]

[0518] Next, a cell was fabricated under conditions similar to those used for measuring temperature characteristics, and the cycling characteristics were measured. When measuring cycling characteristics, charging was performed at CCCV, 1.0 C, 4.55 V, and a cutoff current of 0.05 C, and discharging was performed at CC, 1.0 C, and a cutoff voltage of 3.0 V. The cycling characteristics were measured at a temperature of 45 °C, and 100 cycles were measured. The discharge capacity retention rate after 100 cycles was 86%. Fig. Figure 45 is a graph showing the discharge capacity retention rate of the measured cycle characteristics.

[0519] As can be seen from the measurement results, the specific surface area of ​​the positive electrode active material of sample 07 was 0.13 m 2 / G.

[0520] Furthermore, as can be seen from the measurement results of the particle size distribution of the positive electrode active material of Sample 07, the average particle diameter was 21.5 µm, 10%D was 13.1 µm, 50%D was 22.0 µm, and 90%D was 34.4 µm.

[0521] The tap density of the positive electrode active material of Sample 07 is 2.21 g / cm 3 . The tap density was measured using MULTI TESTER MT-1000 (manufactured by SEISHIN ENTERPRISE Co., Ltd.).

[0522] As described above, it has been found that the positive electrode active material of Sample 07, which is an embodiment of the present invention, exhibits excellent initial charge and discharge capacity, rate characteristics, and cycle characteristics. In particular, the initial charge and discharge capacity is high, i.e., 98% or higher; therefore, it is likely to inhibit side reactions. Furthermore, even at a high discharge rate of 2C, an excellent capacity of 96.1% is demonstrated using 0.2C as a reference. [Example 3]

[0523] In this example, a positive electrode active material comprising a region containing titanium and magnesium in a surface portion was formed by changing the ratio of Li to the first transition metal of the starting materials, and evaluation results of the properties are shown. [Formation of a positive electrode active material]

[0524] In this example, positive electrode active materials of Samples 11 to 17, Samples 21 to 28, and Samples 31 to 40 were prepared using cobalt as the first transition metal. The formation methods and conditions of these samples are as follows. <<Proben 11 bis 17> >

[0525] First, a lithium source, a cobalt source, a magnesium source, and a fluorine source, which would serve as starting materials, were weighed individually. In this example, lithium carbonate, cobalt oxide, magnesium oxide, and lithium fluoride were used as the lithium source, cobalt source, magnesium source, and fluorine source, respectively.

[0526] At this time, the starting materials of Sample 11 were weighed such that the ratio of Li to Co was 1.00. The starting materials of Sample 12 were weighed such that the ratio of Li to Co was 1.03. The starting materials of Sample 13 were weighed such that the ratio of Li to Co was 1.05. The starting materials of Sample 14 were weighed such that the ratio of Li to Co was 1.06. The starting materials of Sample 15 were weighed such that the ratio of Li to Co was 1.07. The starting materials of Sample 16 were weighed such that the ratio of Li to Co was 1.08. The starting materials of Sample 17 were weighed such that the ratio of Li to Co was 1.13.

[0527] In addition, the starting materials of each of Samples 11 to 17 were weighed such that when the number of cobalt atoms contained in the starting materials was set to 1, the number of magnesium atoms was 0.01, and the number of fluorine atoms was 0.02.

[0528] Next, the weighed starting materials for each sample were mixed separately using a ball mill.

[0529] The mixed raw materials were then baked. Baking was carried out at 1000 °C for 10 hours under the following conditions: the temperature rise rate was 200 °C / h; and the dry air flow rate was 10 l / min.

[0530] Through the above process, particles of a composite oxide containing lithium, cobalt, fluorine and magnesium were synthesized.

[0531] Next, TTIP was added to 2-propanol so that the amount of TTIP per weight of the positive electrode active material was 0.01 ml / g, and then mixing was performed to form a 2-propanol solution of tetra-i-propoxytitanium.

[0532] To the 2-propanol solution of TTIP, the particles of a composite oxide containing lithium, cobalt, fluorine and magnesium were added and then mixed.

[0533] The mixed solution described above was stirred with a magnetic stirrer for four hours at 25 °C and a humidity of 90% RH. During the process, water in one atmosphere and TTIP caused a hydrolysis and polycondensation reaction, and a titanium-containing layer formed on the surface of the magnesium and fluorine-containing lithium cobalt oxide particle.

[0534] The mixed solution, which had undergone the above process, was filtered to collect the residue. Kiriyama filter paper (No. 4) was used as the filter for filtration.

[0535] The collected residue was dried under vacuum at 70 °C for one hour.

[0536] The dried particles were heated. The heating was carried out in an oxygen atmosphere under the following conditions: the temperature was 800 °C (the temperature rise rate was 200 °C / h); and the residence time was two hours.

[0537] The heated particles were cooled and subjected to a comminution treatment. During the comminution treatment, the particles were passed through a sieve with an opening width of 53 µm.

[0538] The particles subjected to crushing treatment were used as positive electrode active materials of Samples 11 to 17. <<Proben 21 bis 27> >

[0539] The starting materials of Samples 21 to 27 were the same as those of Samples 11 to 16. At this time, the starting materials of Sample 21 were weighed such that the ratio of Li to Co was 1.00. The starting materials of Sample 22 were weighed such that the ratio of Li to Co was 1.03. The starting materials of Sample 23 were weighed such that the ratio of Li to Co was 1.05. The starting materials of Sample 24 were weighed such that the ratio of Li to Co was 1.06. The starting materials of Sample 25 were weighed such that the ratio of Li to Co was 1.07. The starting materials of Sample 26 were weighed such that the ratio of Li to Co was 1.08. The starting materials of Sample 27 were weighed such that the ratio of Li to Co was 1.13.

[0540] Samples 21 to 27 were prepared in a similar manner to Samples 11 to 17, except that the concentration of TTIP in the 2-propanol solution was adjusted so that the amount of TTIP per weight of the positive electrode active material was 0.02 ml / g. <<Probe 28> >

[0541] The ratio of Li to Co of the starting materials and the amount of TTIP of Sample 28 were equal to the ratio of Li to Co of the starting materials and the amount of TTIP of Sample 23. That is, in Sample 28, the starting materials were weighed such that the ratio of Li to Co was 1.05 and the amount of TTIP per weight of the positive electrode active material was 0.02 ml / g.

[0542] It should be noted that in Sample 28, after mixing the starting materials, baking was carried out at 950 °C.

[0543] Sample 28 was prepared in a similar manner to Sample 23, except for the baking temperature.

[0544] It is likely that Samples 11 to 17 and Samples 21 to 28 are each a positive electrode active material containing lithium cobaltate inside and containing a region containing titanium and magnesium in a surface portion. <<Proben 31 bis 40> >

[0545] Samples 31 to 40 were designed as comparative examples, none of which contained a region containing titanium.

[0546] The starting materials of sample 31 were weighed such that the ratio of Li to Co was 1.00. The starting materials of sample 32 were weighed such that the ratio of Li to Co was 1.01. The starting materials of sample 33 were weighed such that the ratio of Li to Co was 1.02. The starting materials of sample 34 were weighed such that the ratio of Li to Co was 1.03. The starting materials of sample 35 were weighed such that the ratio of Li to Co was 1.035. The starting materials of sample 36 were weighed such that the ratio of Li to Co was 1.04. The starting materials of sample 37 were weighed such that the ratio of Li to Co was 1.051. The starting materials of sample 38 were weighed such that the ratio of Li to Co was 1.061. The starting materials of sample 39 were weighed such that the ratio of Li to Co was 1.081.The starting materials of sample 40 were weighed such that the ratio of Li to Co was 1.130.

[0547] In addition, the starting materials of each of samples 31 to 40 were weighed so that when the number of cobalt atoms contained in the starting materials was set to 1, the number of magnesium atoms was 0.01, and the number of fluorine atoms was 0.02.

[0548] Next, the weighed starting materials for each sample were mixed separately using a ball mill.

[0549] The mixed raw materials were then baked. Baking was carried out at 1000 °C for 10 hours under the following conditions: the temperature rise rate was 200 °C / h; and the dry air flow rate was 10 l / min.

[0550] Through the above process, particles of a composite oxide containing lithium, cobalt, fluorine and magnesium were synthesized.

[0551] The synthesized particles were cooled and then heated. Heating was carried out in an oxygen atmosphere under the following conditions: the temperature was 800 °C (temperature rise rate was 200 °C / h), and the residence time was two hours.

[0552] The heated particles were cooled and subjected to a comminution treatment. During the comminution treatment, the particles were passed through a sieve with an opening width of 53 µm.

[0553] The particles subjected to crushing treatment were used as positive electrode active materials of Samples 31 to 40.

[0554] Table 4 shows the formation conditions of samples 11 to 17, samples 21 to 28 and samples 31 to 40. [Table 4] Li / Co TTIP Baking temperature Sample 11 1,00 0.01 ml / g 1000 °C Sample 12 1,03 Sample 13 1,05 Sample14 1,06 Sample15 1,07 Sample 16 1,08 Sample17 1,13 Sample 21 1,00 0.02 ml / g 1000 °C Sample 22 1,03 Sample 23 1,05 Sample 24 1,06 Sample 25 1,07 Sample 26 1,08 Sample 27 1,13 Sample 28 1,05 0.02 ml / g 950 °C Sample 31 1,00 - 1000 °C Sample 32 1,01 Sample 33 1,02 Sample 34 1,03 Sample 35 1,035 Sample 36 1,04 Sample 37 1,051 Sample 38 1,061 Sample 39 1,081 Sample 40 1,130 [XPS]

[0555] The positive electrode active materials of samples 11 to 17, samples 21 to 28, and samples 31 to 40 were subjected to XPS analysis. Table 5 shows the XPS analysis results of samples 11 to 17, Table 6 shows the XPS analysis results of samples 21 to 28, and Table 7 shows the XPS analysis results of samples 31 to 40. Tables 5 to 7 show the relative concentration values ​​of each element under the condition that the cobalt concentration is 1. [Table 5] [Table 6] [Table 7] relative value under the condition that the concentration of Co is 1 Li / Co Li Co O C F Mg Ca N / a Sample 31 1,00 0,51 1,00 2,45 0,69 0,08 0,27 0,03 0,08 Sample 32 1,01 0,67 1,00 2,65 0,77 0,08 0,28 0,03 0,08 Sample 33 1,02 0,53 1,00 2,51 0,66 0,09 0,27 0,02 0,06 Sample 34 1,03 0,79 1,00 2,93 0,92 0,09 0,35 0,04 0,14 Sample 35 1,04 0,65 1,00 2,33 0,48 0,11 0,32 0,03 0,11 Sample 36 1,04 0,69 1,00 2,73 0,56 0,11 0,38 0,05 0,16 Sample 37 1,05 0,67 1,00 3,04 0,64 0,09 0,35 0,04 0,21 Sample 38 1,06 0,83 1,00 2,65 1,03 0,29 0,10 0,05 0,11 Sample 39 1,08 0,80 1,00 2,79 1,04 0,26 0,03 0,08 0,10 Sample 40 1,13 0,77 1,00 2,72 0,22 0,99 0,00 0,01 0,26

[0556] Fig. 46A and Fig. 46B are graphs in which the relative value of magnesium and the relative value of titanium are extracted from the analysis results of Tables 5 to 7. Fig. Figure 46A is a graph showing the ratio of Li to Co and the relative value of magnesium. Fig. Figure 46B is a graph showing the ratio of Li to Co and the relative value of titanium.

[0557] From the analysis results of samples 31 to 40 in Fig. 46A shows that in the case where no titanium-containing coating layer is included, the magnesium concentration is high in samples where the Li to Co ratio is greater than or equal to 1.00 and less than or equal to 1.05. This is likely because the magnesium contained in the raw materials is segregated by heating in a range where the element concentration can be detected by XPS. In contrast, in samples where the Li to Co ratio is greater than or equal to 1.06, the magnesium concentration is low; therefore, it is likely that magnesium segregation does not easily occur when the amount of lithium is too large.

[0558] From the analysis results of samples 11 to 16 and samples 21 to 26 in Fig. 46A, it has been found that the concentration of magnesium in a region where the element concentration can be detected by XPS is higher in the case where a region containing titanium is included in a surface portion than in the case where the region containing titanium is not included.

[0559] Furthermore, in the case where the ratio of Li to Co is 1.06, in the samples where the titanium-containing region is not included, the concentration of magnesium is low in a region where the element concentration can be detected by XPS; in contrast, in the samples where the titanium-containing region is included, the concentration of magnesium is high in a region where the element concentration can be detected by XPS. That is, when the titanium-containing region is formed in the surface portion, magnesium is sufficiently segregated even if the ratio of Li to Co is high.

[0560] It should be noted that even when the titanium-containing region is included, the magnesium concentration is lower in the case where the Li to Co ratio is 1.07 than in the case where the Li to Co ratio is 1.06. Furthermore, in the case where the Li to Co ratio is greater than or equal to 1.08, the segregation of magnesium is likely not to occur easily even when the titanium-containing region is included. [Evaluation of cycle properties]< <energiedichte-retentionsrate>>

[0561] Next, the cycle characteristics were evaluated in a similar manner as in Example 1 using the positive electrode active materials of Samples 11 to 14, Sample 16, Samples 21 to 24, and Sample 26.

[0562] The shape of the secondary battery, the materials and mixing ratios of the positive electrode active material, the conductive additive and the binder in the positive electrode, the counter electrode, the electrolyte solution, the outer part, the cycle property test conditions, and the like are the same as in Example 1.

[0563] Fig. 47A is a graph showing the energy density retention rates and the number of charge and discharge cycles at the time of charging at 4.6 V of secondary batteries using the positive electrode active materials of Samples 11 to 14 and Sample 16, which were formed such that the amount of TTIP per weight of the positive electrode active material was 0.01 ml / g. Fig. 47B is a graph showing the energy density retention rates and the number of charge and discharge cycles at the time of charging at 4.6 V of secondary batteries using the positive electrode active materials of Samples 21 to 24 and Sample 26, which were formed such that the amount of TTIP per weight of the positive electrode active material was 0.02 ml / g.

[0564] As in Fig. As shown in Figure 47A, in the case where TTIP is 0.01 ml / g, Samples 11 to 14, i.e., the positive electrode active materials in which the Li to Co ratio is greater than or equal to 1.00 and less than or equal to 1.06, exhibit excellent cycling characteristics. In particular, Samples 11 and 12, i.e., the positive electrode active materials in which the Li to Co ratio is greater than or equal to 1.00 and less than or equal to 1.03, exhibit very excellent cycling characteristics. In contrast, in Sample 16, in which the Li to Co ratio is 1.08, the energy density retention rate decreases at a relatively early stage.

[0565] As in Fig. As shown in Figure 47B, in the case where TTIP is 0.02 ml / g, Samples 21 to 24, i.e., the positive electrode active materials in which the Li to Co ratio is greater than or equal to 1.00 and less than or equal to 1.06, exhibit excellent cycling characteristics. Samples 23 and 24, i.e., the positive electrode active materials in which the Li to Co ratio is particularly greater than or equal to 1.05 and less than or equal to 1.06, exhibit extremely excellent cycling characteristics.

[0566] Fig. Figure 48 is a graph showing a comparison between Sample 11 having the best cycle characteristics among Samples 11 to 15 and Sample 23 having the best cycle characteristics among Samples 21 to 25.

[0567] As in Fig. As shown in Figure 48, both Sample 11 and Sample 23 exhibit excellent cycling properties; however, Sample 23, where TTIP is 0.02 ml / g, exhibits better cycling properties. <<Entladekapazitäts-Retentionsrate> >

[0568] Next, Fig. 49 Evaluation results of a discharge capacity retention rate, which is one of the cycle characteristics of each of Samples 21 to 26 and Sample 28.

[0569] The shape of the secondary battery, the materials and the mixing ratio of the positive electrode active material, the conductive additive and the binder in the positive electrode, the counter electrode, the electrolyte solution, the outer part, the cycle property test conditions and the like of Samples 21 to 26 are the same as those in Example 1.

[0570] The secondary battery using Sample 28 was manufactured in a similar manner to the secondary batteries using Samples 21 to 26, except that PVDF was used as a binder and the positive electrode active material (LCO), AB, and PVDF were mixed such that the weight ratio of LCO to AB and PVDF was 95:3:2, and then evaluated.

[0571] As in Fig. As shown in Figure 49, Samples 21 to 24 and Sample 28 exhibit excellent cycling characteristics. In particular, Sample 28 exhibits excellent cycling characteristics. In Sample 28, the discharge capacity retention rate after 50 cycles was greater than or equal to 85%.

[0572] In contrast, in Sample 25 and Sample 26, where the Li to Co ratios are 1.07 and 1.08, respectively, the discharge capacity retention rates decrease at a relatively early time.

[0573] From the above results, it was found that when the TTIP content per weight of the positive electrode active material is 0.02 ml / g, the Li to Co ratio preferably ranges from greater than or equal to 1.00 to less than 1.07. Furthermore, it was found that a sample in which the Li to Co ratio ranges from greater than or equal to 1.05 to less than or equal to 1.06 exhibits very excellent cycling characteristics.

[0574] Fig. 50A to Fig. 50C show charging and discharging curves of the secondary batteries using sample 28, which are shown in Fig. 49 has very excellent cycling properties, Sample 24 and Sample 25, where degradation occurs at a relatively early stage.

[0575] Fig. 50A, Fig. 50B and Fig. Figures 50C show the charge and discharge curves of the secondary batteries using Sample 28, Sample 24, and Sample 25, respectively. Each figure shows an overlap of the results of 50 charge and discharge cycles. As indicated by an arrow in each figure, the charge and discharge capacity decreases from the first cycle to the fiftieth cycle.

[0576] As in Fig. 50A and Fig. As shown in Figure 50B, Sample 28 and Sample 24, which are positive electrode active materials of one embodiment of the present invention, exhibit high charging and discharging capacities and excellent charging and discharging characteristics. Furthermore, it has been found that a decrease in the charging and discharging capacities of each of Sample 28 and Sample 24 in Fig. 50A and Fig. 50B compared to sample 25 in Fig. 50C is significantly suppressed. [Example 4]

[0577] In this example, SEM observation results and SEM-EDX analysis results of the positive electrode active material of Sample 24 formed in Example 2 are described.

[0578] Sample 24 was formed so that Li / Co was 1.06 and TTIP per weight of positive electrode active material was 0.02 ml / g. Fig. Figure 51A shows an SEM image of sample 24. Fig. 51 B and Fig. 51C each show an enlarged image of a part in Fig. 51A.

[0579] As in Fig. 51A to Fig. 51C, there are a large number of protruding regions in a surface portion of the positive electrode active material.

[0580] Show next Fig. 52A-1, Fig. 52A-2, Fig. 52B-1, Fig. 52B-2, Fig. 52C-1 and Fig. 52C-2 Analysis results of the positive electrode active material of Sample 24 using SEM-EDX. Fig. 52A-1 shows an SEM image of a surface portion of the positive electrode active material, Fig. 52A-2 shows a distribution image of titanium, Fig. 52B-1 shows a distribution pattern of magnesium, Fig. 52B-2 shows a distribution pattern of oxygen, Fig. 52C-1 shows a distribution pattern of aluminum and Fig. Figure 52C-2 shows a distribution image of cobalt. It should be noted that in EDX element distribution images in Fig. 52A-2, Fig. 52B-1, Fig. 52B-2, Fig. 52C-1 and Fig. 52C-2 an area where the number of elements is less than or equal to a lower measurement limit is displayed in black, and as the number of elements is increased, the black area becomes white.

[0581] The same areas in Fig. 52A-1, Fig. 52A-2 and Fig. 52B-1 are surrounded by dashed lines. When the areas surrounded by dashed lines were compared, it was found that titanium and magnesium are distributed in the protruding areas in the surface portion of the positive electrode active material.

[0582] Thus, it has been found that the sample 24 is a positive electrode active material including the protruding (protrusion-containing) fourth region 104 containing titanium and magnesium over the third region 103.

[0583] As shown in Example 2, Sample 24 is one of the samples exhibiting very excellent cycling characteristics. Thus, it was found that the positive electrode active material with excellent cycling characteristics can be obtained even when the fourth region is provided in the surface portion or when the fourth region is provided.

[0584] From the above results of Examples 1 to 3, it is clear that when the titanium-containing region is formed in the surface portion, the positive electrode active material with excellent cycling characteristics can be obtained. Furthermore, it has been found that if the ratio of Li to Co is increased to increase the particle diameter of the positive electrode active material, the cycling characteristics might deteriorate; however, the titanium-containing region is formed in the surface portion, thereby expanding the range of the ratio of Li to Co in which excellent cycling characteristics are obtained. Furthermore, it has been found that even when the fourth region containing titanium and magnesium is provided in the surface portion of the positive electrode active material, excellent cycling characteristics are obtained. [Example 5]

[0585] In this example, an example of a method for producing a graphene oxide-coated positive electrode active material is shown, and observation results of the positive electrode active material produced by the method with an electron microscope are described.

[0586] As shown in a process flow diagram in Fig. 53, a process for forming a coating film on a positive electrode active material includes the following steps: weighing graphene oxide (S11); mixing and stirring the graphene oxide and pure water (S12); controlling the pH (S13); adding an active material (S14); completing a suspension (S15); spraying the suspension using a spray-drying device (S16); and collecting particles in a container (S17).

[0587] Note that in (S12), pure water is used as the dispersion medium; however, the dispersion medium is not particularly limited, and ethanol or the like can be used. Additionally, in (S14), the active material is a positive electrode active material.

[0588] Fig. 54 is a schematic view of a spray drying device 280. The spray drying device 280 comprises a chamber 281 and a nozzle 282. A suspension 284 is supplied to the nozzle 282 through a pipe 283. The suspension 284 is supplied to the chamber 281 from the nozzle 282 in the form of mist and dried in the chamber 281. The nozzle 282 can be heated with a heater 285. In this case, an area of ​​the chamber 281 that is close to the nozzle 282, for example an area that is surrounded by the double-dashed line in Fig. 54 is also heated by the heater 285.

[0589] In the case of using a suspension containing a positive electrode active material and graphene oxide as the suspension 284, a powder of the positive electrode active material coated with the graphene oxide is collected in a collecting container 286 through the chamber 281.

[0590] The air in the chamber 281 can be sucked in by an aspirator or the like through a path indicated by an arrow 288.

[0591] An example of the conditions for forming the coating film is shown below.

[0592] First, a suspension was formed by dispersing graphene oxide in a solvent.

[0593] Although graphene oxide is highly dispersible in pure water, pure water can react with a subsequently added active material, potentially dissolving Li or damaging an active material, thereby altering the surface structure. Thus, the graphene oxide was dispersed in a solution with a ratio of ethanol to pure water of 4:6.

[0594] Stirring to disperse the graphene oxide in a solution was performed under the following conditions: a stirrer and an ultrasonic wave generator were used; a rotation rate was 750 rpm; and the ultrasonic wave irradiation time was 2 minutes.

[0595] Then, an aqueous LiOH solution was added dropwise to adjust the pH to pH 7 (25 °C).

[0596] The positive electrode active materials (in this example, lithium cobalt oxide particles manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. (product name: C-20F)) were added, and stirring was performed using a stirrer and an ultrasonic wave generator under the following conditions: a rotation rate of 750 rpm; and an ultrasonic wave irradiation time of 1 minute. The suspension was prepared by the above method. The above lithium cobalt oxide particles manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. (product name: C-20F) contain at least fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus, and each has a diameter of approximately 20 μm.

[0597] Next, the suspension was uniformly sprayed with a spray nozzle (with a nozzle diameter of 20 µm) of the spray dryer to obtain a powder. The hot air temperature of the spray dryer was 160 °C, the outlet temperature was 40 °C, and the N2 gas flow rate was 10 l / min.

[0598] Fig. Figure 55 shows a cross-sectional TEM image of the obtained powder. Fig. Figure 56 shows an SEM image of the obtained powder. When a positive electrode active material that was the same as the sprayed positive electrode active material (C-20F, manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.) was mixed with graphene oxide as a comparison example using a planetary centrifugal mixer, the coating was insufficient. Fig. Figure 57 shows an SEM image of the comparison example.

[0599] It has been found that the coating film is evenly distributed on the surface of the powder in comparison to 57 Fig. 56 is trained.

[0600] Fig. 58A and Fig. 58B illustrates a cross-sectional structure example of an active material layer 200 coated with graphene oxide using a spray-drying device and containing a graphene compound as a conductive additive.

[0601] Fig. 58A is a longitudinal sectional view of the active material layer 200. The active material layer 200 includes positive electrode active material particles 100 coated with graphene oxide, a graphene compound 201 as a conductive additive, and a binder (not shown). As the graphene compound 201, for example, graphene or multilayer graphene can be used here. The graphene compound 201 preferably has a sheet-like shape. The graphene compound 201 may have a film-like shape formed from multiple layers of multilayer graphene and / or multiple layers of graphene that partially overlap.

[0602] In the longitudinal section of the active material layer 200, as shown in Fig. 58B, the positive electrode active material 100 coated with a coating film 105 formed of graphene oxide is in contact with the graphene compound 201. A plurality of graphene compounds 201 are formed to partially contact the positive electrode active material 100 coated with the coating film 105 and adhere to the coating film 105 of the adjacent positive electrode active material 100, so that the graphene compounds 201 are in contact with each of the positive electrode active materials 100.

[0603] The graphene compound 201 and the coating film 105 are formed using carbon-based materials; thus, an excellent conductive path can be formed.

[0604] The coating film 105 is effective in protecting the crystal structure of the positive electrode active material 100 from coming into contact with the electrolyte solution and in forming the excellent conduction path. Reference symbol

[0605] 11a: Positive electrode, 11b: Negative electrode, 12a: Lead, 12b: Lead, 14: Separator, 15a: Connecting portion, 15b: Connecting portion, 17: Fastener, 50: Secondary battery, 51: Outer part, 61: Bending portion, 62: Sealing portion, 63: Sealing portion, 71: Crest line, 72: Valley line, 73: Space, 100: Positive electrode active material, 101: First region, 101p: Crystal plane, 102: Second region, 102p: Crystal plane, 103: Third region, 103p: Crystal plane, 104: Fourth region, 105: Coating film, 106: Crack portion, 110: Particle, 111: Region, 112: Titanium-containing layer, 114: Cobalt oxide layer, 120: Particle, 121: Region, 122: Titanium-containing layer, 124: Cobalt oxide layer, 125: Lithium titanate-containing layer, 200: Active material layer, 201: Graphene compound, 214: Separator, 280: Spray-drying device, 281: Chamber, 282: Nozzle, 283: Tube, 284: Suspension, 285: Heater, 286: Collecting container, 288: Arrow, 300: Button cell secondary battery,301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 500: laminated secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolyte solution, 509: outer part, 510: positive electrode terminal electrode, 511: negative electrode terminal electrode, 600: cylindrical Secondary battery, 601: Positive electrode cap, 602: Battery can, 603: Positive electrode terminal, 604: Positive electrode, 605: Separator, 606: Negative electrode, 607: Negative electrode terminal, 608: Insulating plate, 609: Insulating plate, 611: PTC element, 612: Safety valve mechanism,613: conductive plate, 614: conductive plate, 615: module, 616: line, 617: temperature control device, 900: printed circuit board, 910: label, 911: terminal, 912: circuit, 913: secondary battery, 914: antenna, 915: antenna, 916: layer, 917: layer, 918: antenna, 920: display device, 921: sensor, 922: terminal, 930: case, 930a: case, 930b: case, 931: negative electrode, 932: positive electrode, 933: separator, 950: wound part, 951: terminal, 952: terminal, 980: laminated secondary battery, 981: film, 982: film, 993: wound part, 994: negative electrode, 995: positive electrode, 996: separator, 997: terminal electrode, 998: terminal electrode, 7100: portable display device, 7101: casing, 7102: display section, 7103: operation button, 7104: secondary battery, 7200: portable information terminal, 7201: casing, 7202: display section, 7203: band, 7204: buckle, 7205: operation button, 7206: input / output terminal, 7207: icon, 7300: display device,7304: Display section, 7400: Mobile phone, 7401: Housing, 7402: Display section, 7403: Operation button, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Secondary battery, 7408: Terminal electrode, 7409: Current collector, 7500: Vaporizer, 7501: Atomizer, 7502: Cassette, 7504: Secondary battery, 8000: Display device, 8001: Housing, 8002: Display section, 8003: Speaker section, 8004: Secondary battery, 8021: Ground-based charger, 8022: Cable, 8024: Secondary battery, 8100: Lighting device, 8101: Housing, 8102: Light source, 8103: Secondary battery, 8104: Ceiling, 8105: Wall, 8106: Floor, 8107: Window, 8200: Indoor unit, 8201: Casing, 8202: Air outlet, 8203: Secondary battery, 8204: Outdoor unit, 8300: Electric freezer-refrigerator, 8301: Casing, 8302: Refrigerator door, 8303: Freezer door, 8304: Secondary battery, 8400: Vehicle, 8401: Headlight, 8406: Electric motor, 8500: Vehicle, 8600: Scooter, 8601: Side mirror,8602: Secondary battery, 8603: Turn signal, 8604: Under-seat storage unit, 9600: Tablet computer, 9625: Power-saving mode switch, 9626: Display mode switch, 9627: Power switch, 9628: Operation switch, 9629: Bracket, 9630: Case, 9630a: Case, 9630b: Case, 9631: Display section, 9631a: Display section, 9631b: Display section, 9633: Solar cell, 9634: Charge / discharge control circuit, 9635: Energy storage unit, 9636: DC-DC converter, 9637: Converter, 9640: Movable part.

[0606] This application is based on Japanese Patent Application Serial No. 2016-133997 filed with the Japan Patent Office on July 6, 2016, Japanese Patent Application Serial No. 2016-133143 filed with the Japan Patent Office on July 5, 2016, Japanese Patent Application Serial No. 2017-002831 filed with the Japan Patent Office on January 11, 2017, Japanese Patent Application Serial No. 2017-030693 filed with the Japan Patent Office on February 22, 2017, Japanese Patent Application Serial No. 2017-084321 filed with the Japan Patent Office on April 21, 2017, and Japanese Patent Application Serial No. 2017-084322 filed with the Japan Patent Office on April 21, 2017. 2017-119272, filed with the Japan Patent Office on June 19, 2017, the entire contents of which are hereby incorporated by reference into this disclosure. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2012-018914

[0006] JP 2015-201432

[0006] JP 2016-133143

[0606] JP 2017-030693

[0606] < / negativelektrodenstromkollektor> < / negativelektrodenaktivmaterial> < / positivelektrodenstromkollektor> < / positivelektrodenaktivmaterialschicht>

Claims

[1] Lithium-ion secondary battery, comprising: a positive electrode comprising a positive electrode active material particle and a coating film covering the positive electrode active material particle, wherein the positive electrode active material particle comprises magnesium, titanium, fluorine and lithium cobaltate, wherein the positive electrode active material particle has a region comprising a rock salt crystal structure, wherein the coating film is in contact with the region comprising the rock salt crystal structure, wherein the region comprising the rock salt crystal structure comprises cobalt, magnesium oxide, titanium and fluorine, wherein in a part of the magnesium oxide contained in the region comprising the rock salt crystal structure, fluorine is bonded to magnesium as a substitute for oxygen, and wherein the region comprising the rock salt crystal structure comprises a solid solution comprising cobalt oxide and magnesium oxide. [2] Lithium-ion secondary battery, comprising: a positive electrode comprising a positive electrode active material particle and a coating film covering the positive electrode active material particle, wherein the positive electrode active material particle comprises magnesium, titanium, fluorine and lithium cobaltate, wherein the positive electrode active material particle has a region comprising a rock salt crystal structure, wherein the coating film is in contact with the region comprising the rock salt crystal structure, wherein the region comprising the rock salt crystal structure comprises cobalt, magnesium oxide, titanium and fluorine, wherein in the region comprising the rock salt crystal structure, part of magnesium is bonded to oxygen and fluorine, and wherein the region comprising the rock salt crystal structure comprises a solid solution comprising cobalt oxide and magnesium oxide. [3] Lithium-ion secondary battery, comprising: a positive electrode comprising a positive electrode active material particle and a coating film covering the positive electrode active material particle, wherein the positive electrode active material particle comprises magnesium, titanium, fluorine and lithium cobaltate, wherein the positive electrode active material particle has a region comprising a rock salt crystal structure, wherein the coating film is in contact with the region comprising the rock salt crystal structure, wherein the region comprising the rock salt crystal structure comprises magnesium oxide, titanium and fluorine, and wherein a peak position of a binding energy of fluorine is higher than or equal to 682 eV and lower than or equal to 685 eV when the positive electrode active material particle is measured by X-ray photoelectron spectroscopy. [4] The lithium ion secondary battery according to claim 3, wherein a measurement range of X-ray photoelectron spectroscopy is a range of up to 5 nm in a depth direction. [5] Lithium ion secondary battery according to claim 3 or 4, wherein the region comprising the rock salt crystal structure further comprises cobalt, and wherein the region comprising the rock salt crystal structure comprises a solid solution comprising cobalt oxide and magnesium oxide. [6] The lithium ion secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material particle has a surface in contact with the coating film comprising cobalt and oxygen. [7] The lithium ion secondary battery according to any one of claims 1 to 6, wherein the coating film is a coating film comprising carbon or a film comprising lithium or a decomposition product of an electrolytic solution. [8] Lithium ion secondary battery according to one of claims 1 to 7, wherein the positive electrode active material particle comprises a layered rock salt crystal structure, wherein the layered rock salt crystal structure is located further inside than the region comprising the rock salt crystal structure, and wherein a region connecting the layered rock salt crystal structure and the rock salt crystal structure comprises an element selected from the group consisting of titanium, vanadium, manganese, iron, chromium, niobium, cobalt, zinc, zirconium and nickel. [9] Lithium ion secondary battery according to one of claims 1 to 8, wherein the positive electrode active material particle comprises a layered rock salt crystal structure, wherein the layered rock salt crystal structure is located further inside than the region comprising the rock salt crystal structure, and wherein the positive electrode active material particle comprises nickel present between the layered rock salt crystal structure and the rock salt crystal structure. [10] Lithium ion secondary battery according to one of claims 1 to 9, wherein the positive electrode active material particle comprises a layered rock salt crystal structure, wherein the layered rock salt crystal structure is located further inside than the region comprising the rock salt crystal structure, and wherein the positive electrode active material particle comprises a spinel crystal structure existing between the layered rock salt crystal structure and the rock salt crystal structure. [11] The lithium ion secondary battery according to any one of claims 1 to 10, wherein the positive electrode active material particle comprises a crack portion comprising magnesium.

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