Method for manufacturing a lithium-ion secondary battery

Abstract

Method for manufacturing a lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises a positive electrode, a negative electrode and an electrolyte solution, wherein the positive electrode contains a positive electrode active material, wherein the positive electrode active material comprises a positive electrode active material particle, and wherein the method comprises the following steps: Coating a composite oxide with a titanium-containing material, wherein the composite oxide contains lithium, cobalt, magnesium, and fluorine; and Heating the composite oxide at a temperature of 500 °C or higher and 1200 °C or lower, wherein the heating step segregates titanium, magnesium and fluorine in a crack section of the positive electrode active material particle, wherein magnesium and fluorine are segregated in a surface section of the positive electrode active material particle, and wherein titanium diffuses into the interior of the positive electrode active material particle.

Description

Technical field

[0001] The present invention relates to a method for producing a lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises a positive electrode, a negative electrode and an electrolyte solution, wherein the positive electrode contains a positive electrode active material, wherein the positive electrode active material comprises a positive electrode active material particle.

[0002] The term "energy storage device" in this description 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 called a secondary battery), a lithium-ion capacitor, and an electrical double-layer capacitor.

[0003] It should be noted that in this description, electrical equipment refers to all equipment that includes energy storage devices, and that electro-optical equipment that includes energy storage devices, information terminal equipment that includes energy storage devices, and the like are all electrical equipment. 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 for portable information devices, such as mobile phones, smartphones, tablets and laptops, portable music players, digital cameras, medical devices, next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs), has increased significantly. Lithium-ion secondary batteries are essential as 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). A method for manufacturing a lithium-ion secondary battery is also known from the document "Shim et al., Synergistic effects of coating and doping for lithium ion battery cathode materials: synthesis and characterization of lithium titanate-coated LiCoO2 with Mg doping, Electrochimica Acta 186 (2015) 201-208". [Reference][Patent documents] [Patent Document 1] Japanese Patent Publication JP 2012-018914A [Patent document 2] Japanese patent disclosure JP 2015-201432A Disclosure of the invention

[0007] The development of lithium-ion secondary batteries and the positive electrode active materials used in them can be improved with regard to charging and discharging characteristics, cycle characteristics, reliability, safety, cost, and the like.

[0008] One object of an 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 an embodiment of the present invention is to provide a secondary battery with high capacity. Another object of an embodiment of the present invention is to provide a secondary battery with excellent charge and discharge characteristics. Another object of an 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 new material, a novel active material particle, a novel secondary battery or a training method for it.

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

[0011] At least one of the aforementioned problems is solved by a method according to claim 1. Advantageous embodiments are specified in the dependent claims. In one embodiment of the present invention, two types of regions, which differ from a region within the positive electrode active material, are provided in a surface section of the positive electrode active material. It is preferred 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 area contains titanium and the outer area contains magnesium. In addition, these two types of areas can overlap.

[0013] Furthermore, it is preferred that the inner area is formed by a coating process, such as a sol-gel process, and the outer area 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 located within the positive electrode active material. The second and third regions are located in a surface portion of the positive electrode active material. The third region is located 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 comprising an oxide of a second transition metal, and the non-stoichiometric compound has a rock salt crystal structure.The third area contains a combination of representative elements, and the combination of representative elements exhibits 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 and third regions may each contain cobalt.

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

[0018] In the above structure, the 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 the 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 section 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 invention 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 more and 20 hours or less 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 to heat the collected precipitation 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 less.

[0021] In the above training method, the 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 formation 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 formation process, 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 training method, lithium carbonate, cobalt oxide, magnesium oxide and lithium fluoride can be used as the 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. The coating film used to cover the surface of the positive electrode active material can be a carbon-containing coating film (a film containing a graphene compound) or a coating film containing lithium or a decomposition product of an electrolyte solution.

[0026] In particular, a powder is preferably obtained 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 manufacturing device in which a spray drying process is used in which a dispersion medium is removed from a suspension by introducing a hot air stream.

[0027] Repeated charging and discharging cycles can lead to deformation of the positive electrode active material particles, such as cracking or damage. Such deformation is said to expose a new surface of the positive electrode active material, which then comes into contact with an electrolyte solution, causing a decomposition reaction or similar process that degrades the cycle life and charging / 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, if 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, which has a large weight per unit volume with graphene oxide, whose weight is relatively small, the coating is insufficient.

[0030] To coat the surfaces of the positive electrode active material particles with graphene oxide, a method is preferably used in which the graphene oxide and a polar solvent (such as water) are mixed, an ultrasonic treatment is performed, the positive electrode active material particles are mixed in to produce the suspension, and a dried powder is produced using a spray-drying device. The dried powder produced in this way is sometimes referred to as a composite material.

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

[0032] If the particle diameter is smaller than the nozzle diameter, there will be a multitude of particles in a single droplet of the spray liquid ejected from the nozzle. When the particle surface is observed after drying under the condition where the largest particle size is smaller than the nozzle diameter, some areas are found to be coated with graphene oxide; however, the coating is insufficient.

[0033] The nozzle diameter of the spray drying device is preferably essentially equal to the largest particle size of the active material, as this improves the coverage capacity of the active material. Furthermore, the largest particle size of the positive electrode active material is preferably adjusted such that it is essentially equal to the nozzle diameter during the formation of 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 using a spray drying device, resulting in 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 when the amount of graphene oxide is increased. This could etch part of the surface of the positive electrode active material (e.g., LiCoO2 containing Mg and F). Therefore, the pH of the suspension is preferably adjusted before spraying to approximately pH 7, i.e., nearly neutral, or pH 8 or higher, i.e., alkaline. An aqueous LiOH solution is preferably used for pH adjustment. For example, if LiCoO2 is used for the positive electrode active material and only pure water is used as the dispersion medium for the suspension, the surface of the positive electrode active material may be damaged. Therefore, a mixed solution of ethanol and water is used as the dispersion medium for the suspension, which reduces the risk of damage to the surface of the active material.

[0036] The suspension is formed in the manner described above, enabling the efficient production of the positive electrode active material, whose surface is coated with graphene oxide. Coating the surface with graphene oxide prevents deformation of the positive electrode active material particles, such as cracking or damage. Furthermore, even after the positive electrode active material, coated with graphene oxide, is exposed to air following its formation, changes in its properties or deterioration are suppressed. Here, "after formation" refers to the period from the completion of the positive electrode active material's formation until the commencement of the production of the secondary battery containing the positive electrode active material, and includes storage, transport, and similar processes.Furthermore, when the coating film forms, it prevents the positive electrode active material and the electrolyte solution from coming into direct contact with each other and reacting; thus, the secondary battery using the coating film has a high reliability.

[0037] A known apparatus can be used for the spray drying process; 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. Reduced graphene oxide is sometimes referred to as "RGO." In RGO, some of the oxygen atoms remain in a state of oxygen or a group of atoms containing oxygen bonded to carbon. For example, RGO may include 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 positive electrode active material described above or the positive electrode active material described above coated with a coating film, and a negative electrode.

[0040] The secondary battery can have a variety of shapes to fit the shape of the device to be used, for example 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 a reduction in capacity 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. Finally, a novel material, a novel active material particle, a novel secondary battery, or a training method for these is provided. Brief description of the drawings

[0042] In the accompanying drawings: Fig. Figures 1A to 1C show examples of a positive electrode active material; Fig. 2A and Fig. Figure 2B represents crystal structures of a positive electrode active material; Fig. Figure 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 demonstrates a sol-gel process; Fig. 5A to 5C represent a segregation model of elements contained in a positive electrode active material; Fig. 6A to 6D represent a segregation model of elements contained in a positive electrode active material; Fig. 7A and Fig. Figure 7B shows cross-sectional views of an active material layer containing a graphene compound as a conductive additive; Fig. 8A to 8C represent a method for charging a secondary battery; Fig. 9A to 9D describe a method for charging a secondary battery; Fig. 10 presents a method for discharging a secondary battery; Fig. 11A to 11C represent a button cell secondary battery; Fig. 12A to 12D represent a cylindrical secondary battery; Fig. 13A and Fig. 13B represents 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 provides examples of secondary batteries; Fig. 16 represents an example of a secondary battery; Fig. 17A to 17C represent a laminated secondary battery; Fig. 18A and Fig. 18B represents a laminated secondary battery; Fig. 19 is an exterior view of a secondary battery; Fig. 20 is an external view of a secondary battery; Fig. 21A to 21C represent a training procedure for a secondary battery; Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D represents a flexible secondary battery; Fig. 23A and Fig. 23B represents a flexible secondary battery; Fig. 24A to 24H represent examples of electrical devices; Fig. 25A to 25C represent an example of an electrical device; Fig. 26 presents examples of electrical appliances; Fig. 27A to 27C provide examples of electrical appliances; Fig. Figure 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 images of a positive electrode active material of a comparison example of example 1; Fig. Figure 32 is a graph showing TEM-EDX line analysis results of a positive electrode active material of Example 1; Fig. Figure 33 is a graph showing the charging and discharging characteristics of a secondary battery of example 1; Fig. Figure 34 is a graph showing the charging and discharging characteristics of a secondary battery of a comparison example of Example 1; Fig. Figure 35 is a graph showing the cycle characteristics of a secondary battery of example 1; Fig. Figure 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 layer analysis images of a comparison example 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 layer 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 layer analysis images of a comparison example 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 layer analysis images of a positive electrode active material of example 2; Fig. 41A and Fig. Figures 41B are each a graph showing EDX point analysis results of Example 2; Fig. 42A and Fig. Figures 42B are each a graph showing EDX point analysis results of Example 2; Fig. Figure 43 is a graph showing the rate characteristics of a secondary battery of Example 2; Fig. Figure 44 is a graph showing the temperature properties of a secondary battery of Example 2; Fig. Figure 45 is a graph showing the cycle characteristics of a secondary battery of example 2; Fig. 46A and Fig. Figures 46B each represent a graph showing XPS analysis results of a positive electrode active material of Example 3; Fig. 47A and Fig. Figures 47B each represent a graph showing the cycle characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. Figure 48 is a graph showing the cycle characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. Figure 49 is a graph showing the cycle characteristics of a secondary battery containing a positive electrode active material of Example 3; Fig. 50A to 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 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 represents a spray drying device of Example 5; Fig. Figure 55 is a TEM image showing an embodiment of the present invention of Example 5; Fig. Figure 56 is a SEM image showing an embodiment of the present invention of Example 5; Fig. Figure 57 is a SEM image showing a comparison example of Example 5; and Fig. 58A and Fig. Figure 58B shows cross-sectional views of an active material layer of Example 5, which contains a graphene compound as a conductive additive. Best way to implement the invention

[0043] Embodiments of the present invention are described in detail below with reference to the drawings. It should be noted that the present invention is not limited to the following description, and it will be readily understood by a person 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 considered as limited to the description in the following embodiments.

[0044] It should be noted that in the drawings used in this description, the sizes, thicknesses, and other dimensions of components such as a positive electrode, a negative electrode, an active material layer, a separator, and an outer part are, in some cases, exaggerated for the sake of simplicity. Therefore, the dimensions of the components are neither limited to the sizes shown in the drawings nor to the size ratios between the components.

[0045] It should be noted that in structures of the present invention described in this description and the like, identical sections or sections with similar functions are provided with common reference numerals in different drawings, and the descriptions of these are not repeated. Furthermore, the same hatching pattern is used for sections with similar functions, and in some cases, the sections are not specifically provided with reference numerals.

[0046] In this description and similar texts, the Miller index is used to indicate crystal planes and orientations. In crystallography, an overline is placed over a number in a specification that uses the Miller index; however, in this description and similar texts, due to limitations in the number of specifications, crystal planes and orientations are expressed by placing a minus sign (-) before a number instead of placing the overline over a number. Furthermore, a single direction indicating an orientation in the crystal is represented by "[ ]", a set direction indicating all equivalent orientations is represented by "< >", a single direction indicating a crystal plane is represented by "( )", and a set plane exhibiting equivalent symmetry is represented by "{}".In the drawings, the crystal planes and orientations are expressed by a number with an overline, which is an original crystallographic notation. It should be noted that 1 Å equals 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 description and similar texts, 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 arrangement with alternating cations and anions is present, and the lithium and transition metal are regularly arranged to form a two-dimensional plane, allowing lithium to diffuse two-dimensionally. It should be noted that a defect, such as a cation or anion vacancy, may exist. Strictly speaking, in the layered rock salt crystal structure, the lattice of a rock salt crystal is distorted in some cases.

[0049] In this description and similar texts, a rock salt crystal structure refers to a structure in which cations and anions are arranged alternately. It should be noted that a cation or anion defect 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, there is a crystal plane in which the directions of the cubic close-packed structures composed of anions are aligned. A space group of the layered rock salt crystal is R-3m, which differs from a space group Fm-3m of a general rock salt crystal and a 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 differs from that in the rock salt crystal.In this description, in the layered rock salt crystal and the rock salt crystal, a state in which the directions of the cubic most densely packed structures consisting of anions are aligned with each other is referred to as a state in which crystal orientations are essentially aligned with each other.

[0051] Whether the crystal orientations in two regions are aligned or not can be assessed using a transmission electron microscope (TEM) image, a scanning transmission electron microscope (STEM) image, a high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image, annular bright field scanning transmission electron microscopy (ABF-STEM) image, and similar techniques. X-ray diffraction, electron diffraction, neutron diffraction, and similar methods can also be used for evaluation. In the TEM image and similar images, the alignment of cations and anions can be observed as a repetition of bright 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, a state is observed in which the angle between the repetition of light and dark lines in the layered rock salt crystal and the repetition of light and dark lines in the rock salt crystal is less than or equal to 5°, preferably less than or equal to 2.5°. It should be noted 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 metallic elements.

[0052] Furthermore, in this description and similar texts, a state in which two-dimensional interface structures exhibit similarity is referred to as "epitaxy." Crystal growth in which two-dimensional interface structures exhibit similarity is referred to as "epitaxial growth." Additionally, a state in which three-dimensional structures exhibit similarity, or orientations are crystallographically similar, is referred to as "topotaxy." In the case of topotaxy, therefore, when a portion 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 essentially aligned with one another. (Design 1) [Structure of the positive electrode active material]

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

[0054] As in Fig. As shown in Figure 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 area 102 and the third area 103 can each differ depending on their positions.

[0056] Furthermore, the third region 103 can be located within the positive electrode active material 100. For example, if the first region 101 is a polycrystal, the third region 103 can be located near a grain boundary. Additionally, the third region 103 can be located in a section that has crystal defects or a crack in or near the positive electrode active material 100. Fig. 1B shows portions of grain boundaries indicated by dotted lines. In this description and the like, crystal defects refer to defects that can be observed in a TEM image and the like, i.e., a structure in which another element enters a crystal, a cavity, and the like. Furthermore, a crack segment, for example, refers to a crack or fracture point that, like crack segment 106, is located in Fig. 1C is represented as being formed in a particle.

[0057] Similarly, as in Fig. As shown in Figure 1B, the second region 102 may be present within the positive electrode active material 100. For example, if the first region 101 is a polycrystal, the second region 102 may be located near a grain boundary. Furthermore, the second region 102 may be located in a section that has crystal defects or a crack in or near the positive electrode active material 100. In addition, the third region 103 and the second region 102 may overlap within the positive electrode active material 100. <Erster Bereich 101 >

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

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

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

[0061] This means that the first region may contain lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which some 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 contributes in particular to a charging and discharging reaction in the positive electrode active material 100. In order 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 with a layered rock salt crystal structure exhibits characteristics such as a high discharge capacity and low resistance due to lithium, which can diffuse two-dimensionally, and is preferably used for the first region 101. Additionally, in the case where the first region 101 has a layered rock salt crystal structure, a 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 could 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 sometimes be observed using TEM or similar instruments. Additionally, the average crystal grain size can be calculated from the XRD full width at half maximum (FWHM) measurement.

[0065] The polycrystal exhibits a clear crystal structure; thus, a two-dimensional diffusion path for lithium ions can be adequately ensured. Additionally, a polycrystal is easier to produce compared to a single crystal; therefore, a polycrystal is preferably used for the first area 101.

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

[0067] The second area, 102, contains an oxide of a second transition metal. In other words, the second area, 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 differs from the first transition metal.

[0069] In this description and similar usage, a non-stoichiometric metal refers to a metal that can have a variety of valences. A non-stoichiometric compound also refers to a compound of a metal that can have a variety of valences and another element.

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

[0071] The second region 102 serves as a buffer region connecting the first region 101 with the third region 103, which will be described later. In the non-stoichiometric compound, an atomic distance can be altered in accordance with a valence change of a metal contained within the non-stoichiometric compound. Additionally, a cation or anion vacancy and dislocation (also known as a Magneli phase) are frequently formed in the non-stoichiometric compound. Thus, the second region 102, acting as a buffer region, can absorb a strain generated between the first region 101 and the third region 103.

[0072] Furthermore, the second region 102 can contain lithium in addition to the second transition metal and oxygen. For example, it can contain lithium titanate or lithium manganite. Moreover, the second region 102 can contain a representative element that is 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 preferred because the second region 102 serves as a buffer region.

[0073] This means that the second area may contain 102 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 can contain the first transition metal. For example, the second transition metal can be present in part of a first transition metal site of the composite oxide that includes the first transition metal.

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

[0076] Furthermore, the second area may contain 102 fluorine.

[0077] The second region 102 preferably has a crystal structure that is the same as that of the third region 103, which is described later. In this case, the orientations of crystals of 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 can exhibit strain as long as a structure in which six oxygen atoms are adjacent to cations is maintained. Additionally, a cation defect may be present in part of the second region 102.

[0080] Furthermore, part of the second area 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 capacitance could decrease. Therefore, the second region 102 is preferably located in a depth direction extending from the surface of the positive electrode active material 100 to a depth of 20 nm, preferably 10 nm. The second transition metal may exhibit a concentration gradient. <Dritter Bereich 103>

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

[0083] The third region 103 is in contact with an electrolyte solution when the positive electrode active material 100 is used in a secondary battery. Therefore, a material is preferably used for the third region 103 that undergoes minimal electrochemical changes during charging and discharging and is not readily transformed by contact with the electrolyte solution. A stoichiometric compound of representative elements that is electrochemically stable is preferably used for the third region 103. The positive electrode active material 100 encompasses the third region 103 in a surface section to improve the 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 the capacity change of the secondary battery is small even when charging and discharging is 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, thereby improving the diffusion properties of lithium. This makes it less likely that the third region, 103, will impede charging and discharging. Furthermore, the presence of fluorine in a surface section of a positive electrode active material particle can, in some cases, increase corrosion resistance to hydrofluoric acid produced by the decomposition of an electrolyte solution.

[0086] Furthermore, the third area can include 103 lithium, the first transition metal and the second transition metal.

[0087] The compound of representative elements contained in the third region 103 preferably exhibits a rock salt crystal structure. If the third region 103 exhibits a rock salt crystal structure, the orientations of the crystals are likely to be aligned with those of the second region 102. The orientations of crystals in 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 function as a more stable coating layer.

[0088] However, the entire third region 103 does not necessarily exhibit a rock salt crystal structure. For example, the third region 103 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.

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

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

[0091] If the thickness of the third region 103 is too small, its function in increasing stability during charging and discharging is impaired; however, if the thickness of the third region 103 is too large, the capacity could 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 contains fluorine, the fluorine is preferably present in a different binding state than magnesium fluoride (MgF₂), lithium fluoride (LiF), and cobalt fluoride (CoF₂). In particular, when an XPS analysis is performed near the surface of the positive electrode active material 100, the binding energy peak position 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 binding energy does not correspond to those of MgF₂, LiF, and CoF₂.

[0093] In this description 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, releasing oxygen and causing the crystal structure to become unstable, thus degrading the positive electrode active material. However, the positive electrode active material 100 of an embodiment of the present invention comprises a second region 102, which serves as a buffer region, and a third region 103, which is 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 also occur 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, is carried out, 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 topotax (is topotactic) exhibiting crystal orientations that are essentially three-dimensionally aligned with those of a base region. Thus, the first region 101, the second region 102, and the third region 103 can all become a topotax (be topotactic).

[0096] If 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 that exhibits a stable bond with the first region. As a result, the positive electrode active material 100, which has 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, changes 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 as a result of charging, the coating layer with its 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 unconformity between crystals in a base region and crystals where crystal growth is induced is important.

[0099] In this description and the like, the degree of unconformity 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 the 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 induce heteroepitaxial growth, the degree of unconformity f between crystals in a basal region and crystals where growth is induced must be less than or equal to 0.12. To induce more stable heteroepitaxial growth to form a layered structure, the degree of unconformity f is preferably less than or equal to 0.08, and 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 unconformity 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 unconformity 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 conditions described above are shown below: The degree of unconformity 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 unconformity 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] First show Fig. 2A and Fig. 2B as well as Fig. 3 an example in which the first transition metal is cobalt, the first area contains 101 lithium cobaltate with a layered rock salt crystal structure, the second transition metal is titanium, the second area contains 102 lithium titanate with a rock salt crystal structure, and the compound of representative elements in the third area is 103 magnesium oxide with a rock salt crystal structure.

[0105] Fig. 2A presents 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. 2A presents models, each viewed from the b-axis direction.

[0106] Out of Fig. 2A does not show that the layered rock salt crystals and the rock salt crystals lead to a topotaxy. Here, the layered rock salt crystals are being viewed from a different direction (e.g., a direction indicated by an arrow pointing inwards). Fig. 2A is shown). Fig. 2B presents 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 can be considered.

[0107] As in Fig. As shown in Figure 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 shown from the <100> -plane direction. Additionally, the nearest neighbor distances between a metal and oxygen exhibit 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 then describes the degree of unconformity 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.

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

[0110] Additionally, the distance between metals via oxygen in a {100} crystal plane 103p {100} of magnesium oxide with the rock salt crystal structure in the third region 103 is 4.21 Å. Thus, the degree of unconformity f between the crystal plane 102p {100} and the crystal plane 103p {100} is 0.02.

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

[0112] Although in Fig. Not shown in Figure 3, the degree of unconformity f is 0.05 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. This means that, due to the second region 102, the degree of unconformity can be small. Furthermore, 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 exhibit a more stable topotaxy (topotactic stability). Thus, the second region 102 and the third region 103 can act as a coating layer that exhibits 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 situations where crystal planes which may 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 area contains 101 lithium cobaltate with a layered rock salt crystal structure, the second transition metal is manganese, the second area contains 102 manganese oxide with a rock salt crystal structure, and the compound of representative elements in the third area is 103 calcium oxide with a rock salt crystal structure.

[0115] In this case too, as in Fig. 2A and Fig. 2B as well as Fig. 3 shown, then, 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 that of the rock salt crystals in the second region 102 and the third region 103, which are shown by the <100> -plane direction can be considered.

[0116] The degree of unconformity 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. A distance between metals over oxygen in a crystal plane (1-1-4) of lithium cobaltate with the layered rock salt crystal structure in the first region 101 is 4.01 Å. Furthermore, a distance between metals over oxygen in a crystal plane {100} of manganese oxide with the rock salt crystal structure in the second region 102 is 4.45 Å. Thus, the degree of unconformity 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] Additionally, the distance between metals via oxygen in a crystal plane {100} of calcium oxide with the rock salt crystal structure in the third region 103 is 4.82 Å. Thus, the degree of unconformity 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 area 101 and the second area 102 and the degree of discordance between the second area 102 and the third area 103 are sufficiently small; thus, the first area 101, the second area 102 and the third area 103 can be a topotaxy.

[0119] The degree of unconformity 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, is 0.20; thus, it is difficult to induce heteroepitaxial growth. That is, due to the second region 102, heteroepitaxial growth from the first region to the third region can be induced. Therefore, the second region 102 and the third region 103 can act as a coating layer that exhibits 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 area is 101 lithium nickel manganese cobalt oxide (LiNi). 0,33 Co 0,33 Mn 0,33O2) with a layered rock salt crystal structure, the second transition metal is manganese, the second area contains 102 manganese oxide with a rock salt crystal structure, and the compound of representative elements in the third area is 103 calcium oxide with a rock salt crystal structure.

[0121] In this case too, as in Fig. 2A and Fig. 2B as well as Fig. As shown in Figure 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 shown from the <100> -plane direction is considered. The degree of unconformity 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] The distance between metals over oxygen in a crystal plane (1-1-4) of lithium nickel manganese cobalt oxide with the layered rock salt crystal structure in the first region 101 is 4.07 Å. Furthermore, the distance between metals over oxygen in a crystal plane {100} of manganese oxide with the rock salt crystal structure in the second region 102 is 4.45 Å. Thus, the degree of unconformity 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] Additionally, the distance between metals via oxygen in a crystal plane {100} of calcium oxide with the rock salt crystal structure in the third region 103 is 4.82 Å. Thus, the degree of unconformity 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 area 101 and the second area 102 and the degree of discordance between the second area 102 and the third area 103 are sufficiently small; thus, the first area 101, the second area 102 and the third area 103 can be a topotaxy.

[0125] The degree of unconformity 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 is 0.18; thus, it is difficult to induce heteroepitaxial growth. That is, by providing the second region 102, heteroepitaxial growth from the first region to the third region can be induced. Thus, the second region 102 and the third region 103 can serve as a coating layer that exhibits 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 exhibits a concentration gradient in some cases. For example, the second transition metal may exhibit a concentration gradient in the second region 102. Additionally, the third region 103 may exhibit a concentration gradient of a representative element, since a representative element is preferably segregated in the third region 103, as will be described later. Therefore, the boundaries between the regions are not always clear.

[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, fast Fourier transform (FFT) analysis, energy dispersive X-ray spectrometry (EDX), depth analysis by time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, thermal desorption spectroscopy (TDS) or the like.

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

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

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

[0132] Furthermore, a peak of a concentration of a representative element is preferably located in a region from the surface of the positive electrode active material 100 to a depth of 3 nm in the direction of 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 process, in the case of a manufacturing process described later, the depth is approximately 2 nm to 5 nm from the surface of the positive electrode active material.

[0134] The third area 103, which is located within the first area 101 near a grain boundary, crystal defect or the like, also refers to an area where the concentration of a representative element, as 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 exhibits a concentration gradient, and a peak of fluorine concentration is preferably located in a region from the surface of the positive electrode active material 100 to a depth of 3 nm towards the center, more preferably to a depth of 1 nm, and even more preferably to a depth of 0.5 nm.

[0136] In this description and the like, the second region 102, present in a surface section of the positive electrode active material 100, refers to a region where the concentration of the second transition metal, detected by depth-directed analysis, is greater than or equal to half a peak. The second region 102, present within the first region 101 near a grain boundary, crystal defect, or the like, also refers to a region where the concentration of the second transition metal, detected by depth-directed analysis, is greater than or equal to half a peak. The analytical method used may include EDX line analysis, depth-directed analysis using ToF-SIMS, or the methods described above.

[0137] Thus, in some cases, the third region 103 and the second region 102 overlap. It should be noted that the third region 103 is preferably located in a region that is 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 located in a region that is 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 located in a region 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 towards the center, more preferably in a region from a depth of 0.5 nm or more to a depth of 3 nm or less.

[0139] The measurement range of XPS extends from the surface of the positive electrode active material 100 particle to 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. Similarly, the concentration of elements in the third region 103 and the second region 102, which are 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, the 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. Furthermore, the 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. Finally, the 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 compartment 101, the second compartment 102, and the third compartment 103 may each exhibit a concentration gradient; thus, the first compartment 101 may contain the element in the second compartment 102 or the third compartment 103, such as fluorine. Similarly, the third compartment 103 may contain the element in the first compartment 101 or the second compartment 102. Additionally, the first compartment 101, the second compartment 102, and the third compartment 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, lithium diffusion is difficult, whereas if the particle diameter is too small, it is difficult to maintain a crystal structure as described later. Therefore, D50 (also referred to as the mean 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 using a spray-drying device in a subsequent step, the nozzle diameter and the maximum particle diameter of the positive electrode active material 100 are preferably 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, leading to a reduction in the coverage capacity.

[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 to fill the spaces between the large particles with the small particles. Therefore, there can be two peaks in the particle size distribution.

[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 preferred range described above.

[0146] To promote grain growth at the time of baking, it is effective to adjust the ratio of lithium to the first transition metal of the starting material to a greater than 1, that is, to slightly increase the amount of lithium. For example, if the ratio of lithium 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 readily obtained. It should be noted that, as described later, lithium can 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 obtained positive electrode active material will 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 could be reduced.

[0148] Subsequently, the inventors of the present invention discovered that with the second area 102, which contains the second transition metal in the surface section, the particle size can be controlled in the preferred range by controlling the ratio of Li to the first transition metal, and a positive electrode active material with a high capacity retention rate can be formed.

[0149] In the positive electrode active material of an embodiment of the present invention, which comprises a region containing the second transition metal in the surface section, 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 can 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] A liquid-phase process, such as a sol-gel process, a solid-phase process, a sputtering process, an evaporation process, a chemical vapor deposition (CVD) process, a pulsed laser deposition (PLD) process, or the like, can be used as a coating method for the material containing the second transition metal. This embodiment describes the case in which the sol-gel process is used, which can be carried out with uniform coverage at atmospheric pressure. <sol-gel-verfahren>

[0152] A method for forming a material containing the second transition metal using a sol-gel process 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. 4A-1 denotes M2 as the alkoxide of the second transition metal. R represents an alkyl group with 1 to 18 carbon atoms or a substituted or unsubstituted aryl group with 6 to 13 carbon atoms. Although Fig. Figure 4A-1 shows the general formula in which the second transition metal has a valence (valency) of 4, but 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 employed as a second transition metal. R in Fig. 4A-2 represents an alkyl group with 1 to 18 carbon atoms or a substituted or unsubstituted aryl group with 6 to 13 carbon atoms.

[0156] The titanium alkoxide used can be tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetra-i-propoxytitanium (also known as 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.

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

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

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

[0161] Then particle 110 is collected and the alcohol is evaporated. The details of the training procedure will be described later.

[0162] It should be noted that this embodiment describes an example 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 has been formed on the positive electrode current collector, both the positive electrode current collector and the positive electrode active material layer can 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 process, a solid-phase process, a liquid-phase process such as a sol-gel process, or the like. However, the inventors of the present invention 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 the mixture is then heated, the representative element is segregated on a surface section of the positive electrode active material particle to form the third region 103. They have also found that with the third region 103 formed in this way, the positive electrode active material 100 exhibits excellent cycling properties.

[0164] In the case where the third region 103 is formed by heating as described above, the heating is preferably carried out after the particle of the composite oxide 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 the heating is carried out.

[0165] Segregation models of the representative element are developed with reference to Fig. 5A to 5C and Fig. 6A to 6D are described. It is likely that the segregation model of the representative element, such as magnesium, differs slightly depending on the ratio between lithium and the first transition metal present 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, i.e., the amount of lithium is small, is described with reference to Fig. Sections 5A to 5C are described. Additionally, a segregation model is presented in which the ratio of Li to the first transition metal in the starting material is greater than or equal to 1.03, i.e., the amount of lithium is large, with reference to Fig. Sections 6A to 6D are described. These segregation models in Fig. 5A to 5C and Fig. 6A to 6D, the first transition metal is cobalt, the second transition metal is titanium, and the representative element is magnesium.

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

[0167] It is generally known that during the synthesis of particles of the compound oxide containing lithium, cobalt, magnesium, and fluorine, some lithium migrates from the system (the particle on which lithium is formed). This occurs because lithium volatilizes during baking, elutes when the starting material is mixed with a solvent, and so on. Consequently, the Li to Co ratio in particle 110 of the compound oxide containing lithium, cobalt, magnesium, and fluorine is, in some cases, lower than the Li to Co ratio in the starting material.

[0168] If 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 particle 110, and cobalt oxide is readily produced. Thus, as in Fig. 5A shows the surface of particle 110 of the composite oxide in some cases covered with a cobalt oxide (CoO) layer 114.

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

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

[0171] Next, particle 110, which is coated with the titanium-containing layer 112, is heated. Although the details of the heating conditions will be described later, for example Fig. 5C represents 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. Simultaneously, magnesium and fluorine, contained in the region 111, are segregated at 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. Magnesium oxide also exhibits a rock salt crystal structure. Thus, it is likely that magnesium, in its state as magnesium oxide on the surface of particle 110, is more stable than in its interior. This could explain why magnesium segregates on the surface of particle 110 when the particle is heated.

[0173] Furthermore, it is assumed that fluorine contained in the starting material promotes the segregation of magnesium.

[0174] Fluorine has a higher electronegativity than oxygen. Therefore, even in a stable compound like magnesium oxide, the addition of fluorine is likely to result in an unequal charge distribution and a weakened bond between magnesium and oxygen. Furthermore, it is likely that oxygen will be replaced by fluorine in the magnesium oxide, causing the magnesium to move closer to 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 the magnesium oxide decreases. It is assumed that the lowering of the melting point causes magnesium to move slightly upon heating, thus facilitating segregation.

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

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

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

[0179] Next, the case in which 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. Sections 6A to 6D are described. Fig. Figure 6A presents a model diagram of the environment surrounding particle 120 of the composite oxide containing lithium, cobalt, magnesium, and fluorine, which is formed in a Li to Co ratio of greater than or equal to 1.03 in the starting material. 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 of the compound oxide of lithium, cobalt, magnesium and fluorine or the like, lithium diffuses from the interior of the particle 120 to its surface to compensate for this; as a result, a cobalt oxide layer is not readily formed on the surface.

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

[0182] Fig. 6C represents the state in which the particle 120 coated with the titanium-containing layer 122 is in Fig. 6B begins to be heated. Upon heating, titanium diffuses from the titanium-containing layer 122 into the interior of particle 110. The diffused titanium binds to the lithium contained in region 121 to form 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 shows that a cobalt oxide layer 124 is temporarily formed on the surface of the particle 120.

[0184] Fig. 6D represents the state in which heating occurs 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 has a rock salt crystal structure on its surface, it is assumed that magnesium, in the state where it exists as magnesium oxide on the surface of the particle 120, is more stable than in the state where it exists inside the particle 120. As in the case of Fig. As shown in 5A to 5C, fluorine promotes the segregation of magnesium.

[0185] As in Fig. As shown in 6D, magnesium and fluorine contained in region 121 are 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 area 103, which contains magnesium oxide and cobalt oxide, the second area 102, which contains lithium titanate, and the first area 101, which contains lithium cobaltate.

[0187] It should be noted that if the representative element is segregated by heating, and the compound oxide containing lithium and the first transition metal, located in the first region 101, is a polycrystal or exhibits crystal defects, the representative element may be segregated not only in the surface section but also near a grain boundary of the compound 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 may contribute to a further improvement in the stability of the crystal structure of the compound oxide containing lithium and the first transition metal, located in the first region 101.

[0188] If the composite oxide containing lithium and the first transition metal, located in the first region 101, has a crack, the representative element is also segregated in the crack upon heating. Additionally, not only the representative element but also the second transition metal can be segregated. The crack is in contact with the electrolyte solution, similar to the particle's surface. Thus, the representative element and the second transition metal are segregated in the crack, creating the third region 103 and the second region 102, resulting in a chemically stable material for the area in contact with the electrolyte solution. Consequently, 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 the range of T:F = 1:x (1.5 ≤ x ≤ 4) (atomic ratio), since the 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 created by epitaxial growth, the orientations of crystals in the second region 102 and the third region 103 are, in some cases, partially and substantially aligned with each other. That is, the second region 102 and the third region 103 become a topotaxic region in some cases. If 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 starting material, need to be segregated in the third area 103. For example, the first area 101 may contain a small amount of a representative element, such as magnesium. <Vierter Bereich 104>

[0192] As in Fig. As shown in Figure 1C, the positive electrode active material 100 can also have a fourth region 104 on the third region 103. If the positive electrode active material 100 furthermore has a defect, such as a crack segment 106, the fourth region 104 can be present to be embedded in the defect, such as the crack segment 106.

[0193] The fourth section, 104, contains some elements that are also found in the second section, 102, and the third section, 103. For example, the fourth section, 104, contains the second transition metal and the representative element.

[0194] The fourth region 104 can have a protrusion, a striped shape, or a layered form. The fourth region 104 is formed using the second transition metal and the representative element not present in the second region 102 or the third region 103 containing the second transition metals, as well as the representative elements present in the starting material, etc. That is, the fourth region 104 allows the amount of the second transition metal and the representative element present in the second region 102 and the third region 103 to be maintained within a suitable range, and in some cases, the crystal structures of the second region 102 and the third region 103 can be stabilized. Furthermore, the fourth region 104 can be used to repair defects, such as the crack section 106, present in the positive electrode active material 100.

[0195] The presence and shape of fourth region 104 can be observed using a scanning electron microscope (SEM) or similar instrument. Elements contained within fourth region 104 can be analyzed using SEM-EDX or similar techniques. [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, raw materials are produced. From the raw materials produced in this process, the first area 101 and the third area 103 are eventually formed.

[0198] As materials for lithium and the first transition metal contained in the first section 101, a lithium source and a source of the first transition metal are produced. Additionally, for the materials of the compound of representative elements contained in the third section 103, a source of the representative element is produced.

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

[0200] Lithium carbonate and lithium fluoride, for example, can be used as sources of lithium. An oxide of the first transition metal, for example, can be used as a source of the first transition metal. An oxide of the representative element contained in the third section and fluorine of the representative element contained in the third section, for example, can be used as sources of the representative element.

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

[0202] The amount of fluorine contained in the fluorine source is preferably 1.0 to 4 times (atomic ratio), more preferably 1.5 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 first transition metal source, and the representative element source are mixed. The fluorine source is preferably added as well. 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 initial heating. The heating is preferably carried out at a temperature higher than or equal to 800 °C and lower than or equal to 1100 °C, and more preferably at a temperature higher than or equal to 900 °C and lower than or equal to 1000 °C. The heating time is preferably longer than or equal to 2 hours and shorter than or equal to 20 hours. The baking is preferably carried out in a dry atmosphere, such as dry air. In the dry atmosphere, for example, the dew point is preferably lower than or equal to -50 °C, and more preferably lower than or equal to -100 °C. In this embodiment, the heating is carried out for 10 hours at 1000 °C, the temperature rise rate is 200 °C / h, and dry air, whose dew point is -109 °C, flows at a rate of 10 l / min.Afterwards, the heated materials are cooled to room temperature.

[0205] By 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 point, 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 been segregated on the surface of the composite oxide.

[0206] Additionally, pre-synthesized particles of the compound oxide 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 compound oxide of lithium and the first transition metal is cooled to room temperature. Then, the surface of the lithium-first transition metal compound oxide particle is coated with a material containing the second transition metal. In this training example, a sol-gel process is used.

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

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

[0210] Next, the above mixed solution is stirred in an atmosphere containing water vapor. Stirring can be carried out, for example, with a magnetic stirrer. The stirring time is not limited as long as the water and TTIP undergo a hydrolysis and polycondensation reaction in the atmosphere. For example, stirring can be carried out for 4 hours at 25 °C and 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 compared to the case where liquid water is added. Alternatively, when titanium alkoxide and water react with each other at room temperature, a sol-gel reaction can also proceed more slowly compared to the case where heating is carried out at a temperature above the boiling point of the alcohol, which is a solvent. A sol-gel reaction proceeds slowly, thus forming a high-quality coating layer containing titanium of a uniform thickness.

[0212] Following the preceding process, the precipitate is collected from the mixed solution. Filtration, centrifugation, evaporation and drying, or similar methods can be used for collection. In this embodiment, filtration is employed. 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 the second heating. During heating, the residence time in a specified temperature range is preferably less than or equal to 50 hours, more preferably longer than or equal to 2 hours and less than or equal to 10 hours, and even more preferably longer 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 form because the diffusion of the second transition metal will proceed too rapidly.

[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, causing the composite oxide particle to decompose, that a layered structure of lithium and the first transition metal in the composite oxide particle cannot be maintained, and so on.

[0216] In this embodiment, the specified temperature is 800 °C and is 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] The heating in step 15 causes the compound oxide of lithium and the first transition metal and the oxide of the second transition metal covering the compound oxide to form a topotaxy. In other words, the first region 101 and the second region 102 become a topotaxy.

[0218] During the heating process in step 15, the representative elements, which form a solid solution within the composite oxide particle of lithium and the first transition metal, are unevenly distributed across 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 point, 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 topotaxic region.

[0219] Since the second region 102 and the third region 103 contain crystals whose orientations are substantially aligned and which have a stable bond with the first region 101, changes 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 section with its 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 area 101 and the entire second area 102 need not become a topotaxy as long as part of the first area 101 and part of the second area 102 do become a topotaxy. Furthermore, the entire second area 102 and the entire third area 103 need not become a topotaxy as long as part of the second area 102 and part of the third area 103 do become a topotaxy.

[0221] If the compound 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 an embodiment of the present invention, after the elements forming the second region 102 have been coated, heating is carried out 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 to say, in general, two coating steps are required to provide two types of regions in one surface section; however, in the method for forming the positive electrode active material of an embodiment of the present invention, only one coating step (sol-gel process) is required, which is a highly productive 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, as this facilitates the generation of topotaxy. 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. The positive electrode active material 100, comprising the first region 101, the second region 102, and the third region 103, can be formed by the preceding process.

[0226] This embodiment can be implemented in a suitable combination with any of the other embodiments. (Version 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 preceding embodiment are described. As an example, this embodiment describes a secondary battery in which a positive electrode, a negative electrode, and an electrolyte solution are wrapped in an outer part. [Positive electrode]

[0228] The positive electrode comprises 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] The positive electrode active material 100, described in the preceding embodiment, can be used. Using the positive electrode active material 100 described above, 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, relative to the total amount of the active material layer, 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.%.

[0232] An electrical conduction network can be formed by the conductive additive in the active material layer. The conductive additive also enables the maintenance of an electrical conduction path 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 conductive additives include natural graphite, synthetic graphite such as mesocarbon microbeads, and carbon fiber. Examples of carbon fibers include mesophase pitch-based carbon fiber, isotropic pitch-based carbon fiber, carbon nanofiber, and carbon nanotube. A carbon nanotube can be formed, for example, by a vapor deposition process. Other examples of conductive additives include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite (cracked lead) particles, graphene, and fullerene. Alternatively, a metal powder or metal fibers of copper, nickel, aluminum, silver, gold, or the like, a conductive ceramic material, or the like can 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 has a planar shape. A graphene compound enables low-resistance surface contact. In addition, in some cases, a graphene compound exhibits extremely high conductivity even at low thicknesses, thus enabling the efficient formation of a conduction path in an active material layer, even in small quantities. For this reason, it is preferred to use a graphene compound as a conductive additive, as the area in contact between the active material and the conductive additive can be increased.The graphene compound, which serves 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, thereby reducing the electrical resistance. For example, graphene, multilayer graphene, or RGO is particularly preferably used as the graphene compound. It should be noted that RGO refers to a compound obtained, for example, by the reduction of graphene oxide (GO).

[0236] In cases where an active material with a small particle diameter (e.g., 1 µm or less) is used, the specific area of ​​the active material is large, and therefore more conduction paths are required for the active material particles. Thus, the amount of conductive additive tends to increase, and the amount of active material supported tends to decrease relative to this. As the amount of active material supported decreases, so does the capacity of the secondary battery. In such cases, a graphene compound, which can efficiently form a conduction path even in small quantities, is particularly preferred as a conductive additive because it does not reduce the amount of active material supported.

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

[0238] Fig. Figure 7A shows a longitudinal cross-sectional view of the active material layer 200. The active material layer 200 comprises positive electrode active material particles 100, a graphene compound 201 serving as a conductive additive, and a binder (not shown). The graphene compound 201 can be, for example, graphene or multilayer graphene. The graphene compound 201 preferably has a sheet-like shape. The graphene compound 201 can have a sheet-like shape formed from several layers of multilayer graphene and / or several 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 represented by thick lines in Fig. Figure 7B shows that these are actually thin films, each with a thickness corresponding to that of one or more layers of carbon molecules. The multitude of graphene compounds 201 are configured such that they partially cover or adhere to the surfaces of the multitude 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, numerous graphene compounds are interconnected to form a network-like graphene compound layer (hereinafter referred to as the graphene compound network or graphene network). The graphene network covering the active material can act as a binder to hold the active materials in place. The amount of binder required can therefore be reduced, or the binder may even be unnecessary. This can increase the proportion of active material in terms of electrode volume or weight, thus increasing the capacity of the secondary battery.

[0241] Here, it is preferred to carry out the reduction after a layer, which becomes the active material layer 200, has been formed such that graphene oxide is used as the graphene compound 201 and mixed with an active material. If graphene oxide with extremely high dispersibility in a polar solvent is used to form the graphene compounds 201, the graphene compounds 201 can be dispersed substantially uniformly in the active material layer 200. The solvent is removed by volatilization from a dispersion medium in which the 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 as to establish surface contact, thereby forming a three-dimensional conduction path.It should be noted that graphene oxide, for example, can be reduced either by heat treatment or by using a reducing agent.

[0242] Unlike a particle-shaped conductive additive, such as carbon black, which makes 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 in the case of a normal conductive additive. This increases the proportion of the positive electrode active material particles 100 in the active material layer 200, resulting in an 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. Subsequently, a graphene compound can be added during the formation of the positive electrode active material layer to improve the conduction path between the active materials.

[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] Water-soluble polymers are preferably used as the binder. These water-soluble polymers can be polysaccharides or similar materials. The polysaccharide can be a cellulose derivative, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, or regenerated cellulose, starch, or similar materials. It is particularly preferred that such water-soluble polymers are used in combination with one of the aforementioned rubber materials.

[0246] Alternatively, a binder 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 monomer, polyvinyl acetate or nitrocellulose is preferably used.

[0247] Many of the above materials can be used in combination as a binder.

[0248] For example, a material with a significant viscosity-modifying effect and another material can be used in combination. For example, a rubber material or the like may have high adhesion or high elasticity, but may exhibit difficulties in mixing with a solvent when modifying its viscosity. In such a case, for example, a rubber material or the like is preferably mixed with a material that has a significant viscosity-modifying effect. A water-soluble polymer is preferably used as the material with a significant viscosity-modifying effect. An example of a water-soluble polymer with a particularly significant viscosity-modifying effect is the polysaccharide mentioned above; for example, a cellulose derivative, such as...Carboxymethylcellulose (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 or ammonium salt of carboxymethylcellulose, and thus readily acts as a viscosity modifier. This high solubility can also enhance the dispersibility of an active material and other components when forming a slurry for an electrode. In this description, cellulose and a cellulose derivative used as an electrode binder are defined as salts thereof.

[0250] The water-soluble polymers stabilize the viscosity by dissolving in water and enable a stable dispersion of the active material and any other material combined as a binder, such as styrene-butadiene rubber, in an aqueous solution. Furthermore, a water-soluble polymer is expected to adsorb readily and stably onto the surface of the active material due to its functional group. Many cellulose derivatives, such as carboxymethylcellulose, possess functional groups, such as hydroxyl and carboxyl groups. Because of these functional groups, polymers are expected to interact with each other and cover a large area of ​​the active material's surface.

[0251] In cases where the binder covering or in contact with the surface of the active material forms a film, this film is expected to act as a passivation film to suppress the decomposition of the electrolyte solution. Here, the passivation film is defined as a film with no electrical conductivity or a film with very low electrical conductivity. The passivation film can prevent the decomposition of an electrolyte solution at a potential at which a battery reaction occurs, for example, when the passivation film forms 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 constructed using a material with high conductivity, such as a metal like stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferred that the material used for the positive electrode current collector does not dissipate at the positive electrode potential. Alternatively, the positive electrode current collector can be constructed using an aluminum alloy to which an element for improving heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, has been added. As a further alternative, a metallic element that forms a silicide by reacting with silicon can be used. Examples of metallic elements that form a silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.The current collector can have any number of different 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 via an alloying reaction and a demalloying 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 one of the aforementioned 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, La3Co2Sn-, CoSb3, InSb and SbSn.An element that enables charge / discharge reactions through an alloying reaction and an alloying reaction with lithium, a compound containing the element, and the like can be referred to as an alloy-based material.

[0256] In this description and similar contexts, SiO₂ refers, for example, to silicon monoxide. SiO₂ can alternatively be represented by SiO₂. x The representation is shown. 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] Carbon-based materials that can be used include graphite, graphitizing carbon (soft carbon), non-graphitizing carbon (hard carbon), carbon nanotubes, graphene, carbon black, and the like.

[0258] Examples of graphite include artificial and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite, which has a spherical shape, can be used as artificial graphite. For example, MCMB are preferred because they can have a spherical shape. Furthermore, MCMB are preferred because they can relatively easily be produced with a small surface area. Examples of natural graphite include lamellar graphite and spherical natural graphite.

[0259] Graphite has a low potential, essentially the same as that of a lithium metal (higher than or equal to 0.05 V and lower than or equal to 0.3 V vs. Li / Li). + This occurs when lithium ions are intercalated into the graphite (during the formation of a lithium-graphite intercalation compound). For this reason, a lithium-ion secondary battery can operate at a high voltage. Additionally, graphite is preferred over lithium metals due to its advantages, such as its relatively high capacity per unit volume, relatively low volume expansion, low cost, and higher level of safety.

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

[0261] Another alternative for the negative electrode active material Li 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 / cm²). 3 ) preferred.

[0262] A nitride containing lithium and a transition metal is preferably used, in which 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 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-extracting 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 alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used. Other examples of materials that cause a conversion reaction include oxides, such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, and sulfides, such as CoS₂. 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 binder that may be included in the negative electrode active material layer, materials may be used that are similar to those of the conductive additive and binder that may be included in the positive electrode active material layer. <negativelektrodenstromkollektor>

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

[0266] The electrolyte solution contains a solvent and an electrolyte. An aprotic organic solvent is preferably used as the solvent for the electrolyte solution. For example, one of the following solvents may be used: 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, methyldiglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone, or two or more of these solvents may be used in a suitable combination and ratio.

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

[0268] A lithium salt, such as LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, Lil, Li2SO4, Li2B, can be used as the electrolyte, which is dissolved in the solvent described above. 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 can be used, or two or more of these lithium salts can be used in a suitable combination in a suitable ratio.

[0269] The electrolyte solution used for a secondary battery is preferably highly purified and contains only a small amount of dust particles and elements other than the constituents of the electrolyte solution (hereinafter also simply referred to as impurities). In particular, 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 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 the added material, relative to the total solvent, is, for example, greater than or equal to 0.1 wt% and less than or equal to 5 wt%.

[0271] Alternatively, a gelled electrolyte can be used, which is obtained by allowing a polymer to swell in an electrolyte solution.

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

[0273] The polymer that undergoes gelation can be 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.

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

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

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

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

[0278] Deterioration of the separator during charging and discharging at high voltage can be suppressed, thus improving the reliability of the secondary battery, as oxidation resistance is enhanced when the separator is coated with a ceramic-based material. Furthermore, coating the separator with a fluorine-based material facilitates close contact with the electrode, resulting in high output characteristics. Coating the separator with a polyamide-based material, particularly aramid, improves the safety of the secondary battery due to enhanced heat resistance.

[0279] For example, both surfaces of a polypropylene film can be coated with a mixed material of aluminum oxide and aramid. Alternatively, one surface of the polypropylene film in contact with the positive electrode can be coated with the mixed material of aluminum oxide and aramid, and one 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-layered structure, the capacity of the secondary battery per volume can be increased, as the safety of the secondary battery can be maintained even if the overall thickness of the separator is small. [Outdoor part]

[0281] For an external component contained within the secondary battery, a metal material, such as aluminum, and a resin material can be used, for example. An external component in the form of a film can also be used. This film could, for instance, have a three-layer structure, consisting of a highly flexible thin metal film made of aluminum, stainless steel, copper, nickel, or similar materials, layered over a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide. An insulating synthetic resin film, such as one made of a polyamide-based resin or a polyester-based resin, forms the outer surface of the external component, positioned over the thin metal film. [Charging and unloading procedures]

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

[0283] First, constant current (CC) charging, which is one of the charging methods, is described. CC charging is a charging method in which a constant current flows to a secondary battery throughout the entire charging period, and charging stops when the voltage reaches a predetermined level. The secondary battery is assumed to be an equivalent circuit with an internal resistance R and a secondary battery capacity or capacitor C, as shown in Fig. 8A is shown. 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 is shown, 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 thus also constant. In contrast, the voltage V applied to the secondary battery capacity C increases. C over time. Accordingly, the secondary battery voltage V increases. B over time.

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

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

[0287] Next, a CCCV charge is described, which is a charging method that differs from the one described above. The CCCV charge is a charging method in which a CC charge is performed until the voltage reaches a predetermined voltage, and then a constant voltage charge (CV charge) is performed until the current becomes small, specifically a final current value.

[0288] During the CC charge, a switch of a constant current source is on and a switch of a constant voltage source is off, as shown in Fig. 9A is shown, 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 thus also constant. In contrast, the voltage V applied to the secondary battery capacity C increases. C over time. Accordingly, the secondary battery voltage V increases. B over time.

[0289] If the secondary battery voltage V B When a predetermined voltage is reached, e.g., 4.3 V, the switch from constant current (CC) charging to constant voltage (CV) charging is performed. During CV charging, the constant voltage source switch is on and the constant current source switch is off, as shown in... Fig. 9B is shown; 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 If the condition is met, the voltage V applied to the internal resistance R R decreases over time. When the voltage V applied to the internal resistance R R As the current decreases, so does the current I flowing to the secondary battery, according to Ohm's law (V). R = R × I) from.

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

[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 performed, and after the CCCV charge has ended. Even after the CCCV charge has ended, the secondary battery voltage V B hardly at all. < <cc-entladung>>

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

[0293] Fig. Figure 10 shows an example of the secondary battery voltage V B and the discharge current while the constant current (CC) discharge is performed. As the discharge progresses, the secondary battery voltage V decreases. 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 units of 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 2X A is rewritten as follows: The discharge is performed at 2 C. The case where discharging is performed at a current of X / 5 A is rewritten as follows: The discharge is performed at 0.2 C. The case where charging is performed at a current of 2X A is similarly rewritten as follows: The charge is performed at 2 C, and the case where charging is performed at a current of X / 5 A is rewritten as follows: The charge is performed at 0.2 C. (Version 3)

[0295] This embodiment describes examples of a secondary battery form that contains the positive electrode active material 100 described in the preceding embodiment. For the materials used in the secondary battery described in this embodiment, reference can be made to the description of the preceding 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. Figure 11B is a cross-sectional view of it.

[0297] In a button cell secondary battery 300, a positive electrode socket 301, which also serves as the positive electrode terminal, and a negative electrode socket 302, which also serves as the negative electrode terminal, are insulated and sealed from each other by a seal 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, which is 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, which is 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 box 301 and the negative electrode box 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 box 301 and the negative electrode box 302 are preferably coated with nickel, aluminum, or the like to prevent corrosion due to the electrolyte solution. The positive electrode box 301 and the negative electrode box 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 described in Fig. As shown in Figure 11B, the positive electrode 304, the separator 310, the negative electrode 307, and the negative electrode housing 302 are arranged one above the other in that order, with the positive electrode housing 301 at the bottom, and the positive electrode housing 301 and the negative electrode housing 302 are connected under pressure, with the seal 303 between them. In this way, the button cell secondary battery 300 can be manufactured.

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

[0302] Here, the current flow during the charging of a secondary battery is described with reference to... Fig. 11C described. When a secondary battery using lithium is considered a closed circuit, lithium ions move in the same direction as the current. It should be noted that in a secondary battery using lithium, the anode and cathode exchange roles during charging and discharging, and an oxidation and a reduction reaction take place on the respective 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 description, 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, discharging, reverse pulse current, and charging current are applied.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 switch roles during charging and discharging. Therefore, the terms "anode" and "cathode" are not used in this description. If the term "anode" or "cathode" is used, it should always be specified whether the charging or discharging process involves the anode or the cathode, and which electrode corresponds to a positive (plus) or negative (minus) electrode.

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

[0304] Next, an example of a cylindrical secondary battery will be given with reference to Fig. 12A to 12D described. A cylindrical secondary battery 600 contains, as described in Fig. Figure 12A shows a positive electrode cap (battery cover) 601 on the uppermost surface and a battery box (outer box) 602 on the side surface and the downward-facing surface. The positive electrode cap and the battery box (outer box) 602 are insulated from each other by a seal (insulating seal) 610.

[0305] Fig. Figure 12B is a schematic cross-sectional view of the cylindrical secondary battery. Within the battery housing 602, which has a hollow cylindrical shape, a battery cell is provided in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound, with a strip-shaped separator 605 between them. Although not shown, the battery cell is wound around a central pin. One end of the battery housing 602 is closed, and its other end is open. The battery housing 602 can be made of a metal that exhibits 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).Alternatively, the battery housing 602 is preferably coated with nickel, aluminum, or the like to prevent corrosion due to the electrolyte solution. Inside the battery housing 602, the battery cell, in which the positive electrode, the negative electrode, and the separator are wound, is arranged between a pair of opposing insulating plates 608 and 609. Furthermore, a non-aqueous electrolyte solution (not shown) is injected into the battery housing 602 containing the battery cell. A non-aqueous electrolyte solution similar to that used in button cell secondary batteries can be used.

[0306] Since the positive and negative electrodes 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 collector) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector) 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 metallic 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 to the bottom of the battery housing 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 acts as a heat-sensitive resistor whose resistance increases with temperature, limits the current by increasing its resistance. A barium titanate (BaTiO3)-based semiconductor ceramic can be used for the PTC element.

[0307] Alternatively, as in Fig. Figure 12C shows a plurality of secondary batteries 600 arranged between a conductive plate 613 and a conductive plate 614 to form a module 615. The plurality of secondary batteries 600 can be connected in parallel, in series, or in series after being connected in parallel. A large amount of electrical energy can be drawn from the module 615 comprising the plurality of secondary batteries 600.

[0308] Fig. Figure 12D is a top view of module 615. The conductive plate 613 is shown with a dashed line for clarity. As in Fig. As shown in Figure 12D, the module 615 can include a conductor 616 that electrically connects the multiple secondary batteries 600. The conductive plate 613 can be positioned over the conductor 616 so that they overlap. Additionally, a temperature control device 617 can be provided between the multiple secondary batteries 600. If the secondary batteries 600 become overheated, the temperature control device 617 can cool them, and if they become too cold, the temperature control device 617 can heat them up. Thus, the performance of the module 615 is not so easily affected by the ambient air temperature.

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

[0310] Further structural examples for 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 as well Fig. 16 described.

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

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

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

[0314] The linewidth of antenna 914 is preferably larger than that of antenna 915. This can 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. Layer 916 has a function, for example, of blocking an electromagnetic field from the secondary battery 913. A magnetic body can be used as layer 916, for example.

[0316] It should be noted that the structure of the secondary battery is not based on the one in Fig. 13A and Fig. The section shown in 13B is limited.

[0317] For example, as in Fig. 14A-1 and Fig. 14A-2 shows two opposing surfaces of the secondary battery 913 in Fig. 13A and Fig. 13B must be equipped with respective antennas. Fig. 14A-1 is an exterior view showing one side of the opposite surfaces, and Fig. 14A-2 is an exterior view showing the other side of the opposite surfaces. For sections that are in Fig. 13A and Fig. 13B are similar, a description of the in Fig. 13A and Fig. Reference is made to the secondary battery shown in 13B.

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

[0319] The structure described above allows for the enlargement of both antenna 914 and antenna 918. Antenna 918, for example, incorporates a function for data communication with an external device. An antenna with a shape that can be adapted to antenna 914 can, for instance, be used as antenna 918. A communication system using antenna 918 between the secondary battery and another device could employ a response method that can be used between the secondary battery and another device, such as NFC.

[0320] Alternatively, as in Fig. 14B-1 shows the secondary battery 913 in Fig. 13A and Fig. 13B shall 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 where the display device 920 is located. For sections corresponding to those in Fig. 13A and Fig. 13B are similar, a description of the in Fig. 13A and Fig. Reference is made to the secondary battery shown in 13B.

[0321] The display device 920 can, for example, display an image showing whether charging is currently taking place, an image showing the amount of stored energy, or the like. Electrical paper, a liquid crystal display device, an electroluminescent (EL) display device, or the like can be used as the display device 920. For example, the use of electrical paper can reduce the power consumption of the display device 920.

[0322] Alternatively, as in Fig. 14B-2 shown, the secondary battery 913 in Fig. 13A and Fig. 13B shall be equipped with a sensor 921. The sensor 921 is electrically connected to terminal 911 via terminal 922. For sections that correspond to the one in Fig. 13A and Fig. 13B are similar, a description of the in Fig. 13A and Fig. Reference is made to the secondary battery shown in 13B.

[0323] The sensor 921, for example, has a function for measuring displacement, position, velocity, 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 radiation. The sensor 921 can, for example, determine data about the environment (e.g., temperature) in which the secondary battery is located and store this data in a memory within the circuit 912.

[0324] Furthermore, structural examples for the secondary battery 913 are given with reference to Fig. 15A and Fig. 15B as well Fig. 16 described.

[0325] The in Fig. The secondary battery 913 shown in Figure 15A comprises a wound part 950, which is provided with terminals 951 and 952 in a housing 930. The wound part 950 is immersed in an electrolyte solution within the housing 930. Terminal 952 is in contact with the housing 930. An insulator or the like prevents contact between terminal 951 and the housing 930. It should be noted that Fig. Figure 15A represents the housing 930, which is shown divided into two pieces for simplicity; however, in the actual structure, the wound part 950 is covered by 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 shown, the 930 case in Fig. 15A can be constructed using a variety of materials. In the case of the secondary battery 913 in Fig. For example, in 15B, a housing 930a and a housing 930b are attached to each other, and the wound part 950 is arranged in an area enclosed by the housing 930a and the housing 930b.

[0327] For housing 930a, an insulating material, such as an organic resin, can be used. In particular, if a material such as an organic resin is used for the side on which an antenna is formed, it can prevent the electric field from being blocked by the secondary battery 913. If the electric field is only minimally blocked by housing 930a, an antenna, such as antenna 914 or antenna 915, can be arranged inside housing 930. For housing 930b, for example, a metal material can be used.

[0328] Fig. Figure 16 illustrates the structure of the wound part 950. The wound part 950 comprises a negative electrode 931, a positive electrode 932, and separators 933. The wound part 950 is obtained by winding a film web from a stack in which the negative electrode 931 overlaps the positive electrode 932, with the separator 933 positioned between them. It should be noted that a plurality of film webs, each containing the negative electrode 931, the positive electrode 932, and the separator 933, can be stacked on top of each other.

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

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

[0331] Next, an example of a laminated secondary battery will be given with reference to Fig. 17A to 17C, Fig. 18A and Fig. 18B, Fig. 19, Fig. 20, Fig. 21A to 21C, Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D as well Fig. 23A and Fig. 23B described. If 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 along with the electrical device.

[0332] A laminated secondary battery 980 is described with reference to Fig. 17A to 17C described. The laminated secondary battery 980 comprises a Fig. The wound part 993 shown in Figure 17A comprises a negative electrode 994, a positive electrode 995, and a separator 996. The wound part 993 is, just like the one shown in Figure 17A, Fig. 16 shown wound part 950, 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 in between.

[0333] It should be noted that the number of foil webs, each comprising the negative electrode 994, the positive electrode 995, and the separator 996, is determined appropriately according to the required capacitance 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 terminal electrode 997 and the terminal electrode 998.

[0334] As in Fig. As shown in Figure 17B, the wound part 993 is packed into a space formed by joining a film 981 and a film 982 with a recessed part by thermocompression bonds or the like, which serve as the outer part, whereby, as shown in Fig. As shown in Figure 17C, the secondary battery 980 can be formed. The wound part 993 comprises the terminal electrode 997 and the terminal electrode 998 and is immersed in an electrolyte solution within a space enclosed by the film 981 and the film 982 with a recessed part.

[0335] For film 981 and film 982 with a recessed section, a metallic material, such as aluminum, or a resin material can be used, for example. Using a resin material for film 981 and film 982 with a recessed section, the shapes of film 981 and film 982 with a recessed section can be changed when an external force is applied; in this way, a flexible secondary battery can be produced.

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

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

[0338] In Fig. In sections 17A to 17C, an example is described in which the secondary battery 980 comprises a wound part in a space formed by films that serve as the outer part; as in Fig. 18A and Fig. As shown in Figure 18B, a secondary battery can, however, comprise a multitude of strip-shaped positive electrodes, a multitude of strip-shaped separators, and a multitude of strip-shaped negative electrodes in a space formed by films that serve, for example, as an outer part.

[0339] A laminated secondary battery 500, which is in Fig. As shown in Figure 18A, the device comprises a positive electrode 503, which includes a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506, which includes a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte solution 508, and an outer part 509. The separator 507 is arranged between the positive electrode 503 and the negative electrode 506 in the outer part 509. The outer part 509 is filled with the electrolyte solution 508. The electrolyte solution described in embodiment 2 can be used for the electrolyte solution 508.

[0340] The laminated secondary battery 500, which is in Fig. As shown in Figure 18A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for an electrical contact with an outer section. For this reason, the positive electrode current collector 501 and the negative electrode current collector 504 can be arranged such that part of the positive electrode current collector 501 and part of the negative electrode current collector 504 are exposed on the outside of the outer part 509. Alternatively, a lead electrode can be attached to the positive electrode current collector 501 or the negative electrode current collector 504 by ultrasonic welding, so that instead of the positive electrode current collector 501 and the negative electrode current collector 504, the lead electrode is exposed on the outside of the outer part 509.

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

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

[0343] The example in Fig. The 18B battery comprises 16 electrode layers. The laminated secondary battery 500 exhibits flexibility despite having 16 electrode layers. Fig. 18B represents a structure comprising 8 layers of negative electrode current collectors 504 and 8 layers of positive electrode current collectors 501, i.e., a total of 16 layers. It should be noted that Fig. Figure 18B shows a cross-section of the negative electrode connection section, and the eight negative electrode current collectors 504 are connected by ultrasonic welding. It goes without saying that the number of electrode layers is not limited to 16 and can be greater or less than 16. A large number of electrode layers allows the secondary battery to have a high capacity. Conversely, a small number of electrode layers allows the secondary battery to have a thin profile and high flexibility.

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

[0345] Fig. Figure 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 in which part of the positive electrode current collector 501 is exposed (hereinafter referred to as the 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 in which part of the negative electrode current collector 504 is exposed, i.e., a tab region. The surfaces and shapes of the tab regions in the positive electrode and the negative electrode are not to be confused with those shown in Figure 21A. Fig. 21A can be shown, limited. [Method for manufacturing the laminated secondary battery]

[0346] An example of a method for manufacturing the laminated secondary battery, the exterior of which is 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. Figure 21B represents the layer arrangement comprising the negative electrode 506, the separator 507, and the positive electrode 503. The secondary battery described here as an example comprises 5 negative electrodes and 4 positive electrodes. The label areas of the positive electrodes 503 are then joined together, and the positive electrode terminal electrode 510 is attached to the label area of ​​the positive electrode located on the outermost surface. This joining or bonding can be carried out, for example, by ultrasonic welding. Similarly, the label areas of the negative electrodes 506 are joined together, and the negative electrode terminal electrode 511 is attached to the label area of ​​the negative electrode located on the outermost surface.

[0348] Then 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 shown in Fig. Figure 21C is shown. Next, the outer edges of the outer part 509 are joined together. This joining can be carried out, for example, by thermocompression bonding. A portion (or side) of the outer part 509 remains unbonded (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 connecting the two parts. The laminated secondary battery 500 can be manufactured in the manner described above.

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

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

[0353] Fig. 22A is a schematic top view of a flexible secondary battery 50. Fig. 22B1, Fig. 22B2 and Fig. 22C are schematic cross-sectional views along the section line C1-C2, the section line C3-C4 or the section line A1-A2 in Fig. 22A. The battery 50 comprises 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 represent the positive electrode 11a and the negative electrode 11b contained in the battery 50. Fig. Figure 23A is a perspective view showing the arrangement sequence of the positive electrode 11a, the negative electrode 11b and the separator 14. Fig. 23B is a perspective view showing line 12a and line 12b in addition to positive electrode 11a and negative electrode 11b.

[0355] As in Fig. As shown in Figure 23A, the battery 50 comprises 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 comprise a protruding label section and a section other than the label. A positive electrode active material layer is formed on a surface of the positive electrode 11a other than the label section, and a negative electrode active material layer is formed on a surface of the negative electrode 11b other than the label section.

[0356] The positive electrodes 11a and the negative electrodes 11b are arranged one above the other in such a way that the surfaces of the positive electrodes 11a, on 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 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, separator 14 is shown by a dashed line for easier viewing.

[0358] As in Fig. As shown in Figure 23B, the plurality of positive electrodes 11a is also electrically connected to the conductor 12a in a connecting section 15a. The plurality of negative electrodes 11b is electrically connected to the conductor 12b in a connecting section 15b.

[0359] Next, the outer part 51 will be 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 halfway between the facing sections of the outer part 51, with the positive electrodes 11a and the negative electrodes 11b positioned between them. The outer part 51 comprises a bent section 61, a pair of sealing sections 62, and a sealing section 63. The pair of sealing sections 62 is provided with the positive electrodes 11a and the negative electrodes 11b positioned between them and can therefore also be referred to as lateral seals. The sealing section 63 has sections that overlap with the lines 12a and 12b and can also be referred to as the top seal.

[0361] A portion of the outer part 51, which overlaps with the positive electrodes 11a and the negative electrodes 11b, preferably has a wave-like shape in which crest lines 71 and trough lines 72 are arranged alternately. The sealing sections 62 and the sealing section 63 of the outer part 51 are preferably flat.

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

[0363] The distance between an end section of the negative electrode 11b in the lateral direction and the sealing section 62 is referred to as distance La. If the shape of the battery 50 changes, e.g., by bending, the shape of the positive electrode 11a and the negative electrode 11b changes such that their positions are shifted relative to each other in the longitudinal direction, as will be 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 hard against each other 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 electrolyte 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 increases.

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

[0365] In particular, if the total thickness of the stacked positive electrodes 11a and negative electrodes 11b and separators 214 (not shown) is referred to as thickness t, the spacing 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, and even more preferably 1.0 times or more and 2.0 times or less of the thickness t. If the spacing La is in the range described above, a compact battery can be obtained that is very reliable when bent.

[0366] Furthermore, if a distance between the pair of sealing sections 62 is designated as distance Lb, the distance Lb is preferably sufficiently longer than a width Wb of the negative electrode 11b. In this case, the position of a portion of the positive electrode 11a and the negative electrode 11b can be shifted in the lateral direction even if the positive electrode 11a and the negative electrode 11b come into contact with the outer part 51 by changing the shape of the battery 50, for example by repeated bending; thus, it can be effectively prevented that the positive and negative electrodes 11a and 11b and the outer part 51 are rubbed against each other.

[0367] For example, the difference between the distance Lb (i.e., the distance between the pair of sealing sections 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, and 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 represents a cross-section encompassing the conductor 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 in Fig. As shown in Figure 22C, a space 73 is preferably provided between the end sections of the positive electrode 11a and the negative electrode 11b in the longitudinal direction and the outer part 51 in the bending section 61.

[0371] Fig. 22D is a schematic cross-sectional view of 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, part of the outer part 51, which is positioned on the outside during bending, remains straight, while another part, positioned on the inside, changes its shape as it shrinks. Specifically, the part of the outer part 51 that is positioned on the outside during bending changes its shape such that the wave amplitude becomes smaller and the length of the wave period becomes larger. Conversely, the part of the outer part 51 that is positioned on the inside during bending changes its shape such that the wave amplitude becomes larger and the length of the wave period becomes smaller. When the outer part 51 changes its shape in this way, the stress exerted on the outer part 51 by bending is mitigated, so that the material itself forming the outer part 51 does not have to expand and contract. As a result, the battery 50 can be bent with minimal force without damaging the outer part 51.

[0373] As in Fig. As shown in Figure 22D, the positions of the positive electrode 11a and the negative electrode 11b are displaced relative to each other when the battery 50 is bent. At this point, the ends of the stacked positive electrodes 11a and negative electrodes 11b are fixed on the side of the sealing section 63 by the fastening element 17. Thus, the multiple positive electrodes 11a and the multiple negative electrodes 11b are displaced more in a position closer to the bending section 61. Therefore, the stress exerted on the positive electrode 11a and the negative electrode 11b is reduced, and the positive electrode 11a and the negative electrode 11b themselves do not have 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 sections of the positive and negative electrodes 11a and 11b and the outer part 51, which allows the relative positions of the positive electrode 11a and the negative electrode 11b to be shifted, while the end sections of the positive electrode 11a and the negative electrode 11b, which are located on an inside when the battery 50 is bent, do not touch the outer part 51.

[0375] In the Fig. 22A, Fig. 22B1, Fig. 22B2, Fig. 22C and Fig. 22D as well Fig. 23A and Fig. In the battery 50 shown in Figure 23B, it is less likely that the outer part, the positive electrode 11a, and the negative electrode 11b will be damaged and that the battery characteristics will deteriorate, even if the battery 50 is repeatedly bent and straightened. If the positive electrode active material described in the preceding embodiment is used for the positive electrode 11a contained in the battery 50, a battery with improved cycle characteristics can be obtained. (Version 4)

[0376] This embodiment describes examples of electrical devices that include the secondary battery of an embodiment of the present invention.

[0377] First show Fig. 24A to 24G Examples of electrical devices that include the flexible secondary battery described in embodiment 3. Examples of an electrical device that includes a flexible secondary battery include television sets (also called TVs or TV receivers), computer monitors or the like, digital cameras or digital video cameras, digital photo frames, mobile phones (also called cell phones or portable telephones), portable gaming consoles, portable information terminals, audio playback devices, and large gaming machines, such as pachinko machines.

[0378] Furthermore, 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. Figure 24A provides an example of a mobile phone. A mobile phone 7400 is equipped with a display section 7402, which is built into a housing 7401, a control button 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. It should be noted that the mobile phone 7400 includes a secondary battery 7407. If the secondary battery of an 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. Figure 24B depicts the 7400 mobile phone, which is bent. If the entire 7400 mobile phone is bent by external force, the secondary battery 7407, which is contained in the 7400 mobile phone, will also be bent. Fig. Figure 24C represents the bent secondary battery 7407. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. It should be noted that the secondary battery 7407 includes a terminal electrode 7408, which is 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 exhibit high reliability even in a bent state.

[0381] Fig. Figure 24D represents an example of a display device in the form of a wristband. A portable display device 7100 comprises a housing 7101, a display section 7102, an operating knob 7103, and a secondary battery 7104. Fig. 24E represents 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 or all of the secondary battery 7104 changes. It should be noted that the radius of curvature of a curve at a point is the radius of the circular arc that most closely approximates the curve at that point. The reciprocal of the radius of curvature is the curvature. Specifically, part of the casing, the entire casing, part of the main surface, or the entire main surface of the secondary battery 7104 changes within the range of the radius of curvature from 40 mm to 150 mm. If the radius of curvature of the main surface of the secondary battery 7104 is greater than or equal to 40 mm and less than or equal to 150 mm, a high level of reliability can be maintained.When the secondary battery of an embodiment of the present invention is used as secondary battery 7104, a lightweight portable display device with a long service life can be provided.

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

[0383] The portable information terminal 7200 can run 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 display section 7202 is curved, and images can be displayed on this curved surface. Display section 7202 also includes a touch sensor, and operation can be performed by touching the screen with a finger, a stylus, or the like. For example, touching an icon 7207 displayed on display section 7202 can launch an application.

[0385] The 7205 control knob can perform various functions, such as time setting, power on / off, wireless communication on / off, sleep mode activation / deactivation, and power saving mode activation / deactivation. For example, the functions of the 7205 control knob can be customized by adjusting the operating system built into the 7200 portable information terminal.

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

[0387] The 7200 portable information terminal also includes the 7206 input / output connector, and data can be sent directly to and received from another information terminal via a connecting element. Charging is also possible via the 7206 input / output connector. It should be noted that charging can be performed wirelessly without the 7206 input / output connector.

[0388] The display section 7202 of the portable information terminal 7200 comprises the secondary battery of an embodiment of the present invention. Using the secondary battery of an embodiment of the present invention allows for the provision of a lightweight portable information terminal with a long service life. For example, the secondary battery 7104, which is located in Fig. 24E is shown and is in the bent state in which housing 7201 is provided. Alternatively, the secondary battery 7104, which is in Fig. 24E is shown in volume 7203 in such a way that it can be bent.

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

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

[0391] The display surface of 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, by short-range communication, which is a communication method based on an existing communication standard.

[0392] The 7300 display unit includes an input / output port, and data can be sent directly to and received from another information terminal via a connecting element. Charging is also possible via the input / output port. It should be noted that charging can be performed wirelessly without using the input / output port.

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

[0394] Additionally, show Fig. 24H, Fig. 25A to 25C and Fig. 26 examples of electrical devices incorporating the secondary battery with excellent cycle characteristics described in the foregoing embodiment.

[0395] If the secondary battery of an embodiment of the present invention is used as the secondary battery of a commonly used electrical device, a lightweight product with a long service life can be provided. Commonly used electrical devices include electric toothbrushes, electric razors, electric beauty equipment, and the like. For ease of handling by users, small, rod-shaped secondary batteries with low weight and high capacity are desirable for these products.

[0396] Fig. 24H is a perspective view of a device called an evaporator. In Fig. The 24H vaporizer 7500 comprises an atomizer 7501 with a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cassette 7502 containing a liquid supply bottle, a sensor, and the like. To improve safety, a protective circuit that prevents overcharging and over-discharging of the secondary battery 7504 can be electrically connected to it. The secondary battery 7504 in Fig. The 24H includes an output port for connecting to a charger. When the vaporizer 7500 is held by a user, the secondary battery 7504 becomes a critical component; therefore, it is preferred that the secondary battery 7504 has a short overall length and is lightweight. With a secondary battery of an embodiment of the present invention that has a high capacity and excellent cycle characteristics, the small and lightweight vaporizer 7500 can be used for extended periods.

[0397] Next, we will... Fig. 25A and Fig. 25B is an example of a foldable tablet computer. A 9600 tablet computer, which is in Fig. 25A and Fig. Figure 25B includes a housing 9630a, a housing 9630b, a movable part 9640 connecting the housings 9630a and 9630b, a display section 9631 comprising a display section 9631a and a display section 9631b, a switch 9626 for switching the display mode, a power switch 9627, a switch 9625 for switching the power-saving mode, a bracket 9629, and an operating switch 9628. A flexible screen is used for the display section 9631, thus providing a tablet computer with a larger display area. Fig. 25A represents the Tablet Computer 9600, which is opened, and Fig. 25B represents the 9600 tablet computer in its closed position.

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

[0399] Part of the display section 9631a can be a touchscreen area 9632a, and data can be entered by touching a displayed control button 9638. Although an example structure is shown 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 can have a touchscreen function. For example, the display section 9631a can display keyboard buttons across its entire area to function as a touchscreen, and the display section 9631b can be used as a display screen.

[0400] Part of display section 9631b, like display section 9631a, can be a touchscreen area 9632b. A control button 9639 for showing / hiding a touchscreen keyboard is touched with a finger, a stylus, or the like, so that keyboard buttons can be displayed on display section 9631b.

[0401] Input by touch can be performed simultaneously in touchscreen areas 9632a and 9632b.

[0402] Switch 9626 for changing display modes allows switching between portrait and landscape orientation, color and black-and-white display, and the like. Switch 9625 for toggling power-saving mode can control the display brightness according to the amount of ambient light measured by an optical sensor in the 9600 tablet computer when the 9600 tablet computer is in use. The tablet computer may have an additional sensing device, such as a tilt sensor (e.g., a gyroscope or accelerometer), in addition to the optical sensor.

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

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

[0405] The 9600 tablet computer can be folded such that the housings 9630a and 9630b overlap when not in use. This protects the display sections 9631a and 9631b, increasing the durability of the 9600 tablet computer. With the energy storage unit 9635, which contains the secondary battery of an embodiment of the present invention and has high capacity and excellent cycle characteristics, the 9600 tablet computer can be used for extended periods.

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

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

[0408] The structure and function of the in Fig. The charging / discharging control circuit 9634 shown in 25B is described with reference to a block diagram in Fig. 25C described. 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 in Fig. 25C is shown, 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 is described in the case where energy is generated by the solar cell 9633 using external light. The voltage of the electrical energy generated by the solar cell is increased or decreased by the DC-DC converter 9636 to a charging voltage for the energy storage unit 9635. When the power from the solar cell 9633 is used to operate the display section 9631, switch SW1 is turned on, and the voltage of the power is increased or decreased by the converter 9637 to a voltage required for the operation of the display section 9631. When no display is running on the display section 9631, switch SW1 is turned off, and switch SW2 is turned on, allowing the energy storage unit 9635 to be charged.

[0410] It should be noted that the solar cell 9633 is described as an example of an energy generation device; however, an embodiment of the present invention is not limited to this example. The energy storage unit 9635 can be charged by means of another energy generation device, such as a piezoelectric element or a thermoelectric converter element (Peltier element). For example, the energy storage unit 9635 can be charged by means of a contactless energy transfer module that wirelessly (contactlessly) transmits and receives energy to charge the battery, or in combination with another charging device.

[0411] Fig. Section 26 presents further examples of electrical appliances. Fig. Figure 26 describes a display device 8000 as an example of an electrical device that includes a secondary battery 8004 of an embodiment of the present invention. In particular, the display device 8000 corresponds to a display device for receiving a television transmission and includes a housing 8001, a display section 8002, speaker sections 8003, the secondary battery 8004, and the like. The secondary battery 8004 of an embodiment of the present invention is provided in the housing 8001. The display device 8000 can receive electrical energy from a commercial power source. Alternatively, the display device 8000 can use electrical energy stored in the secondary battery 8004.Thus, the display device 8000 can be operated as an uninterruptible power source using the secondary battery 8004 of an embodiment of the present invention, even if electrical energy 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 display section 8002.

[0413] It should be noted that, in addition to a device for receiving a television broadcast, the display device in its category includes 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 that uses a secondary battery 8103 of an embodiment of the present invention. In particular, the lighting device 8100 includes a housing 8101, a light source 8102, the secondary battery 8103, and the like. Although Fig. Figure 26 describes the case in which 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 can be provided in the housing 8101. The lighting device 8100 can receive electrical energy from a commercial power source. Alternatively, the lighting device 8100 can use electrical energy stored in the secondary battery 8103. Thus, in an embodiment of the present invention, the lighting device 8100 can be operated as an uninterruptible power source using the secondary battery 8103, even if electrical energy cannot be supplied from a commercial power source due to a power outage or the like.

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

[0416] Light source 8102 can be any artificial light source that artificially emits light by means of energy. In particular, 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 conditioner in Fig. Figure 26, which includes an indoor unit 8200 and an outdoor unit 8204, is an example of an electrical device that includes a secondary battery 8203 of an embodiment of the present invention. In particular, the indoor unit 8200 includes a housing 8201, an air outlet 8202, the secondary battery 8203, and the like. Although Fig. As described in Figure 26, where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 can also be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 can be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive electrical energy from a commercial power source. Alternatively, the air conditioner can use electrical energy 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 as an uninterruptible power source according to an embodiment of the present invention, even if electrical energy cannot be supplied from a commercial power source due to a power outage or the like.

[0418] It should be noted that the split-unit air conditioning system, which includes the indoor unit and the outdoor unit, is one example in Fig. 26 shows that the secondary battery of an embodiment of the present invention can be used in an air conditioning system in which the functions of an indoor unit and an outdoor unit are integrated in one housing.

[0419] A in Fig. Figure 26, the electric freezer-fridge 8300, is an example of an electrical device that includes a secondary battery 8304 of an embodiment of the present invention. In particular, the electric freezer-fridge 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 located in the housing 8301 in Fig. 26. The electric freezer-fridge 8300 can receive electrical energy from a commercial power source. Alternatively, the electric freezer-fridge 8300 can use electrical energy stored in the secondary battery 8304. Thus, using the secondary battery 8304, the electric freezer-fridge 8300 of an embodiment of the present invention can be operated as an uninterruptible power source, even if electrical energy cannot be supplied from a commercial power source due to a power outage or the like.

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

[0421] Additionally, during periods when electrical appliances are not in use, particularly when the ratio of energy actually consumed to the total energy that can be supplied from a commercial power source (referred to as the energy consumption rate) is low, energy can be stored in the secondary battery, thereby reducing the energy consumption rate during periods when the electrical appliances are in use. For example, in the case of the 8300 electric fridge-freezer, energy can be stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and freezer door 8303 are not opened and closed frequently.On the other hand, during the day, 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 can be reduced during the day.

[0422] According to one embodiment of the present invention, the secondary battery can exhibit 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 lighter due to its improved properties. Therefore, the secondary battery of an embodiment of the present invention is used in the electrical device described in that embodiment, resulting in a lighter electrical device with a longer service life. This embodiment can be implemented in suitable combination with any of the other embodiments. (Version 5)

[0423] In this embodiment, examples of vehicles with the secondary battery of an embodiment of the present invention are 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. Figures 27A to 27C each represent an example of a vehicle in which the secondary battery of an embodiment of the present invention is used. A vehicle 8400, which is in Fig. Figure 27A shows an electric vehicle powered by an electric motor. Alternatively, vehicle 8400 is a hybrid electric vehicle that can be operated, as appropriate, either with an electric motor or with an internal combustion engine. One embodiment of the present invention can provide a vehicle with a long mileage. Vehicle 8400 includes the secondary battery. The secondary battery can be the one shown in Fig. 12C and Fig. The modules of the secondary batteries shown in Figure 12D can be arranged such that they are used in a floor section of the motor vehicle. Alternatively, a battery pack containing a plurality of secondary batteries, each in Fig. The components shown in sections 17A to 17C are combined and arranged in a floor section of the vehicle. The secondary battery is used not only to operate an electric motor 8406, but also to supply electrical energy to a light-emitting device, such as a headlight 8401 or interior lighting (not shown).

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

[0427] Fig. 27B represents a vehicle 8500 that includes the secondary battery. The vehicle 8500 can be recharged 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. In 27B, a secondary battery 8024 in the vehicle 8500 is charged by means of a ground-based charger 8021 via a cable 8022. During charging, a suitable method such as CHAdeMO (registered trademark) or Combined Charging System, the standard of a connector, or the like may be used. The ground-based charger 8021 may be a charging station provided in a commercial establishment or a household power source. For example, the secondary battery 8024 in the vehicle 8500 can be charged using a plug-in technology by supplying it with external electrical energy. Charging can be carried out by converting alternating current (AC electric power) into direct current (DC electric power) using a converter, such as an AC-to-DC converter.

[0428] Furthermore, although not shown, the vehicle can include a power receiving device, allowing it to be charged by receiving electrical energy wirelessly from an overhead power transmission device. In the case of a wireless power supply system, the electric vehicle can be charged not only when stationary but also while driving, by installing a power transmission device in a road or exterior wall. Additionally, the wireless power supply system can be used to transfer and receive electrical energy between vehicles. A solar panel can be integrated into the exterior of the vehicle to charge the secondary battery when the vehicle is stationary or moving. To supply electrical energy wirelessly in this way, an electromagnetic induction method or a magnetic resonance method can be used.

[0429] Fig. Figure 27C shows an example of a motorcycle using the secondary battery of an embodiment of the present invention. A motor scooter 8600, which is in Fig. The assembly shown in 27C comprises a secondary battery 8602, side mirrors 8601 and turn signals 8603. The secondary battery 8602 can supply electrical energy to the turn signals 8603.

[0430] Furthermore, in the Fig. In the scooter 8600 shown in Figure 27C, the secondary battery 8602 is stored in a storage unit under the seat 8604. The secondary battery 8602, despite its small size, can be stored in the storage unit under the seat 8604. The secondary battery 8602 is removable; thus, it is moved 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 its capacity can be increased. This allows the secondary battery itself to be made more compact and lighter. The compact and lightweight secondary battery contributes to a reduction in the vehicle's weight, thereby increasing its driving performance. Furthermore, the secondary battery in the vehicle can be used as a power source to supply electrical energy to products other than the vehicle itself. In such a case, for example, it can be avoided to use a commercial power source during peak energy demand. Avoiding the use of a commercial power source during peak energy demand can contribute to energy savings and a reduction in carbon dioxide emissions.Furthermore, the secondary battery can be used for a long period of time if the cycle characteristics are excellent; thus, the amount of rare metals used, such as cobalt, can be reduced.

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

[0433] In this example, the positive electrode active materials, which are embodiments of the present invention, are developed, and the observation results of the positive electrode active materials using STEM, the results of TEM images subjected to a fast Fourier transform, 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, 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.

[0435] In this example, lithium cobalt oxide particles (C-20F, manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD.) were used as the starting material. Therefore, steps 12 and 13 described in embodiment 1 were omitted in this example. It should be noted 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 in 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 to form an isopropanol solution of TTIP. The lithium cobalt oxide particles were then mixed into the solution, resulting in a TTIP-to-magnesium-and-fluorine-containing lithium cobalt oxide ratio of 0.01 ml / g.

[0437] The above-mixed solution was stirred with a magnetic stirrer at 25 °C and a relative humidity of 90% RH for four hours. During the process, water in the 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 preceding process, was filtered to collect the residue. Kiriyama filter paper (No. 4) was used for the filtration.

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

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

[0441] The heated particles were then cooled to room temperature. The cooling time from the retention temperature to room temperature was 10 to 15 hours. Afterwards, a crushing treatment was performed. During the comminution process, the particles were passed through a sieve with an opening size 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 comparison 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 lithium cobalt oxide particles containing magnesium and fluorine were heated. The heating was carried out under the following conditions: The temperature was 800 °C (the 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, as with sample 01, passed through a sieve 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 internally and including an area containing magnesium in a surface section. <<Probe 03> >

[0448] Sample 03 was formed as a comparative example in the following way: A titanium-containing region was formed in the lithium cobalt oxide particles, which did not contain magnesium, by a sol-gel process, 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 percent by XPS.

[0450] A titanium-containing region was formed in the lithium cobalt oxide particles using a sol-gel process, and the lithium cobalt oxide particles were dried, heated, cooled, and sieved as in sample 01. The resulting 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 internally and including an area containing titanium in a surface section. <<Probe 04> >

[0452] For sample 04, lithium cobalt oxide particles were used as a comparison example, without being heated.

[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 a comparison example, without being heated.

[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 T1 enthält, erwärmt Probe 02 LiCoO2+Mg+F, erwärmt Probe 03 LiCoO2, beschichtet mit einem Material, das T1 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 accelerating voltage was 200 kV. Fig. Figure 28 shows the obtained electron microscope image. As in Fig. As shown in Figure 28, the positive electrode active material likely comprises three distinct regions: the first region 101; the second region 102; and the third region 103. The third region 103 is observed to be brighter than the first region 101 and the second region 102. Furthermore, the crystal orientations of the first region 101 and the second region 102 are partially aligned, and the crystal orientations of the second region 102 and the third region 103 are also partially aligned. [STEM-FFT]

[0459] Fig. Figure 29A1 shows an image of a fast Fourier transform (FFT) of a region 103FFT in the STEM image of Fig. 28. In Fig. 29A2 is a midpoint O of Fig. 29A1 is shown by a cross, and bright points A, B, and C are each surrounded by a circle. Similarly, it shows Fig. 29B1 is an FFT image of a 102FFT area. In Fig. 29B2 is a midpoint O of Fig. 29B1 is shown by a cross, and bright points A, B, and C are each surrounded by a circle. Additionally, it shows 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. In 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, 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, region 102FFT likely contains lithium titanate (LiTiO2, cubic crystal).

[0462] In Fig. In 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, region 101FFT likely contains lithium cobaltate (LiCoO2, rhombohedral). [EDX]

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

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

[0465] Next we will show Fig. 31A1, Fig. 31A2, Fig. 31B1, Fig. 31B2, Fig. 31C1 and Fig. 31C2 a HAADF-STEM image and element distribution images with EDX of the positive electrode active material of sample 05, which is a comparison example. Fig. 31A1 shows a HAADF STEM image, Fig. 31A2 shows a distribution image of oxygen atoms, Fig. Figure 31B1 shows a distribution pattern of cobalt atoms. Fig. Figure 31B2 shows a distribution pattern of fluorine atoms. Fig. 31C1 shows a distribution pattern of titanium atoms and Fig. 31C2 shows a distribution pattern of magnesium atoms.

[0466] As in Fig. 31B2 and Fig. As shown in 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 a line analysis using TEM-EDX, which was performed on a cross-section of the environment 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 outer surface of the positive electrode active material of sample 01 to the inner surface of the positive electrode active material. A distance of 0 nm indicates the outer surface of the positive electrode active material, and a distance of 14 nm indicates the interior of the particle. In EDX, the analysis area tends to be large, allowing elements to be detected not only in the center of an electron beam irradiation area but also in a region around the center.

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

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

[0470] From the preceding STEM images, FFT images, elemental distribution images with EDX, and EDX line analysis, it has been determined that sample 01 is a positive electrode active material of an embodiment of the present invention, comprising the first region containing lithium cobaltate, the second region containing lithium, titanium, cobalt, and oxygen, and the third region containing magnesium and oxygen. It has been found that in sample 01, a portion of the second region and a portion of the third region overlap.

[0471] In the graph of Fig. 32 is the amount of oxygen detected at a distance of 4 nm or more, which is stable. Thus, in this example, the average value \O ave the amount of oxygen detected in the stable range is obtained, and it is assumed that a distance x of the measuring point at which the measurement is obtained is 0.5 O ave , i.e., the value of 50% of the average value O ave , is 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 is 674.2. The x-axis of the measurement point where the measurement closest to 337.1, which is 50% of 674.2, is obtained indicates 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 area of ​​the positive electrode active material particle.

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

[0474] The magnesium concentration 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, i.e., to a depth of 2.71 nm from the surface. The measured magnesium concentration is less than 1 / 5 of the peak at a distance of 4.57 nm or more, i.e., at a depth of 2.86 nm or more from the surface of the positive electrode active material particle. Thus, it has been determined that in sample 01, the third region extends from the surface to a depth of 2.71 nm.

[0475] Furthermore, the concentration of titanium is greater than or equal to half the peak from a distance of 2.14 nm to a distance of 3.42 nm. Thus, it has been found that the second region is a range from a depth of 0.43 nm to a depth of 1.71 nm from the surface of the positive electrode active material particle.

[0476] Next, evaluation results of the charging and discharging characteristics of secondary batteries produced using the positive electrode active materials of sample 01 to sample 05, which have been formed in the manner described above, are described. [Production 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, which were formed in the manner described above.

[0478] A positive electrode formed by applying a slurry was used in which a positive electrode active material (LCO), acetylene carbon 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] Lithium hexafluorophosphate (LiPF6) was used as the electrolyte contained in an electrolyte solution, and a solution was used in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 3:7 and vinylene carbonate (VC) at 2 wt%.

[0481] A positive electrode box and a negative electrode box were manufactured from 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, constructed as described above, were evaluated. The measurement temperature was 25 °C. Twenty charge and discharge 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 unit weight of the positive electrode active material.

[0483] Fig. Figure 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 charging and discharging characteristics with a broad plateau. Furthermore, the results of the 20 charging and discharging cycles almost overlap, indicating excellent cycle characteristics.

[0484] Fig. Figure 34 is a graph showing the charging and discharging characteristics of the secondary battery of sample 05, which serves as a comparison example. Excellent charging and discharging characteristics are shown in the initial cycles, as indicated by arrows in Fig. However, as shown in Figure 34, the charging capacity and the discharging capacity decrease with an increase in cycles. [Evaluation of cycle characteristics]<<Aufladen bei 4,4 V> >

[0485] The cycle characteristics of the secondary batteries of sample 01 and sample 05, charged at 4.4 V, were evaluated. The measurement temperature was 25 °C. Charging was performed at 4.4 V (CCCV, 0.5 C, cutoff 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 life of secondary batteries charged at 4.4 V. Fig. Figure 35 shows a solid line and a dashed line indicating secondary batteries containing the positive electrode active materials of sample 01 and sample 05, respectively. As in Fig. Figure 35 shows that the secondary battery containing sample 01 exhibited an energy density retention rate of 99.5% even after 50 charge and discharge cycles, demonstrating excellent cycle 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 cycle characteristics of the secondary batteries of samples 01 to 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, cutoff current of 0.01 C), and discharging was performed at 2.5 V (CC, 0.5 C).

[0488] Fig. Figure 36 is a graph showing the cycle characteristics charged at 4.6 V. As in Fig. Figure 36 shows that the secondary battery containing sample 01, which is the positive electrode active material of an embodiment of the present invention, exhibits an energy density retention rate of 94.1%, even after 50 charge and discharge cycles at a high voltage of 4.6 V, 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; for example, in sample 04, the energy density retention rate was 33.2% after 50 cycles.

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

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

[0491] In this example, a positive electrode active material was formed that 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. [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 carried out 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 titanium oxide-coated, unheated lithium cobalt oxide particles are referred to as sample 06.

[0494] Next, sample 06, consisting of titanium oxide-coated lithium cobalt oxide particles, was heated. Heating was carried out in a muffle furnace in an oxygen atmosphere at 800 °C under the following conditions: the residence time was two hours, and the oxygen flow rate was 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 designated Sample 07. [TEM-EDX]

[0496] Sample 06 and sample 07, in particular cracks created in the particles and the proximity of the cracks, were subjected to analysis using TEM-EDX.

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

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

[0500] As in Fig. 37A, Fig. 37B1, Fig. 37B2, Fig. 37C1, Fig. 37C2, Fig. 37D1, Fig. 37D2, Fig. 37E1 and Fig. 37E2 as well 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 titanium has been segregated on the surface of the crack section by heating.

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

[0502] Fig. 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 that were created with Fig. 37B1, Fig. 37C1, Fig. 37D1 and Fig. 37E1 are identical. Fig. Figure 39B2 shows a Mg distribution pattern of a region that is the same as Fig. 39B1 is. Fig. 39C2 shows a Mg distribution pattern of a region that is the same as Fig. 39C1 is. Fig. Figure 39D2 shows a Mg distribution image of a region that is the same as Fig. 39D1 is. Fig. Figure 39E2 shows a Mg distribution pattern of a region that is the same as Fig. 39E1 is.

[0503] Fig. 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, which are the same as Fig. 38B1, Fig. 38C1, Fig. 38D1 and Fig. 38E1 are. Fig. Figure 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 a region that is the same as Fig. 40C1 is. Fig. 40D2 shows a Mg distribution image of a region 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 as well 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, no magnesium segregation is observed on the particle surfaces or in the crack section before heating. In contrast, in sample 07, magnesium segregation is observed both on the particle surfaces and in the crack section after heating.

[0505] To quantify titanium and magnesium, an EDX point analysis was next performed on the areas affected by the Fig. 37A with 1 to 6 marked circles, and carried out in the areas marked by in Fig. 38A is displayed with 1 to 6 marked circles. Two points were measured in each area.

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

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

[0508] Next we will show Fig. 42A and Fig. 42B Results of EDX point analysis in a magnesium to cobalt atomic ratio. 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 both on the particle surfaces and in the crack section; in contrast, in sample 07 there are many points where the amount of magnesium is increased both on the particle surfaces and in the crack section. Furthermore, the Mg / Co ratio on the particle surfaces ranges between 0.15 and 0.50, and that in the crack section between 0 and 0.22.

[0510] Next, CR2032 type button cell secondary batteries were fabricated using the positive electrode active material from sample 07 after heating. A positive electrode, formed by applying a slurry containing a positive electrode active material (LCO) from sample 02, AB, and polyvinylidene fluoride (PVDF) mixed in a weight ratio of 95:3:2, was used to create a positive electrode current collector. 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 / cm². 2 .

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

[0512] An electrolyte solution was used which was prepared such that 1 mol / l LiPF6 was dissolved in 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 added to the solution at 2 wt%. [Initial properties, rate properties]

[0513] Initial properties and rate properties of the secondary battery using the positive electrode active material of sample 07, which was formed in the above manner, were measured.

[0514] Initial property measurements were performed by charging at CCCV, 0.2 C, 4.6 V, and a cutoff current of 0.05 C, and discharging at CC, 0.2 C, and a cutoff voltage of 3.0 V. Here, 1 C was set to 160 mA / g, which was the current value per unit weight of the positive electrode active material. The measurement temperature was 25 °C. Table 2 shows the initial property measurement results. [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 had been measured. The measurement was performed by varying the discharge rate in the following sequence: 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. It should be noted that, except for the discharge rate, the conditions were the same as those used for the measurement of the initial characteristics. The measurement temperature was 25 °C.

[0516] Table 3 shows the measurement results of the initial properties and the rate properties. Additionally, it shows 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 2,0 207,9 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 used to evaluate rate properties, except that the amount of positive electrode active material layer was 8.2 mg / cm². 2 The temperature characteristics were measured. Charging was performed at 25 °C, CCCV, 0.2 C, 4.6 V, 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 3.0 V. Fig. Figure 44 shows measurement results of temperature characteristics. [Cycle properties]

[0518] Next, a cell was manufactured under conditions similar to those used to measure temperature characteristics, and its cycle characteristics were measured. For the cycle characteristics measurement, 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 measurement temperature for the cycle characteristics was 45°C, and 100 cycles were recorded. 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 area of ​​the positive electrode active material of sample 07 was 0.13 m². 2 / G.

[0520] 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 furthermore 21.5 µm, 10 %D was 13.1 µm, 50 %D was 22.0 µm and 90 %D was 34.4 µm.

[0521] The tapping density of the positive electrode active material of sample 07 is 2.21 g / cm³. 3 The knock density was measured using the 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 that a side reaction will be inhibited. Furthermore, even at a high discharge rate of 2 C, an excellent capacity of 96.1% is shown using 0.2 C as a reference. [Example 3]

[0523] In this example, a positive electrode active material comprising an area containing titanium and magnesium in a surface section 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 procedures and conditions for these samples are as follows. <<Proben 11 bis 17> >

[0525] First, a lithium source, a cobalt source, a magnesium source, and a fluorine source, intended 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 for sample 11 were weighed such that the Li to Co ratio was 1.00. The starting materials for sample 12 were weighed such that the Li to Co ratio was 1.03. The starting materials for sample 13 were weighed such that the Li to Co ratio was 1.05. The starting materials for sample 14 were weighed such that the Li to Co ratio was 1.06. The starting materials for sample 15 were weighed such that the Li to Co ratio was 1.07. The starting materials for sample 16 were weighed such that the Li to Co ratio was 1.08. The starting materials for sample 17 were weighed such that the Li to Co ratio was 1.13.

[0527] Furthermore, the starting materials of each of the 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 for 10 hours at 1000 °C under the following conditions: the temperature rise rate was 200 °C / h; and the dry air flow rate was 10 l / min.

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

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

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

[0533] The mixed solution described above was stirred with a magnetic stirrer for four hours at 25 °C and a relative humidity of 90%. During the process, water in the 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 preceding process, was filtered to collect the residue. Kiriyama filter paper (No. 4) was used for the filtration.

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

[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 process. During this process, the particles were passed through a sieve with an opening of 53 µm.

[0538] The particles that had undergone comminution were used as positive electrode active materials for samples 11 to 17. <<Proben 21 bis 27> >

[0539] The starting materials for samples 21 to 27 were the same as those for samples 11 to 16. At this time, the starting materials for sample 21 were weighed such that the Li to Co ratio was 1.00. The starting materials for sample 22 were weighed such that the Li to Co ratio was 1.03. The starting materials for sample 23 were weighed such that the Li to Co ratio was 1.05. The starting materials for sample 24 were weighed such that the Li to Co ratio was 1.06. The starting materials for sample 25 were weighed such that the Li to Co ratio was 1.07. The starting materials for sample 26 were weighed such that the Li to Co ratio was 1.08. The starting materials for sample 27 were weighed such that the Li to Co ratio 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 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 in sample 28 were equal to the ratio of Li to Co of the starting materials and the amount of TTIP in 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, baking was carried out at 950 °C after mixing the starting materials.

[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 internally and a surface section containing titanium and magnesium. <<Proben 31 bis 40> >

[0545] Samples 31 to 40 were formed as comparison examples, none of which contained an area containing titanium.

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

[0547] In addition, the starting materials of each of the samples 31 to 40 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.

[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 for 10 hours at 1000 °C under the following conditions: the temperature rise rate was 200 °C / h; and the dry air flow rate was 10 l / min.

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

[0551] The synthesized particles were cooled and then 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.

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

[0553] The particles that had undergone comminution were used as positive electrode active materials for 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 1000 °C Sample 12 1,03 Sample 13 1,05 Sample 14 1,06 0.01 ml / g Sample 15 1,07 Sample 16 1,08 Sample 17 1,13 Sample 21 1,00 1000 °C Sample 22 1,03 Sample 23 1,05 Sample 24 1,06 0.02 ml / g 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 results of the XPS analysis of samples 11 to 17, Table 6 shows the results of the XPS analysis of samples 21 to 28, and Table 7 shows the results of the XPS analysis of samples 31 to 40. Tables 5 to 7 show the relative concentration of each element, assuming a cobalt concentration of 1. [Table 7] relative value under the condition that the concentration of CO 1 is Li / Co Li Co O C F Mg Approx 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 in Tables 5 to 7. Fig. 46A is a graph showing the ratio of Li to Co and the relative value of magnesium. Fig. 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 present, the concentration of magnesium 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 due to the magnesium present in the starting materials being segregated by heating in a range where the elemental concentration can be detected by XPS. In contrast, the concentration of magnesium is low in samples where the Li to Co ratio is greater than or equal to 1.06; it is therefore likely that magnesium segregation does not occur readily when the amount of lithium is too high.

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

[0559] Furthermore, in the case where the Li to Co ratio is 1.06, the magnesium concentration in the range where elemental concentration can be detected by XPS is low in samples lacking the titanium-containing region; conversely, in samples containing the titanium-containing region, the magnesium concentration in the range where elemental concentration can be detected by XPS is high. This means that if the titanium-containing region forms in the surface area, magnesium is sufficiently segregated even if the Li to Co ratio is high.

[0560] It should be noted that even if the titanium-containing area is included, the magnesium concentration is lower when the Li to Co ratio is 1.07 than when the Li to Co ratio is 1.06. Furthermore, it is likely that when the Li to Co ratio is greater than or equal to 1.08, magnesium segregation will not occur readily, even if the titanium-containing area is included. [Evaluation of cycle characteristics]< <energiedichte-retentionsrate>>

[0561] Next, the cycle properties were evaluated in a similar manner to 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 the 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 external part, the conditions of the cycle property test 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 designed such that the amount of TTIP per weight of positive electrode active material was 0.01 ml / g. Fig. Figure 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 designed such that the amount of TTIP per weight of 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 ratio of Li to Co is greater than or equal to 1.00 and less than or equal to 1.06, exhibit excellent cycling properties. In particular, samples 11 and 12, i.e., the positive electrode active materials in which the ratio of Li to Co is greater than or equal to 1.00 and less than or equal to 1.03, exhibit very excellent cycling properties. In contrast, in sample 16, where the ratio of Li to Co 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 ratio of Li to Co is greater than or equal to 1.00 and less than or equal to 1.06, exhibit excellent cycling properties. Samples 23 and 24, i.e., the positive electrode active materials in which the ratio of Li to Co is particularly greater than or equal to 1.05 and less than or equal to 1.06, exhibit extremely excellent cycling properties.

[0566] Fig. Figure 48 is a graph showing a comparison between sample 11 with the best cycle properties among samples 11 to 15 and sample 23 with the best cycle properties among samples 21 to 25.

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

[0568] Next, we will show Fig. 49 Evaluation results of a discharge capacity retention rate, which is one of the cycle properties of each of the 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 external part, the conditions of the cycle property test and the like of samples 21 to 26 are the same as those in Example 1.

[0570] The secondary battery using sample 28 was prepared in a similar manner to the secondary batteries using samples 21 to 26, except that PVDF was used as the 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 cycle characteristics. In particular, sample 28 exhibits excellent cycle 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 ratios of Li to Co are 1.07 and 1.08 respectively, the discharge capacity retention rates decrease at a relatively early time.

[0573] From the foregoing results, it has been found that when TTIP is 0.02 ml / g per weight of positive electrode active material, the Li to Co ratio preferably has a range greater than or equal to 1.00 and less than 1.07. Furthermore, it has been found that a sample in which the Li to Co ratio has a range greater than or equal to 1.05 and less than or equal to 1.06 exhibits very excellent cycle properties.

[0574] Fig. 50A to 50C show charging and discharging curves of the secondary batteries using probe 28, which is in Fig. 49 exhibits very excellent cycle properties, as do sample 24 and sample 25, where degradation occurs at a relatively early stage.

[0575] Fig. 50A, Fig. 50B and Fig. Figure 50C shows 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 from 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 an embodiment of the present invention, exhibit a high charge and discharge capacity and excellent charge and discharge characteristics. Furthermore, it has been found that a decrease in the charge and discharge capacity of each of sample 28 and sample 24 in Fig. 50A and Fig. 50B compared to sample 25 in Fig. 50°C is significantly suppressed. [Example 4]

[0577] This example describes SEM observation results and SEM-EDX analysis results of the positive electrode active material of sample 24 formed in Example 2.

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

[0579] As in Fig. As shown in Figures 51A to 51C, there is a large number of projected areas in a surface section of the positive electrode active material.

[0580] Next we will show 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 a SEM image of a surface section 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 A region where the number of elements is less than or equal to a lower measurement limit is displayed in black, and when the number of elements is increased, the black region 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 projected areas in the surface section of the positive electrode active material.

[0582] Thus, it has been found that sample 24 is a positive electrode active material containing the aforementioned fourth region 104, which contains titanium and magnesium, above the third region 103.

[0583] As shown in Example 2, sample 24 is one of the samples that exhibits very excellent cycle properties. Thus, it has been found that the positive electrode active material with excellent cycle properties can be obtained even if the fourth region is provided in the surface section.

[0584] From the results of Examples 1 to 3 above, it is evident that if the titanium-containing region is formed in the surface section, the positive electrode active material can be obtained with excellent cycling properties. Furthermore, it has been found that increasing the Li to Co ratio to increase the particle diameter of the positive electrode active material could deteriorate the cycling properties; however, since the titanium-containing region is formed in the surface section, the range of Li to Co ratios in which excellent cycling properties are obtained can be extended. It has also been found that even if the fourth region, containing titanium and magnesium, is located in the surface section of the positive electrode active material, excellent cycling properties are obtained. [Example 5]

[0585] This example presents a method for producing a graphene oxide-coated positive electrode active material and describes observational results of the positive electrode active material produced by the method using an electron microscope.

[0586] As in a process flow diagram in Fig. As shown in Figure 53, a process for forming a coating film on a positive electrode active material comprises 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] It should be noted that in (S12) pure water is used as the dispersion medium; however, the dispersion medium is not particularly restricted and ethanol or the like may be used. Additionally, in (S14) the active material is a positive electrode active material.

[0588] Fig. Figure 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 fed to the nozzle 282 through a tube 283. The suspension 284 is fed into the chamber 281 from the nozzle 282 in the form of a mist and is dried in the chamber 281. The nozzle 282 can be heated by a heater 285. This heats an area of ​​the chamber 281 that is close to the nozzle 282, for example, an area defined by the double-dashed line in Figure 54. Fig. 54 is surrounded, also heated by the heating system 285.

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

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

[0591] An example of the conditions for the formation of 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 the lithium or damaging the active material and thus altering its surface structure. Therefore, the graphene oxide was dispersed in a solution with a 4:6 ratio of ethanol to pure water.

[0594] Stirring to disperse the graphene oxide in a solution was carried out under the following conditions: A stirrer and an ultrasonic wave generator were used; a rotation rate was 750 rpm; and the irradiation time with ultrasonic waves 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 irradiation time of 1 minute. The suspension was prepared by the above procedure. The 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 evenly sprayed using a spray nozzle (with a nozzle diameter of 20 µm) of the spray drying device to obtain a powder. The hot air temperature of the spray drying device was 160 °C inlet temperature and 40 °C outlet temperature, and the N₂ gas flow rate was 10 l / min.

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

[0599] It has been found that the coating film is applied more evenly to the surface of the powder compared to 57 others. Fig. 56 is trained.

[0600] Fig. 58A and Fig. 58B represents 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. Figure 58A is a longitudinal section view of the active material layer 200. The active material layer 200 comprises positive electrode active material particles 100 coated with graphene oxide, a graphene compound 201 as a conductive additive, and a binder (not shown). For example, graphene or multilayer graphene can be used as the graphene compound 201. The graphene compound 201 preferably has a sheet-like shape. The graphene compound 201 can have a film-like shape formed from several layers of multilayer graphene and / or several layers of graphene that partially overlap.

[0602] In the longitudinal section of the active material layer 200, as shown in Fig. Figure 58B shows the positive electrode active material 100 coated with a coating film 105 formed from graphene oxide in contact with the graphene compound 201. A plurality of graphene compounds 201 are formed such that they are partially in contact with 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 conduction path can be formed.

[0604] The coating film 105 is effective in protecting the crystal structure of the positive electrode active material 100, so that it does not come into contact with the electrolyte solution, and in forming the excellent conduction path. Reference sign 11a Positive electrode, 11b Negative electrode, 12a line, 12b Line, 14 Separator, 15a Connecting section, 15b Connecting section, 17 Fastening element, 50 Secondary battery, 51 Exterior part, 61 bending section, 62 Sealing section, 63 Sealing section, 71 Ridge line, 72 Valley line, Room 73 100 positive electrode active material, Area 101, 101p crystal plane, Area 102, 102p crystal plane, Area 103, 103p crystal plane, Area 104, 105 coating film, 106 Crack section, 110 particles, Area 111, 112th layer, 114 Cobalt oxide layer, 120 particles, Area 121, 122 layers, 124 Cobalt oxide layer, 125 layers, 200 active material layer, 201 graphene connection, 214 Separator, 280 Spray drying device, 281 Chamber, 282 nozzle, 283 pipe, 284 Suspension, 285 Heating, 286 collection containers, 288 Arrow, 300 Secondary battery, 301 positive electrode dose, 302 Negative electrode box, 303 Seal, 304 Positive electrode, 305 Positive electrode current collector, 306 Positive electrode active material layer, 307 Negative electrode, 308 Negative electrode current collector, 309 Negative electrode active material layer, 310 Separator, 500 secondary battery, 501 Positive electrode current collector, 502 Positive electrode active material layer, 503 Positive electrode, 504 Negative electrode current collector, 505 Negative electrode active material layer, 506 Negative electrode, 507 Separator, 508 Electrolyte solution, 509 Exterior part, 510 Positive electrode connection electrode, 511 Negative electrode connection electrode, 600 Secondary battery, 601 Positive electrode cap, 602 Battery box, 603 Positive electrode connection, 604 Positive electrode, 605 Separator, 606 Negative electrode, 607 Negative electrode connection, 608 Insulating board, 609 Insulating board, 611 PTC element, 612 Safety valve mechanism, 613 conductive plate, 614 conductive plate, 615 module, 616 Line, 617 Temperature control device, 900 circuit boards, 910 label, 911 connection, 912 circuit, 913 Secondary battery, 914 Antenna, 915 antenna, 916th shift, 917th shift, 918 Antenna, 920 Display device, 921 Sensor, 922 connection, 930 cases, 930a housing, 930b housing, 931 Negative electrode, 932 Positive electrode, 933 Separator, 950 wound part, 951 connection, 952 connection, 980 Secondary battery, 981 Film, 982 Film, 993 wound part, 994 Negative electrode, 995 Positive electrode, 996 Separator, 997 Connection electrode, 998 Connection electrode, 7100 portable display device, 7101 Housing, 7102 Display section, 7103 Control knob, 7104 Secondary battery, 7200 portable information terminal, 7201 Enclosure, 7202 Display section, Volume 7203, 7204 Buckle, 7205 Control knob, 7206 Input / Output Port, 7207 Icon, 7300 Display device, 7304 Display section, 7400 mobile phone, 7401 Housing, 7402 Display section, 7403 Control knob, 7404 external connection port, 7405 loudspeaker, 7406 microphone, 7407 Secondary battery, 7408 Connection electrode, 7409 power collector, 7500 evaporators, 7501 Atomizer, 7502 cassette, 7504 Secondary battery, 8000 Display device, 8001 Enclosure, 8002 Display section, 8003 Loudspeaker section, 8004 Secondary battery, 8021 charger, 8022 cable, 8024 Secondary battery, 8100 Lighting equipment, 8101 Housing, 8102 Light source, 8103 Secondary battery, 8104 Ceiling, 8105 Wall, 8106 Boden, 8107 windows, 8200 Indoor unit, 8201 Housing, 8202 Air outlet, 8203 Secondary battery, 8204 Outdoor unit, 8300 electric fridge-freezer, 8301 Housing, 8302 Refrigerator door, 8303 Freezer door, 8304 Secondary battery, 8400 vehicle, 8401 Headlights, 8406 Electric motor, 8500 vehicles, 8600 scooters, 8601 Side mirrors, 8602 Secondary battery, 8603 Turn signal, 8604 Storage unit under one seat, 9600 tablet computers, 9625 switch, 9626 switches, 9627 Power switch, 9628 Control switch, 9629 bracket, 9630 Housing, 9630a housing, 9630b housing, 9631 Display section, 9631a Display section, 9631b Display section, 9632a area, 9632b area, 9633 Solar cell, 9634 Charging / discharging control circuit, 9635 Energy storage unit, 9636 DC-DC converter, 9637 converter, 9638 Control button, 9639 button, 9640 moving part. < / negativelektrodenstromkollektor> < / negativelektrodenaktivmaterial> < / positivelektrodenstromkollektor> < / positivelektrodenaktivmaterialschicht>

Claims

[1] Method for manufacturing a lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises a positive electrode, a negative electrode and an electrolyte solution, wherein the positive electrode contains a positive electrode active material, wherein the positive electrode active material comprises a positive electrode active material particle, and wherein the method comprises the following steps: Coating a composite oxide with a titanium-containing material, wherein the composite oxide contains lithium, cobalt, magnesium, and fluorine; and Heating the composite oxide at a temperature of 500 °C or higher and 1200 °C or lower, wherein the heating step segregates titanium, magnesium and fluorine in a crack section of the positive electrode active material particle, wherein magnesium and fluorine are segregated in a surface section of the positive electrode active material particle, and wherein titanium diffuses into the interior of the positive electrode active material particle. [2] Method for manufacturing a lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises a positive electrode, a negative electrode and an electrolyte solution, wherein the positive electrode contains a positive electrode active material, wherein the positive electrode active material comprises a positive electrode active material particle, and wherein the method comprises the following steps: Coating a composite oxide with a titanium-containing material, wherein the composite oxide contains lithium, cobalt, magnesium, and fluorine; and Heating the composite oxide at a temperature of 500 °C or higher and 1200 °C or lower, wherein, through the heating step, titanium, magnesium and fluorine are segregated in a crystal defect of the positive electrode active material particle, wherein magnesium and fluorine are segregated in a surface section of the positive electrode active material particle, and wherein titanium diffuses into the interior of the positive electrode active material particle. [3] Method for producing a lithium-ion secondary battery according to claim 1 or 2, wherein the heating step is carried out at a temperature of 800 °C or higher and 1000 °C or lower. [4] Method for producing a lithium-ion secondary battery according to claim 1 or 2, wherein the heating step is carried out in an oxygen-containing atmosphere. [5] Method for producing a lithium-ion secondary battery according to claim 1 or 2, wherein the step of coating with the titanium-containing material is carried out by a sol-gel process. [6] Method for producing a lithium-ion secondary battery according to claim 1 or 2, wherein a distribution of magnesium and a distribution of titanium overlap during the heating step. [7] Method for producing a lithium-ion secondary battery according to claim 1 or 2, wherein a distribution of magnesium and a distribution of titanium overlap during the heating step in a line analysis of energy-dispersive X-ray spectrometry.

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