Method for manufacturing lithium-ion secondary battery

Abstract

A manufacturing method of a lithium ion secondary battery is provided. A positive electrode active material having a layered rock salt type crystal structure, such as lithium cobaltate, is provided with two regions on the surface thereof, wherein the inner region is a non-stoichiometric compound containing a transition metal such as titanium, and the outer region is a compound of a main group element such as magnesium oxide. Each of the two regions has a rock salt type crystal structure. The layered rock salt type crystal structure of the inner region and the two regions of the surface layer portion are topologically derived, whereby changes in the crystal structure of the positive electrode active material due to charging and discharging can be effectively suppressed. Furthermore, because the outer coating layer in contact with the electrolyte uses a compound of a main group element that is chemically stable, a secondary battery with superior cycle characteristics can be provided.

Description

[0001] This invention application is a divisional application of the invention patent application with international application number PCT / IB2017 / 053896, international application date of June 29, 2017, and Chinese national phase application number 201780039613.8, entitled "Positive electrode active material, method for manufacturing positive electrode active material and secondary battery". Technical Field

[0002] One embodiment of the present invention relates to an article, method, or manufacturing method. The present invention relates to a process, machine, product, or composition. One embodiment of the present invention relates to a semiconductor device, display device, light-emitting device, energy storage device, lighting device, electronic device, or a method of manufacturing the same. In particular, one embodiment of the present invention relates to a positive electrode active material for use in secondary batteries, a secondary battery, and electronic devices including a secondary battery.

[0003] In this specification, the term "energy storage device" refers to all components and devices with energy storage function. For example, batteries such as lithium-ion secondary batteries (also known as rechargeable batteries), lithium-ion capacitors, and double-layer capacitors are all included in the scope of energy storage devices.

[0004] In this specification, electronic equipment refers to all devices with energy storage devices, such as electro-optical devices with energy storage devices and information terminal devices with energy storage devices. Background Technology

[0005] In recent years, the development of various energy storage devices, such as lithium-ion rechargeable batteries, lithium-ion capacitors, and air batteries, has been very active. In particular, with the development of the semiconductor industry for portable information terminals such as mobile phones, smartphones, tablets, and laptop computers, portable music players, digital cameras, medical devices, and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), or plug-in hybrid electric vehicles (PHEVs), the demand for high-output, high-energy-density lithium-ion rechargeable batteries has surged. As a rechargeable energy source, they have become a necessity in modern information society.

[0006] The characteristics currently required for lithium-ion rechargeable batteries include: higher energy density, improved cycle performance, and enhanced safety and long-term reliability under various operating environments.

[0007] Therefore, research is underway to improve the positive electrode active material in order to enhance the cycle characteristics and capacity of lithium-ion secondary batteries (Patent Document 1 and Patent Document 2).

[0008] [References]

[0009] [Patent Literature]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2012-018914

[0011] [Patent Document 2] Japanese Patent Application Publication No. 2015-201432 Summary of the Invention

[0012] There is room for improvement in the research and development of lithium-ion secondary batteries and the positive electrode active materials used in them, in terms of charge-discharge characteristics, cycle characteristics, reliability, safety, or cost.

[0013] One objective of one embodiment of the present invention is to provide a positive electrode active material that suppresses capacity reduction during charge-discharge cycles when used in a lithium-ion secondary battery. Furthermore, one objective of one embodiment of the present invention is to provide a high-capacity secondary battery. Additionally, one objective of one embodiment of the present invention is to provide a secondary battery with excellent charge-discharge characteristics. Furthermore, one objective of one embodiment of the present invention is to provide a secondary battery with high safety or reliability.

[0014] Furthermore, one objective of one embodiment of the present invention is to provide a novel substance, active material particles, secondary battery, or method of manufacturing the same.

[0015] Note that the description of these objectives does not preclude the existence of other objectives. One embodiment of the invention does not need to achieve all of the above objectives. Furthermore, objectives other than those described above can be extracted from the description, drawings, and claims.

[0016] To achieve the above objectives, in one embodiment of the present invention, two regions different from the internal region of the positive electrode active material are provided on the surface layer. The inner region preferably contains a non-uniform compound, while the outer region preferably contains a uniform compound.

[0017] Furthermore, the inner region preferably contains titanium, while the outer region preferably contains magnesium. Moreover, these two regions can overlap.

[0018] Furthermore, the inner region is preferably formed by a coating method such as the sol-gel method, while the outer region is preferably formed by segregation accompanied by heating.

[0019] 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 on the surface of the positive electrode active material. The third region is located closer to the surface of the positive electrode active material than the second region. The first region comprises an oxide of lithium and a first transition metal and has a layered rock-salt type crystal structure. The second region comprises an integrity compound having an oxide of a second transition metal, the integrity compound having a rock-salt type crystal structure. The third region comprises a compound having a main group element, the main group element compound having a rock-salt type crystal structure.

[0020] In the above structure, the first transition metal is preferably cobalt, the second transition metal is preferably titanium, and the compound of the main group element is preferably magnesium oxide.

[0021] In the above structure, the third region may also contain fluorine. Furthermore, both the second and third regions may contain cobalt.

[0022] In the above structure, the crystal orientation of the first region is preferably consistent with the crystal orientation of the second region, and the crystal orientation of the second region is preferably consistent with the crystal orientation of the third region.

[0023] In the above structure, the mismatch between the (1-1-4) plane or the plane orthogonal to the (1-1-4) plane of the layered rock salt crystal structure in the first region and the {100} plane of the rock salt crystal structure in the second region is preferably less than 0.12, and the mismatch between the {100} plane of the rock salt crystal structure in the second region and the {100} plane of the rock salt crystal structure in the third region is preferably less than 0.12.

[0024] Another embodiment of the present invention is a positive electrode active material comprising lithium, titanium, cobalt, magnesium, oxygen, and fluorine. When the concentration of cobalt present in the surface portion of the positive electrode active material, as measured by X-ray photoelectron spectroscopy, is 1, the concentration of titanium is 0.05 or more and 0.4 or less, the concentration of magnesium is 0.4 or more and 1.5 or less, and the concentration of fluorine is 0.05 or more and 1.5 or less.

[0025] 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, cobalt source, magnesium source, and fluorine source at a temperature of 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 a titanium alkoxide in an alcohol; a step of mixing the particles containing lithium, cobalt, magnesium, oxygen, and fluorine in an alcohol solution of the titanium alkoxide and stirring in an atmosphere containing water vapor; a step of collecting a deposit from the mixture; and a step of heating the collected deposit in an atmosphere containing oxygen at a temperature of 500°C or higher and 1200°C or lower for 50 hours or less.

[0026] In the above formation 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 1.00 ≤ Li / Co < 1.07.

[0027] In the above formation method, the preferred ratio of the number of magnesium atoms in the magnesium source to the number of fluorine atoms in the fluorine source is Mg:F = 1:x (1.5 ≤ x ≤ 4).

[0028] In the above-described formation method, the number of magnesium atoms in the magnesium source is preferably 0.5 at% or more and 1.5 at% or less than the number of cobalt atoms in the cobalt source.

[0029] In the above-mentioned formation method, lithium carbonate, cobalt oxide, magnesium oxide and lithium fluoride can be used as lithium source, cobalt source, magnesium source and fluorine source respectively.

[0030] By using a coating film to cover the surface of the positive electrode active material to protect the crystal structure, the capacity reduction accompanying charge-discharge cycles can be suppressed. As the coating film covering the surface of the positive electrode active material, a coating film containing carbon (a film containing a graphene compound) or a coating film containing lithium or electrolyte decomposition products can be used.

[0031] In particular, it is preferable to use a spray drying device to obtain powder in which the surface of the positive electrode active material is coated with graphene oxide. A spray drying device is a manufacturing apparatus that utilizes a spray drying method to remove the dispersion medium by supplying hot air to the suspension.

[0032] Repeated charge-discharge cycles can cause deformation of the positive electrode active material particles, such as cracking or splitting. This deformation exposes new surfaces of the positive electrode active material, which come into contact with the electrolyte and cause decomposition reactions, thus degrading the cycle characteristics and charge-discharge characteristics of the secondary battery.

[0033] Therefore, it is preferable to provide a coating membrane to prevent deformation of the positive electrode active material particles, such as cracking or splitting.

[0034] However, when a suspension is formed and stirred using a rotary mixer to coat the surface of a heavy positive electrode active material per unit volume with relatively light graphene oxide per unit volume, the coating is insufficient.

[0035] Therefore, in order to use graphene oxide to coat the surface of the positive electrode active material particles, the following method is preferred: mixing graphene oxide and a polar solvent (water, etc.) and subjecting the mixture to ultrasonic treatment to prepare a suspension of the mixed positive electrode active material particles, followed by using a spray drying device to generate a dried powder. The dried powder thus generated is sometimes referred to as a composite.

[0036] The size of a drop of liquid sprayed from a spray drying device depends on the nozzle diameter.

[0037] When the particle size is smaller than the nozzle diameter, multiple particles exist within a single drop of the spray liquid ejected from the nozzle. When observing the surface of the dried particles under the condition that the maximum particle size is smaller than the nozzle diameter, it was confirmed that the surface is coated with graphene oxide, but the coating is not yet sufficient.

[0038] The nozzle diameter of the spray drying equipment is preferably substantially equal to the maximum particle size of the positive electrode active material, as this improves the coverage of the active material. Furthermore, when forming the positive electrode active material, it is preferable to adjust the maximum particle size of the positive electrode active material to be substantially equal to the nozzle diameter.

[0039] Because graphene oxide is easily dispersed in water, a suspension of water and graphene oxide can be formed by stirring with ultrasound. A positive electrode active material is then added to this suspension and sprayed using a spray dryer, thereby obtaining a powder with the surface of the positive electrode active material coated with graphene oxide.

[0040] The higher the amount of graphene oxide, the more acidic the suspension. This can potentially lead to etching of a portion of the surface of the positive electrode active material (e.g., LiCoO2 containing Mg or F). Therefore, it is preferable to adjust the hydrogen ion index (pH) of the suspension before spraying to approximately pH 7, i.e., near neutral, or pH 8 or higher, i.e., alkaline. For this pH adjustment, an aqueous solution of LiOH is preferred. For example, when using LiCoO2 as the positive electrode active material and using only pure water as the dispersion medium of the suspension, the surface of the positive electrode active material can sometimes be damaged. Therefore, by using a mixture of ethanol and water as the dispersion medium of the suspension, damage to the surface of the active material can be reduced.

[0041] By forming a suspension using the above method, positive electrode active materials with graphene oxide coatings on their surfaces can be prepared efficiently. This graphene oxide coating prevents deformation of the positive electrode active material particles, such as cracking or splitting. Furthermore, the graphene oxide-coated positive electrode active material can resist deterioration or degradation even after exposure to the atmosphere. Here, "after formation" refers to the period from the completion of positive electrode active material formation to the start of secondary battery formation containing the positive electrode active material, including storage and transportation of the positive electrode active material. Moreover, by forming a coating film, direct contact between the positive electrode active material and the electrolyte can be prevented from causing a reaction, thereby providing high reliability for secondary batteries using this coating film.

[0042] As a spray drying method, known equipment can be used, such as countercurrent pressurized nozzle spray drying equipment or countercurrent pressurized nozzle spray drying equipment.

[0043] When used in secondary batteries, the graphene oxide covering the surface of the active material can also be reduced. This reduced graphene oxide is sometimes referred to as "RGO (Reduced Graphene Oxide)". Sometimes in RGO, some oxygen atoms remain as oxygen atoms bonded to carbon or as oxygen-containing groups. For example, RGO may contain functional groups such as epoxy groups, carbonyl groups such as carboxyl groups, or hydroxyl groups.

[0044] Another embodiment of the present invention is a secondary battery comprising a positive electrode and a negative electrode containing the above-mentioned positive electrode active material or the above-mentioned positive electrode active material covered by a coating film.

[0045] Secondary batteries can have various shapes to fit the device in which they are used, such as cylindrical, angular, coin-shaped, and flat (flat) shapes.

[0046] According to one embodiment of the present invention, a positive electrode active material can be provided that suppresses capacity reduction during charge-discharge cycles when used in a lithium-ion secondary battery. Furthermore, a secondary battery with excellent charge-discharge characteristics can be provided. Furthermore, a secondary battery with high safety or reliability can be provided. Additionally, novel materials, active material particles, secondary batteries, or methods for forming the same can be provided. Attached Figure Description

[0047] In the attached diagram:

[0048] Figures 1A to 1C This is a diagram illustrating an example of a positive electrode active material;

[0049] Figure 2A and Figure 2B It is a diagram illustrating the crystal structure of the positive electrode active material;

[0050] Figure 3 It is a diagram illustrating the crystal structure of the positive electrode active material;

[0051] Figure 4A-1 , Figure 4A-2 , Figure 4A-3 , Figure 4B , Figure 4C , Figure 4D-1 as well as Figure 4D-2 This is a diagram illustrating the sol-gel method;

[0052] Figures 5A to 5C It is a diagram illustrating the segregation model of elements contained in the positive electrode active material;

[0053] Figures 6A to 6D It is a diagram illustrating the segregation model of elements contained in the positive electrode active material;

[0054] Figure 7A and Figure 7B It is a cross-sectional view of the active material layer containing graphene compounds as a conductive additive;

[0055] Figures 8A to 8C This is a diagram illustrating the charging method for secondary batteries;

[0056] Figures 9A to 9D This is a diagram illustrating the charging method for secondary batteries;

[0057] Figure 10 This is a diagram illustrating the discharge method of a secondary battery;

[0058] Figures 11A to 11C This is a diagram illustrating a coin-type secondary battery;

[0059] Figures 12A to 12D This is a diagram illustrating a cylindrical secondary battery;

[0060] Figure 13A and Figure 13B This is a diagram illustrating an example of a secondary battery;

[0061] Figure 14A-1 , Figure 14A-2 , Figure 14B-1 as well as Figure 14B-2 This is a diagram illustrating an example of a secondary battery;

[0062] Figure 15A and Figure 15B This is a diagram illustrating an example of a secondary battery;

[0063] Figure 16 This is a diagram illustrating an example of a secondary battery;

[0064] Figures 17A to 17C This is a diagram illustrating a laminated secondary battery;

[0065] Figure 18A and Figure 18B This is a diagram illustrating a laminated secondary battery;

[0066] Figure 19 This is a diagram showing the appearance of a secondary battery;

[0067] Figure 20 This is a diagram showing the appearance of a secondary battery;

[0068] Figures 21A to 21C This is a diagram illustrating a method for forming a secondary battery;

[0069] Figure 22A , Figure 22B1 , Figure 22B2 , Figure 22C as well as Figure 22D This is a diagram illustrating a flexible secondary battery;

[0070] Figure 23A and Figure 23B This is a diagram illustrating a flexible secondary battery;

[0071] Figures 24A to 24H This is a diagram illustrating an example of an electronic device;

[0072] Figures 25A to 25C This is a diagram illustrating an example of an electronic device;

[0073] Figure 26 This is a diagram illustrating an example of an electronic device;

[0074] Figures 27A to 27C This is a diagram illustrating an example of an electronic device;

[0075] Figure 28 This is a transmission electron microscope image of the positive electrode active material of Example 1;

[0076] Figure 29A1 , Figure 29A2 , Figure 29B1 , Figure 29B2 , Figure 29C1 as well as Figure 29C2 This is an FFT image of the transmission electron microscope image of the positive electrode active material in Example 1;

[0077] Figure 30A1 , Figure 30A2 , Figure 30B1 , Figure 30B2 , Figure 30C1 as well as Figure 30C2 This is the elemental distribution diagram of the positive electrode active material in Example 1;

[0078] Figure 31A1 , Figure 31A2 , Figure 31B1 , Figure 31B2 , Figure 31C1 as well as Figure 31C2 This is an elemental distribution diagram of the positive electrode active material in the comparative example of Example 1;

[0079] Figure 32 This is a graph showing the TEM-EDX line analysis results of the positive electrode active material of Example 1;

[0080] Figure 33 This is a graph showing the charge and discharge characteristics of the secondary battery of Example 1;

[0081] Figure 34 This is a graph showing the charge-discharge characteristics of the secondary battery of the comparative example of Example 1;

[0082] Figure 35 This is a graph showing the cycle characteristics of the secondary battery of Example 1;

[0083] Figure 36 This is a graph showing the cycle characteristics of the secondary battery of Example 1;

[0084] Figure 37A , Figure 37B1 , Figure 37B2 , Figure 37C1 , Figure 37C2 , Figure 37D1 , Figure 37D2 , Figure 37E1 as well as Figure 37E2 These are TEM-EDX surface analysis images of a comparative example from Example 2;

[0085] Figure 38A , Figure 38B1 , Figure 38B2 , Figure 38C1 , Figure 38C2 , Figure 38D1 , Figure 38D2 , Figure 38E1 as well as Figure 38E2 These are TEM-EDX surface analysis images of the positive electrode active material of Example 2;

[0086] Figure 39A , Figure 39B1 , Figure 39B2 , Figure 39C1 , Figure 39C2 , Figure 39D1 , Figure 39D2 , Figure 39E1 as well as Figure 39E2 These are TEM-EDX surface analysis images of a comparative example from Example 2;

[0087] Figure 40A , Figure 40B1 , Figure 40B2 , Figure 40C1 , Figure 40C2, Figure 40D1 , Figure 40D2 , Figure 40E1 as well as Figure 40E2 These are TEM-EDX surface analysis images of the positive electrode active material of Example 2;

[0088] Figure 41A and Figure 41B This is a graph showing the EDX point analysis results of Example 2;

[0089] Figure 42A and Figure 42B This is a graph showing the EDX point analysis results of Example 2;

[0090] Figure 43 This is a graph showing the charge / discharge rate characteristics of the secondary battery in Example 2;

[0091] Figure 44 This is a graph showing the temperature characteristics of the secondary battery in Example 2;

[0092] Figure 45 This is a graph showing the cycle characteristics of the secondary battery of Example 2;

[0093] Figure 46A and Figure 46B This is a graph showing the XPS analysis results of the positive electrode active material of Example 3;

[0094] Figure 47A and Figure 47B This is a graph showing the cycle characteristics of a secondary battery containing the positive electrode active material of Example 3;

[0095] Figure 48 This is a graph showing the cycle characteristics of a secondary battery containing the positive electrode active material of Example 3;

[0096] Figure 49 This is a graph showing the cycle characteristics of a secondary battery containing the positive electrode active material of Example 3;

[0097] Figures 50A to 50C This is a graph showing the charge-discharge characteristics of a secondary battery containing the positive electrode active material of Example 3;

[0098] Figures 51A to 51C This is an SEM image of the positive electrode active material of Example 4;

[0099] Figure 52A-1 , Figure 52A-2 , Figure 52B-1 , Figure 52B-2 , Figure 52C-1 as well as Figure 52C-2 Here is a SEM-EDX image of the positive electrode active material of Example 4;

[0100] Figure 53This is the process flow diagram for Example 5;

[0101] Figure 54 This is a diagram illustrating the spray drying equipment of Example 5;

[0102] Figure 55 This is a TEM image illustrating one embodiment of the present invention, as shown in Example 5;

[0103] Figure 56 This is a SEM image illustrating one embodiment of the present invention, as shown in Example 5;

[0104] Figure 57 These are SEM images illustrating a comparative example of Example 5;

[0105] Figure 58A and Figure 58B This is a cross-sectional view of the active material layer containing graphene compound as a conductive additive in Example 5. Detailed Implementation

[0106] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following description, and those skilled in the art will readily understand that its methods and details can be varied in various forms. Furthermore, the present invention should not be construed as being limited solely to the contents described in the following embodiments.

[0107] Note that in the accompanying drawings described in this specification, the size or thickness of various components such as the positive electrode, negative electrode, active material layer, separator, and outer packaging may sometimes be exaggerated for clarity. Therefore, the size of each component is not limited to its individual dimensions, nor is it limited to the relative sizes between the components.

[0108] Note that in the structure of the present invention described in this specification and other documents, the same symbol is used to denote the same part or part with the same function in different figures, and repeated descriptions are omitted. In addition, sometimes the same shaded line is used to denote parts with the same function, without special additional reference numerals.

[0109] In this specification, Miller indices are used to represent crystal planes and orientations. When using Miller indices, a superscript is placed before the numbers in crystallography. However, in this specification, due to the notation limitations in the patent application, a negative sign (-) is sometimes placed before the numbers to represent crystal planes and orientations instead of a superscript. Furthermore, "[]" indicates the individual orientation within the crystal, "<>" indicates the aggregate orientation of all equivalent crystal directions, "()" indicates the individual orientation of a crystal plane, and "{}" indicates an aggregate of planes with equivalent symmetry. In the accompanying drawings, a superscript is placed before the numbers to represent the formal crystallographic representation of crystal planes and orientations. Furthermore, It is 10 -10 m.

[0110] In this specification and the like, segregation refers to the phenomenon in which a certain element (e.g., B) is not uniformly distributed in a solid containing multiple elements (e.g., A, B, C).

[0111] In this specification, the layered rock-salt type crystal structure of composite oxides containing lithium and transition metals refers to a crystal structure with a rock-salt type ionic arrangement of alternating cations and anions, and a two-dimensional plane formed by the regular arrangement of transition metals and lithium, thus allowing lithium to diffuse in two dimensions. Furthermore, it may also include defects such as vacancies of cations or anions. Strictly speaking, the layered rock-salt type crystal structure is sometimes a lattice deformation structure of rock-salt type crystals.

[0112] In this specification and other materials, a rock-salt type crystal structure refers to a structure in which cations and anions are arranged alternately. Furthermore, it may also include vacancies of cations or anions.

[0113] Layered rock salt crystals and rock salt crystals contain anions that form a cubic closest-packed structure (face-centered cubic lattice structure). When layered rock salt crystals and rock salt crystals come into contact, there are crystal faces with consistent orientation of the cubic closest-packed structure formed by anions. The space group of layered rock salt crystals is R-3m, which is different from the space group Fm-3m of general rock salt crystals and the space group Fd-3m of rock salt crystals with the simplest symmetry. Therefore, the Miller indices of the crystal faces satisfying the above conditions are different between layered rock salt crystals and rock salt crystals. In this specification, sometimes the consistent orientation of the cubic closest-packed structure formed by anions in layered rock salt crystals and rock salt crystals refers to a substantially consistent crystal orientation.

[0114] The consistency of crystal orientation between two regions can be determined based on transmission electron microscopy (TEM) images, scanning transmission electron microscopy (STEM) images, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, and annular bright-field scanning transmission electron microscopy (ABF-STEM) images. Additionally, X-ray diffraction, electron diffraction, and neutron diffraction can be used as diagnostic criteria. In TEM images, the arrangement of cations and anions is observed as repetition of bright and dark lines. When the orientations of layered rock salt crystals and the cubic close-packed structures within rock salt crystals are consistent, the angle formed by the repetition of bright and dark lines in the layered rock salt crystals and rock salt crystals is observed to be less than 5 degrees, more preferably less than 2.5 degrees. Note that sometimes light elements such as oxygen and fluorine cannot be clearly observed in TEM images; in such cases, the consistency of orientation can be determined based on the arrangement of metallic elements.

[0115] In this specification, the state in which the structure of a two-dimensional interface is similar is called "epitaxy". Furthermore, crystal growth with a similar structure of a two-dimensional interface is called "epitaxy growth". Additionally, the state having three-dimensional structural similarity or the same crystallographic orientation is called "topological derivation". Therefore, in the case of topological derivation, when observing a portion of the cross-section, the crystallographic orientations of the two regions (e.g., the base region and the region formed by growth) are substantially consistent.

[0116] (Implementation Method 1)

[0117] [Structure of the positive electrode active material]

[0118] First, refer to Figures 1A to 1C This describes a positive electrode active material 100 according to one embodiment of the present invention. The positive electrode active material 100 refers to a material containing a transition metal capable of electrochemically inserting and deintercalating lithium ions. For example... Figure 1A As shown, the positive electrode active material 100 includes a first region 101 inside and a second region 102 and a third region 103 on its surface.

[0119] like Figure 1B As shown, the second region 102 does not necessarily need to cover the entire first region 101. Similarly, the third region 103 does not necessarily need to cover the entire second region 102. The third region 103 can exist in contact with the first region 101.

[0120] The thickness of the second region 102 and the third region 103 can also vary depending on their location.

[0121] Furthermore, the third region 103 can exist within the positive electrode active material 100. For example, if the first region 101 is polycrystalline, the third region 103 can exist near the grain boundaries. Additionally, the third region 103 can also exist in or near portions of the positive electrode active material 100 with crystal defects, cracks, or similar features. Figure 1B In the diagram, a portion of a grain boundary is represented by a dashed line. In this specification, crystal defects refer to defects that can be observed in TEM images, such as structures or voids where other elements have entered the crystal. Furthermore, cracks refer to... Figure 1C Cracks or damage formed in particles, as shown in crack section 106.

[0122] Similarly, such as Figure 1BAs shown, the second region 102 can exist inside the positive electrode active material 100. For example, if the first region 101 is polycrystalline, the second region 102 can also exist near the grain boundary. Furthermore, the second region 102 can also exist in or near portions of the positive electrode active material 100 with crystal defects, cracks, or elsewhere. Additionally, the third region 103 located inside the positive electrode active material 100 overlaps with the second region 102.

[0123] <Region 1, 101>

[0124] The first region 101 comprises a composite oxide of lithium and a first transition metal. In other words, the first region 101 comprises lithium, the first transition metal, and oxygen.

[0125] The composite oxide of lithium and the first transition metal preferably has a layered rock salt-type crystal structure.

[0126] As the first transition metal, cobalt can be used alone, or cobalt and manganese can be used, or cobalt, manganese and nickel can be used.

[0127] That is to say, the first region may include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which manganese replaces part of the cobalt, nickel-manganese-cobalt oxide, etc. In addition to transition metals, the first region 101 may also include metals other than transition metals such as aluminum.

[0128] The first region 101 serves as a region that is particularly conducive to the charge-discharge reaction in the positive electrode active material 100. In order to increase the capacity of the secondary battery containing the positive electrode active material 100, the volume of the first region 101 is preferably larger than that of the second and third regions.

[0129] Materials with a layered rock-salt-type crystal structure have characteristics such as high discharge energy or low electrical resistance due to the two-dimensional diffusion of lithium, so this structure is preferred as the first region 101. In addition, when the first region 101 has a layered rock-salt-type crystal structure, unexpectedly, segregation of main group elements such as magnesium, which will be described later, tends to occur.

[0130] The first region 101 can be either single-crystal or polycrystalline. For example, the first region 101 can be polycrystalline with an average grain size of 280 nm or more and 630 nm or less. When the first region 101 is polycrystalline, grain boundaries can sometimes be observed using TEM or similar methods. Furthermore, the average grain size can be calculated from the half-width at half-maximum (HWHM) of the XRD.

[0131] Because polycrystalline materials have a distinct crystal structure, they ensure a sufficient two-dimensional diffusion path for lithium ions. Furthermore, polycrystalline materials are easier to produce than monocrystalline materials, making polycrystalline materials the preferred choice for the first region 101.

[0132] Furthermore, the first region 101 as a whole does not necessarily need to have a layered rock salt type crystal structure. For example, a portion of the first region 101 may be amorphous or have other crystal structures.

[0133] <Second Region 102>

[0134] The second region 102 contains an oxide of the second transition metal. That is, the second region 102 contains the second transition metal and oxygen.

[0135] As the second transition metal, a non-uniform metal is preferred. That is, the second region 102 preferably contains a non-uniform compound. For example, at least one of titanium, vanadium, manganese, iron, chromium, niobium, cobalt, zinc, zirconium, nickel, etc., can be used as the second transition metal. Note that the second transition metal is preferably an element different from the first transition metal.

[0136] In this specification, etc., non-uniform metals refer to metals capable of having multiple atomic valences. Furthermore, non-uniform compounds refer to compounds of metals and other elements capable of having multiple atomic valences.

[0137] Furthermore, the second region 102 preferably has a rock salt-type crystal structure.

[0138] The second region 102 serves as a buffer region connecting the first region 101 and the third region 103, described later. In non-uniform compounds, the interatomic distance can vary depending on the valence of the metal contained in the non-uniform compound. Furthermore, in non-uniform compounds, cation or anion vacancies and dislocations (so-called Magneille phases) often form. Thus, the second region 102, acting as a buffer region, can absorb the skew that occurs between the first region 101 and the third region 103.

[0139] In addition to containing the second transition metal and oxygen, the second region 102 may also contain lithium. For example, it may also contain lithium titanate, lithium manganese oxide, etc. Furthermore, the second region 102 may also contain the main group elements contained in the third region 103, which will be described later. The second region 102 is preferably used as a buffer region and contains elements such as lithium contained in the first region 101 and the third region 103.

[0140] In other words, the second region 102 may contain lithium titanate, titanium oxide, vanadium oxide, manganese oxide, iron oxide, copper oxide, chromium oxide, niobium oxide, cobalt oxide, zinc oxide, etc.

[0141] Furthermore, the second region 102 may contain a first transition metal. For example, a second transition metal may be present in a portion of the first transition metal position of the composite oxide containing the first transition metal.

[0142] For example, when the second transition metal is titanium, titanium can exist in the second region 102 as titanium oxide (TiO2) or lithium titanate (LiTiO2). Alternatively, in the second region 102, titanium can replace part of the first transition metal position of the composite oxide containing lithium and the first transition metal.

[0143] Furthermore, the second region 102 may also contain fluorine.

[0144] The crystal structure of the second region 102 is preferably the same as that of the third region 103, which will be described later. In this case, the crystal orientations of the second region 102 and the third region 103 are likely to be consistent.

[0145] The second region 102 preferably has a rock salt crystal structure, but the second region 102 as a whole does not necessarily need to have a rock salt crystal structure. For example, the second region 102 may also have other crystal structures such as spinel crystal structure, olivine crystal structure, corundum crystal structure, rutile crystal structure, etc.

[0146] Furthermore, as long as the structure of six oxygen atoms adjacent to cations is maintained, the crystal structure can be skewed. Additionally, cation vacancies can exist in a portion of the second region 102.

[0147] In addition, a portion of the second region 102 can also be amorphous.

[0148] When the second region 102 is too thin, its function as a buffer region is reduced; however, when the second region 102 is too thick, it may lead to a reduction in capacity. Therefore, the second region 102 is preferably located at a position of 20 nm from the surface of the positive electrode active material 100, and more preferably at a position of 10 nm (in the depth direction). The second transition metal may have a concentration gradient.

[0149] <Region 3, 103>

[0150] Region 103 contains compounds of main group elements. These main group element compounds are integral ratio compounds. Preferably, the main group element compounds are those composed of electrochemically stable main group elements; for example, at least one of magnesium oxide, calcium oxide, beryllium oxide, lithium fluoride, and sodium fluoride may be used.

[0151] When the positive electrode active material 100 is used in a secondary battery, the third region 103 is in contact with the electrolyte. Therefore, as the material used for the third region 103, it is preferable to use a material that experiences minimal electrochemical changes during charge-discharge processes and is not easily degraded due to contact with the electrolyte. A compound of a main group element that is electrochemically stable and has an integral ratio is preferably used in the third region 103. The positive electrode active material 100 includes the third region 103 in its surface portion to improve the charge-discharge stability of the secondary battery. Here, high stability of the secondary battery means that the crystal structure of the composite oxide containing lithium and a first transition metal in the first region 101 is more stable. Alternatively, it means that the capacity of the secondary battery changes little even after repeated charge-discharge cycles; and that the valence changes of the metal contained in the positive electrode active material 100 are suppressed even after repeated charge-discharge cycles.

[0152] Region 103 may contain fluorine. In the case where Region 103 contains fluorine, fluorine can replace some of the anions in compounds containing main group elements.

[0153] The diffusivity of lithium can be improved by replacing some of the anions in compounds containing main group elements with fluorine. As a result, the third region 103 is less likely to hinder charging and discharging. Furthermore, the presence of fluorine on the surface of the positive electrode active material particles sometimes improves resistance to corrosion from hydrofluoric acid produced by electrolyte decomposition.

[0154] Furthermore, the third region 103 may also contain lithium, a first transition metal, and a second transition metal.

[0155] Compounds containing main group elements in the third region 103 preferably have a rock salt-type crystal structure. When the third region 103 has a rock salt-type crystal structure, the crystal orientations of the third region 103 and the second region 102 tend to be consistent. When the crystal orientations of the first region 101, the second region 102, and the third region 103 are substantially consistent, the second region 102 and the third region 103 can be used as a more stable coating layer.

[0156] However, the third region 103 as a whole does not necessarily need to have a rock salt crystal structure. For example, the third region 103 can also have other crystal structures such as spinel crystal structure, olivine crystal structure, corundum crystal structure, rutile crystal structure, etc.

[0157] Furthermore, the crystal structure can be skewed as long as the six oxygen atoms are adjacent to the cations. Additionally, cation vacancies can exist in a portion of the third region 103.

[0158] In addition, a portion of the third region 103 can also be amorphous.

[0159] When the third region 103 is too thin, its function in improving charge and discharge stability is reduced; however, when the third region 103 is too thick, it may lead to a reduction in capacity. Therefore, the thickness of the third region 103 is preferably 0.5 nm or more and 50 nm or less, more preferably 0.5 nm or more and 2 nm or less.

[0160] When the third region 103 contains fluorine, the fluorine is preferably present in a bond state other than magnesium fluoride (MgF2), lithium fluoride (LiF), and cobalt fluoride (CoF2). Specifically, when XPS analysis is performed on the vicinity of the surface of the positive electrode active material 100, the bond energy peak of fluorine is preferably located between 682 eV and 685 eV, more preferably around 684.3 eV. This bond energy is not equivalent to the bond energies of MgF2, lithium fluoride, and cobalt fluoride.

[0161] In this specification, the peak position of the bond energy of an element in XPS analysis refers to the bond energy value that yields the strongest energy spectrum within the range corresponding to the bond energy of that element.

[0162] Generally, repeated charge-discharge cycles cause the following side reactions in the positive electrode active material: dissolution of first transition metals such as manganese, cobalt, and nickel in the electrolyte; oxygen desorption; and instability of the crystal structure, leading to degradation of the positive electrode active material. However, the positive electrode active material 100 of one embodiment of the present invention includes a second region 102 serving as a buffer region and a third region 103 that is electrochemically stable. This effectively suppresses the dissolution of the first transition metal, making the crystal structure of the lithium and transition metal composite oxide contained in the first region 101 more stable. As a result, the cycle characteristics of the secondary battery containing the positive electrode active material 100 can be significantly improved. Furthermore, when at voltages above 4.3V (vs. Li / Li + The voltage, especially, 4.5V (vs. Li / Li) + When charging and discharging at high voltages (above 1000V), the structure of one embodiment of the present invention exhibits significant effects.

[0163] <Heteroepithelial growth and topological derivation>

[0164] 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. The regions formed by heteroepitaxial growth become topological derivatives whose crystal orientation is substantially consistent in three dimensions with the regions used as the substrate. Thus, the first region 101, the second region 102, and the third region 103 can all be topologically derived.

[0165] When the crystal orientations from the first region 101 to the third region 103 are substantially consistent, the second region 102 and the third region 103 serve as a coating layer having a stable bond with the first region 101. As a result, a positive electrode active material 100 containing a strong coating layer can be provided.

[0166] Because the second region 102 and the third region 103 have a stable bond with the first region 101, changes in the crystal structure of the first region 101 caused by charging and discharging can be effectively suppressed when the positive electrode active material 100 is used in a secondary battery. Even if lithium is deintercalated from the first region 101 during charging, the coating layer with a stable bond can suppress the deintercalation of cobalt and oxygen from the first region 101. Furthermore, chemically stable materials can be used in the regions in contact with the electrolyte. Thus, a secondary battery with excellent cycle characteristics can be provided.

[0167] <Mismatch between regions>

[0168] In order to achieve heteroepitaxial growth, the mismatch between the crystal in the region used as the substrate and the crystal from which the crystal is grown is important.

[0169] In this specification, the mismatch degree f is defined by the following formula 1. Let a represent the average closest distance between oxygen and cation in the crystal in the region used as the substrate, and let b represent the average closest distance between native anions and cations in the crystal from which the crystal is grown.

[0170] [Equation 1]

[0171]

[0172] To achieve heteroepitaxial growth, the mismatch f between the crystal in the substrate region and the crystal from which the crystal is grown needs to be 0.12 or less. To achieve more stable layered heteroepitaxial growth, the mismatch f is preferably 0.08 or less, and more preferably 0.04 or less.

[0173] Therefore, it is preferable to select the materials of the first region 101 and the second region 102 in such a way that the mismatch 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 0.12.

[0174] Furthermore, it is preferable to select the materials of the second region 102 and the third region 103 in such a way that the mismatch 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 0.12.

[0175] Examples of materials and crystal faces of the first region 101, the second region 102, and the third region 103 are shown below, which satisfy the condition that the mismatch 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 0.12 and the mismatch 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 0.12.

[0176] Example 1: Lithium cobalt oxide, lithium titanate, and magnesium oxide

[0177] First, refer to Figure 2A , Figure 2B as well as Figure 3 The first transition metal is cobalt, the first region 101 contains lithium cobalt oxide with a layered rock salt crystal structure, the second transition metal is titanium, the second region 102 contains lithium titanate with a rock salt crystal structure, and the compound of the main group element in the third region 103 is an example of magnesium oxide with a rock salt crystal structure.

[0178] Figure 2A Crystal structure models of lithium cobalt oxide (LiCoO2) in layered rock salt form (space group R-3mH), lithium titanate (LiTiO2) in rock salt form (space group Fd-3mZ), and magnesium oxide in rock salt form (space group Fd-3mZ) are shown. Figure 2A The model is shown when viewed from the b-axis direction.

[0179] from Figure 2A From this perspective, layered rock salt crystals and rock salt crystals cannot be said to be topologically derived. Here, from different directions (e.g., Figure 2A (The direction indicated by the arrow in the image) is used to examine layered rock salt crystals. Figure 2B This shows the model of layered rock salt crystals viewed from the <1-1-4> crystal plane and from... <100> The model is based on the crystal plane orientation when viewing rock salt-type crystals.

[0180] like Figure 2B As shown, when viewing a layered rock salt crystal from the <1-1-4> crystal plane, the atomic arrangement of the layered rock salt crystal is different from that viewed from the <1-1-4> crystal plane. <100> The atomic arrangement of rock-salt type crystals is very similar when viewed along crystal planes. Furthermore, the closest distance between the metal and oxygen atoms also takes similar values. For example, in layered rock-salt type lithium cobalt oxide, the distance between Li and O is... And the distance between Co and O is In rock-salt lithium titanate, the distance between Li and O is... And the distance between Ti and O is In rock salt-type magnesium oxide, the distance between Mg and O is...

[0181] The following is for reference Figure 3 Explain the degree of mismatch between regions when the (1-1-4) crystal plane of a layered rock salt crystal is in contact with the {100} crystal plane of a rock salt crystal.

[0182] like Figure 3 As shown, the metal-oxygen-metal distance of the (1-1-4) crystal plane 101p(1-1-4) of lithium cobalt oxide with a layered rock-salt type crystal structure in the first region 101 is... Furthermore, the metal-oxygen-metal distance of the {100} crystal plane 102p{100} of lithium titanate with a rock-salt-type crystal structure in the second region 102 is... Therefore, the mismatch f between crystal plane 101p(1-1-4) and crystal plane 102p{100} is 0.04.

[0183] Furthermore, in the third region 103, the metal-oxygen-metal distance of the {100} crystal plane 103p{100} of magnesium oxide with a rock-salt-type crystal structure is... Therefore, the mismatch f between crystal plane 102p{100} and crystal plane 103p{100} is 0.02.

[0184] In this way, the mismatch between the first region 101 and the second region 102 and the mismatch between the first region 102 and the third region 103 are very small, so the first region 101, the second region 102 and the third region 103 can be topologically derived.

[0185] Although Figure 3 Not illustrated, but the mismatch f is 0.05 when the crystal plane 101p(1-1-4) in the first region 101 contacts the crystal plane 103p{100} in the third region 103. That is, the mismatch can be reduced by means of the second region 102. Furthermore, by means of the second region 102, which is a transition metal oxide having an integrity compound, the first region 101, the second region 102, and the third region 103 can be more stably topologically derived. Thus, the second region 102 and the third region 103 can be used as a coating layer having a stable bond with the first region 101.

[0186] In this embodiment, an example is described where the (1-1-4) crystal plane of a layered rock salt crystal is in contact with the {100} crystal plane of a rock salt crystal; however, one embodiment of the present invention is not limited to this. Any topologically derived crystal planes in contact with each other are acceptable.

[0187] Example 2: Lithium cobalt oxide, manganese oxide, and calcium oxide

[0188] The first transition metal is cobalt, the first region 101 contains lithium cobalt oxide with a layered rock salt crystal structure, the second transition metal is manganese, the second region 102 contains manganese oxide with a rock salt crystal structure, and the compound of the main group element in the third region 103 is an example of calcium oxide with a rock salt crystal structure.

[0189] In this case, with Figure 2A , Figure 2B as well as Figure 3 Similarly, when viewing the layered rock salt crystal in the first region 101 from the <1-1-4> crystal plane direction, the atomic arrangement of the layered rock salt crystal is the same as that viewed from the <1-1-4> crystal plane direction. <100> The atomic arrangement of the rock salt-type crystals in the second region 102 and the third region 103 is very similar when viewed from the crystal plane.

[0190] The following describes the mismatch between regions when the (1-1-4) crystal plane of a layered rock-salt type crystal and the {100} crystal plane of a rock-salt type crystal are in contact with each other. The metal-oxygen-metal distance between the (1-1-4) crystal plane of lithium cobalt oxide with a layered rock-salt type crystal structure in the first region 101 is... Furthermore, the metal-oxygen-metal distance of the {100} crystal plane of manganese oxide with a rock-salt-type crystal structure in the second region 102 is... Therefore, the mismatch f between the (1-1-4) crystal plane in the first region 101 and the {100} crystal plane in the second region 102 is 0.11.

[0191] Furthermore, the metal-oxygen-metal distance of the {100} crystal plane of calcium oxide with a rock-salt-type crystal structure in region 103 is... Therefore, the mismatch f between the {100} crystal plane in the second region 102 and the {100} crystal plane in the third region 103 is 0.08.

[0192] In this way, the mismatch between the first region 101 and the second region 102 and the mismatch between the first region 102 and the third region 103 are very small, so the first region 101, the second region 102 and the third region 103 can be topologically derived.

[0193] If the (1-1-4) crystal plane in the first region 101 contacts the {100} crystal plane in the third region 103, the mismatch f is 0.20, making heteroepitaxial growth difficult. In other words, by means of the second region 102, the first to third regions can be heteroepitaxially grown. Therefore, the second region 102 and the third region 103 can be used as cladding layers with a stable bond to the first region 101.

[0194] Example 3: Lithium nickel-manganese-cobalt oxide, manganese oxide, and calcium oxide

[0195] The first transition metals are nickel, manganese, and cobalt, and the first region 101 contains lithium nickel-manganese-cobalt oxide (LiNi) with a layered rock-salt-type crystal structure. 0.33 Co 0.33 Mn 0.33 O2), the second transition metal is manganese, the second region 102 contains manganese oxide with a rock salt-type crystal structure, and the compound of the main group element in the third region 103 is an example of calcium oxide with a rock salt-type crystal structure.

[0196] In this case, such as Figure 2A , Figure 2B as well as Figure 3 As shown, when viewing a layered rock salt crystal from the <1-1-4> crystal plane, the atomic arrangement of the layered rock salt crystal is different from that viewed from the <1-1-4> crystal plane. <100> The atomic arrangement of rock salt crystals is very similar when viewed from the crystal plane direction. The following describes the degree of mismatch between different regions when the (1-1-4) crystal plane of a layered rock salt crystal and the {100} crystal plane of a rock salt crystal are in contact with each other.

[0197] The metal-oxygen-metal distance between the (1-1-4) crystal planes of lithium nickel-manganese-cobalt oxide with a layered rock-salt-type crystal structure in region 101 is... Furthermore, the metal-oxygen-metal distance of the {100} crystal plane of manganese oxide with a rock-salt-type crystal structure in the second region 102 is... Therefore, the mismatch f between the (1-1-4) crystal plane in the first region 101 and the {100} crystal plane in the second region 102 is 0.09.

[0198] Furthermore, the metal-oxygen-metal distance of the {100} crystal plane of calcium oxide with a rock-salt-type crystal structure in region 103 is... Therefore, the mismatch f between the {100} crystal plane in the second region 102 and the {100} crystal plane in the third region 103 is 0.08.

[0199] In this way, the mismatch between the first region 101 and the second region 102 and the mismatch between the first region 102 and the third region 103 are very small, so the first region 101, the second region 102 and the third region 103 can be topologically derived.

[0200] If the (1-1-4) crystal plane in the first region 101 contacts the {100} crystal plane in the third region 103, the mismatch degree f is 0.18, making heteroepitaxial growth difficult. In other words, by means of the second region 102, the first to third regions can be heteroepitaxially grown. Therefore, the second region 102 and the third region 103 can be used as cladding layers with a stable bond to the first region 101.

[0201] <Boundaries between regions>

[0202] As described above, the compositions of the first region 101, the second region 102, and the third region 103 are different. The elements contained in each region sometimes exhibit a concentration gradient. For example, the second transition metal contained in the second region 102 sometimes exhibits a concentration gradient. Furthermore, since the third region 103 is preferably a region where the segregation of main group elements (described later) occurs, it sometimes exhibits a concentration gradient of main group elements. Therefore, the boundaries between the regions are sometimes indistinct.

[0203] Based on TEM images, STEM images, Fast Fourier Transform (FFT) analysis, Energy Dispersive X-ray Analysis (EDX), Depth Direction Analysis using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy, and Thermal Desorption Spectroscopy (TDS), the compositional differences between the first region 101, the second region 102, and the third region 103 can be confirmed.

[0204] For example, in TEM and STEM images, differences in constituent elements are observed as differences in brightness; therefore, it can be observed that the constituent elements of the first region 101, the second region 102, and the third region 103 are different from each other. Furthermore, in EDX surface analysis (e.g., element mapping), it can also be observed that the first region 101, the second region 102, and the third region 103 contain different elements.

[0205] Furthermore, in line analysis using EDX and depth-direction analysis using ToF-SIMS, the concentration peaks of each element contained in the first region 101, the second region 102, and the third region 103 can be detected.

[0206] However, it is not always possible to observe a clear boundary between the first region 101, the second region 102, and the third region 103 in various analyses.

[0207] In this specification, it is assumed that the third region 103 existing in the surface portion of the positive electrode active material 100 extends from the surface of the positive electrode active material 100 to a region where the concentration of main group elements such as magnesium, detected by depth direction analysis, reaches one-fifth of the peak value. As a depth direction analysis method, line analysis using EDX and depth direction analysis using ToF-SIMS, etc., can be used.

[0208] Furthermore, the concentration peak of the main group element preferably appears in a region with a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably in a region with a depth of 1 nm, and even more preferably in a region with a depth of 0.5 nm.

[0209] Although the depth at which the concentration of main group elements reaches 1 / 5 of the peak varies depending on the manufacturing method, in the case of the manufacturing method described later, this depth is approximately 2 nm to 5 nm away from the surface of the positive electrode active material.

[0210] The third region 103, which exists within the first region 101 near grain boundaries or crystal defects, refers to the region where the concentration of main group elements detected by depth direction analysis is more than 1 / 5 of the peak value.

[0211] The fluorine distribution of the positive electrode active material 100 preferably overlaps with the distribution of the main group elements mentioned above. Therefore, it is preferable that fluorine also has a concentration gradient, with the concentration peak of fluorine appearing in a region at a depth of 3 nm from the surface of the positive electrode active material 100 towards the center, more preferably in a region at a depth of 1 nm, and even more preferably in a region at a depth of 0.5 nm.

[0212] In this specification, the second region 102 present in the surface layer of the positive electrode active material 100 refers to a region where the concentration of the second transition metal detected by depth direction analysis is more than half of the peak value. The second region 102 present within the first region 101 near grain boundaries or crystal defects refers to a region where the concentration of the second transition metal detected by depth direction analysis is more than half of the peak value. As analytical methods, line analysis using EDX and depth direction analysis using ToF-SIMS, etc., can be used.

[0213] Therefore, the third region 103 sometimes overlaps with the second region 102. Preferably, the third region 103 exists in a region closer to the surface of the positive electrode active material particle than the second region 102. Furthermore, the concentration peak of the main group element preferably appears in a region closer to the surface of the positive electrode active material particle than the concentration peak of the second transition metal.

[0214] The peak of the second transition metal preferably appears in a region with a depth of 0.2 nm or more and 10 nm or less from the surface of the positive electrode active material 100 toward the center, and more preferably in a region with a depth of 0.5 nm or more and 3 nm or less.

[0215] XPS measures a region from the surface of the particles of the positive electrode active material 100 to a depth of approximately 5 nm. Therefore, the elemental concentrations at a position approximately 5 nm from the surface can be quantitatively analyzed. Consequently, the elemental concentrations in the third region 103 and the second region 102, which exist at a distance of approximately 5 nm from the surface, can be quantitatively analyzed.

[0216] When XPS analysis is performed on the surface of the positive electrode active material 100, the relative value of the concentration of the second transition metal when the concentration of the first transition metal is 1 is preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.3 or less. Furthermore, the relative value of the concentration of the main group elements is preferably 0.4 or more and 1.5 or less, more preferably 0.45 or more and 1.00 or less. Furthermore, the relative value of the concentration of fluorine is preferably 0.05 or more and 1.5 or less, more preferably 0.3 or more and 1.00 or less.

[0217] As described above, since each of the elements contained in the first region 101, the second region 102, and the third region 103 sometimes has a concentration gradient, the first region 101 may also contain elements such as fluorine contained in the second region 102 or the third region 103. Similarly, the third region 103 may also contain elements contained in the first region 101 or the second region 102. The first region 101, the second region 102, and the third region 103 may also contain other elements such as carbon, sulfur, silicon, sodium, calcium, chlorine, and zirconium.

[0218] [Particle size]

[0219] When the particle size of the positive electrode active material 100 is too large, lithium diffusion becomes difficult. On the other hand, when the particle size of the positive electrode active material 100 is too small, maintaining the crystal structure described below becomes difficult. Therefore, D50 (also known as median particle size) is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 70 μm or less. When a 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 is preferably substantially equal to the maximum particle size of the positive electrode active material 100. When the particle size is less than 5 μm and a spray drying device with a nozzle diameter of 20 μm is used, secondary particles are accumulated and covered, which leads to a decrease in coverage.

[0220] Furthermore, to achieve a high density of the positive electrode active material layer, mixing large particles (with the longest portion being approximately 20 μm or more and less than 40 μm) and small particles (with the longest portion being approximately 1 μm) and using the small particles to fill the gaps between the large particles is also effective. Therefore, the particle size distribution can have more than two peaks.

[0221] The particle size of the positive electrode active material is affected not only by the particle size of the starting material, but also by the ratio of lithium to the first transition metal contained in the starting material (hereinafter referred to as the ratio of Li to the first transition metal).

[0222] When the particle size of the starting material is small, it is necessary to grow the particles during calcination in order to set the particle size of the positive electrode active material to the above-mentioned preferred range.

[0223] To promote particle growth during calcination, the ratio of Li to the first transition metal in the starting material is set to be greater than 1, meaning that the amount of lithium is increased. For example, when the ratio of Li to the first transition metal is around 1.06, it is easy to obtain a positive electrode active material with a D50 of 15 μm or more. Note that, as described below, during the formation step of the positive electrode active material, lithium sometimes detaches from the system, and therefore the ratio of lithium to the first transition metal in the obtained positive electrode active material is sometimes not equal to the ratio of lithium to the first transition metal in the starting material.

[0224] However, when excessive lithium is used to set the particle size within the preferred range described above, the capacity retention of the secondary battery containing the positive electrode active material may decrease.

[0225] The inventors have discovered that by using the second region 102 containing the second transition metal in the surface layer, the ratio of Li to the first transition metal can be controlled to set an optimal particle size range, and a positive electrode active material with high capacity retention can be formed.

[0226] In the positive electrode active material of one embodiment of the present invention, including the region containing the second transition metal located in the surface layer, the ratio of Li to the first transition metal in the starting material is preferably 1.00 or more and 1.07 or less, more preferably 1.03 or more and 1.06 or less.

[0227] [The formation of the second region]

[0228] The second region 102 can be formed by covering lithium and first transition metal composite oxide particles with a material containing the second transition metal.

[0229] As a method for covering with a material containing a second transition metal, liquid phase methods such as sol-gel methods, solid phase methods, sputtering methods, vapor deposition methods, CVD (chemical vapor deposition) methods, and PLD (pulsed laser deposition) methods can be used. In this embodiment, the case of using the sol-gel method, which can achieve uniform coverage at atmospheric pressure, will be described.

[0230] Sol-gel method

[0231] Reference Figure 4A-1 , Figure 4A-2 , Figure 4A-3 , Figure 4B , Figure 4C , Figure 4D-1 as well as Figure 4D-2 This describes the use of the sol-gel method to form materials containing a second transition metal.

[0232] First, the alkoxide of the second transition metal is dissolved in alcohol.

[0233] Figure 4A-1The general formula for alkoxides of second transition metals is shown. In Figure 4A-1 In the general formula, M2 represents an alkoxide of a second transition metal. R represents an alkyl group with 1 to 18 carbon atoms, or an aryl group with 6 to 13 carbon atoms, whether substituted or unsubstituted. Although in Figure 4A-1 The diagram shows a general formula for a second transition metal having a tetravalent oxidation state, but one embodiment of the invention is not limited thereto. The second transition metal may also have a divalent, trivalent, pentavalent, hexavalent, or heptavalent oxidation state. In this case, the alkoxide of the second transition metal comprises an alkoxy group corresponding to the valence of the second transition metal.

[0234] Figure 4A-2 The general formula for titanium alkoxides is shown when titanium is used as the second transition metal. Figure 4A-2 In this context, R represents an alkyl group having 1 to 18 carbon atoms, or an aryl group having 6 to 13 carbon atoms, whether substituted or unsubstituted.

[0235] As titanium alkoxides, tetramethoxy titanium, tetraethoxy titanium, tetran-n-propoxy titanium, tetraisopropoxy titanium (also known as tetraisopropyl titanate, tetraisopropoxide titanium (IV), tetraisopropyl titanate, TTIP, etc.), tetran-n-butoxy titanium, tetraisobutoxy titanium, tetrasec-butoxy titanium, tetratert-butoxy titanium, etc. can be used.

[0236] Figure 4A-3 The chemical formula of tetraisopropanetitanium (IV) (TTIP), one of the titanium alkoxides described in the formation method described below, is shown.

[0237] Alcohols such as methanol, ethanol, propanol, 2-propanol, butanol, and 2-butanol are used as solvents for dissolving alkoxides of second transition metals.

[0238] Next, particles of a composite oxide of lithium, transition metal, magnesium, and fluorine are mixed in an alcoholic solution of a second transition metal alkoxide and stirred in an atmosphere containing water vapor.

[0239] By placing the solution in an atmosphere containing H2O, such as Figure 4B As shown, this causes the hydrolysis of water and the alkoxides of the second transition metals. Then, as... Figure 4C As shown, causing Figure 4B The products undergo dehydration and thickening. This is achieved through repeated induction... Figure 4B The hydrolysis shown Figure 4C The fusion reaction shown produces a sol of oxides of the second transition metal. For example... Figure 4D-1 and Figure 4D-2 As shown, the above-mentioned reaction is also induced on the composite oxide particles 110, thereby forming a layer containing a second transition metal on the surface of the particles 110.

[0240] Then, particles 110 are collected, and the alcohol is vaporized. The details of the formation method are described later.

[0241] Note that in this embodiment, an example is described where the composite oxide particles of lithium, a first transition metal, a main group element, and fluorine are covered with a material containing a second transition metal before being coated onto the positive electrode current collector. However, the present invention is not limited to this. After forming a positive electrode active material layer comprising composite oxide particles of lithium, a first transition metal, a main group element, and fluorine on the positive electrode current collector, the positive electrode current collector and the positive electrode active material layer can be immersed in an alkoxide solution of a second transition metal to cover the particles with a material containing the second transition metal.

[0242] [Speciation in the third region]

[0243] The third region 103 can also be formed by liquid-phase methods such as sputtering, solid-phase methods, and sol-gel methods. However, the inventors have discovered that when the material of the first region 101 is heated after mixing a main group element source such as magnesium and a fluorine source, the main group element segregates to the surface of the positive electrode active material particles, thereby forming the third region 103. Furthermore, the inventors have also discovered that the positive electrode active material 100 exhibits good cycle characteristics when the third region 103 is formed in this way.

[0244] In the case where the third region 103 is formed by heating as described above, the heating is preferably performed after the composite oxide particles are covered with a material containing a second transition metal element. This is because, unexpectedly, even after covering with a material containing a second transition metal element, main group elements such as magnesium segregate onto the particle surface due to heating.

[0245] Reference Figures 5A to 5C and Figures 6A to 6D The segregation models for the main group elements described above are explained. For example, the segregation models for main group elements such as magnesium can be considered to differ slightly depending on the ratio of Li to the first transition metal contained in the starting material. Therefore, referring to... Figures 5A to 5C This indicates a segregation model where the ratio of Li to the first transition metal in the starting material is less than 1.03, i.e., when the lithium content is low. (Refer to...) Figures 6A to 6D This indicates a segregation model where the ratio of Li to the first transition metal in the starting material is greater than 1.03, i.e., when the lithium content is high. Figures 5A to 5C and Figures 6A to 6D In the segregation model, the first transition metal is cobalt, the second transition metal is titanium, and the main group element is magnesium.

[0246] Figure 5AA model diagram showing the vicinity of the surface of a composite oxide particle 110 containing lithium, cobalt, magnesium, and fluorine, formed under conditions where the Li to Co ratio in the starting material is less than 1.03. Region 111 in the diagram contains lithium, cobalt, magnesium, and fluorine, with lithium cobalt oxide (LiCoO2) as the main component. Lithium cobalt oxide has a layered rock-salt type crystal structure.

[0247] It is generally believed that when synthesizing particles containing composite oxides of lithium, cobalt, magnesium, and fluorine, some lithium is detached from the system (the formed particles). This is because lithium volatilizes during calcination or dissolves in the solvent when mixing the starting materials. As a result, the ratio of Li to Co in the particles 110 containing composite oxides of lithium, cobalt, magnesium, and fluorine is sometimes smaller than the ratio of Li to Co in the starting materials.

[0248] When the Li to Co ratio in the starting material is less than 1.03, lithium readily deintercalates from lithium cobalt oxide and forms cobalt oxide on the surface of particle 110. Therefore, as... Figure 5A As shown, the surface of the composite oxide particles 110 is sometimes covered by a cobalt oxide (CoO) layer 114.

[0249] Cobalt oxide has a rock-salt type crystal structure. Therefore, in... Figure 5A In particles 110, a cobalt oxide layer 114 with a rock salt-type crystal structure is sometimes formed on and in contact with a region 111 containing lithium cobalt oxide with a layered rock salt-type crystal structure.

[0250] Particles 110 were covered with a titanium-containing material by using a sol-gel method or similar method. Figure 5B This illustrates the state of particles 110 covered with a titanium-containing layer 112 using a sol-gel method or similar technique. Figure 5B In this stage, the titanium-containing layer 112 is a gel of titanium oxide, which has low crystallinity.

[0251] Next, the particles 110 covered by the titanium-containing layer 112 are heated. Details of the heating conditions are as follows, for example, Figure 5C The diagram shows the state of a positive electrode active material 100 formed by heating particles 110 at 800°C for two hours in an oxygen atmosphere, as an embodiment of the present invention. Upon heating, titanium in the titanium-containing layer 112 diffuses into the interior of the particles 110. Simultaneously, magnesium and fluorine contained in region 111 segregate on the surface of the particles 110.

[0252] As described above, cobalt oxide with a rock-salt-type crystal structure exists on the surface of particle 110. Furthermore, magnesium oxide also has a rock-salt-type crystal structure. Therefore, it can be considered that magnesium existing on the surface of particle 110 as magnesium oxide is more stable than magnesium existing inside particle 110. This explains why magnesium segregates on the surface of particle 110 upon heating.

[0253] Furthermore, it can be argued that fluorine contained in the starting material promotes the segregation of magnesium.

[0254] Fluorine is more electronegative than oxygen. Therefore, it can be assumed that even in stable compounds such as magnesium silicate, the addition of fluorine results in an uneven charge distribution, weakening the bond between magnesium and oxygen. Furthermore, it can be argued that the replacement of oxygen in magnesium oxide with fluorine facilitates the migration of magnesium around the replaced fluorine.

[0255] Furthermore, this can also be explained by the decrease in the melting point of the mixture. When magnesium oxide (melting point 2852℃) and lithium fluoride (melting point 848℃) are added simultaneously, the melting point of magnesium oxide decreases. It can be assumed that the decrease in melting point makes magnesium more prone to migration and segregation upon heating.

[0256] Ultimately, region 103 becomes a solid solution of cobalt oxide and magnesium oxide with a rock salt-type crystal structure. Furthermore, it can be assumed that some of the oxygen contained in the cobalt oxide and magnesium oxide is replaced by fluorine.

[0257] The cobalt sites in lithium cobalt oxide are partially replaced by diffused titanium, and the lithium titanate is partially replaced by diffused titanium. The second region 102, after heating, contains lithium titanate with a rock-salt-type crystal structure.

[0258] The first region 101, after being heated, contains lithium cobalt oxide with a layered rock salt-type crystal structure.

[0259] The following is for reference Figures 6A to 6D This explains the case where the ratio of Li to Co in the starting material is 1.03 or higher. Figure 6A A model diagram showing the vicinity of the surface of a composite oxide particle 120 containing lithium, cobalt, magnesium, and fluorine, formed under conditions where the ratio of Li to Co in the starting material is 1.03 or higher. Region 121 in the figure contains lithium, cobalt, magnesium, and fluorine.

[0260] because Figure 6A The lithium content of particles 120 is sufficient, so even when lithium is extracted from particles 120 during the calcination of a composite oxide containing lithium, cobalt, magnesium and fluorine, it is replenished by lithium that diffuses from the interior of particles 120 to the surface. As a result, a cobalt oxide layer is not easily formed on the surface.

[0261] Figure 6B This illustrates the use of a titanium-containing layer 122 for covering by means of a sol-gel method or similar technique. Figure 6A The state of particle 120. In Figure 6B In this stage, the titanium-containing layer 122 is a gel of titanium oxide, which has low crystallinity.

[0262] Figure 6CShowing the to be Figure 6B The particles 120 are covered by a titanium-containing layer 122 at the beginning of heating. Upon heating, the titanium in the titanium-containing layer 122 diffuses into the interior of the particles 110. The diffused titanium combines with lithium contained in region 121 to form lithium titanate, thereby forming a lithium titanate-containing layer 125.

[0263] Because lithium combines with titanium to form lithium titanate, the amount of lithium on the surface of particle 120 is relatively insufficient. Therefore, it can be considered that: Figure 6C As shown, a cobalt oxide layer 124 is temporarily formed on the surface of particle 120.

[0264] Figure 6D Show Figure 6C The state is formed by sufficient heating to become the positive electrode active material 100 as an embodiment of the present invention. It can be considered that because a cobalt oxide layer 124 with a rock salt-type crystal structure exists on the surface, the state of magnesium as magnesium oxide present on the surface of the particle 120 is more stable than the state of magnesium present inside the particle 120. Figures 5A to 5C Similarly, fluorine promotes the segregation of magnesium.

[0265] Therefore, as Figure 6D As shown, magnesium and fluorine contained in region 121 segregate on the surface and together with cobalt oxide form the third region 103.

[0266] In this way, a positive electrode active material 100 is manufactured, comprising a third region 103 containing magnesium oxide and cobalt oxide, a second region 102 containing lithium titanate, and a first region 101 containing lithium cobalt oxide.

[0267] When main group elements segregate due to heating, if the composite oxide containing lithium and the first transition metal included in the first region 101 is polycrystalline or has crystal defects, the main group elements may segregate not only in the surface layer but also near the grain boundaries or crystal defects of the composite oxide containing lithium and the first transition metal. The segregation of main group elements near grain boundaries or crystal defects contributes to the stabilization of the crystal structure of the composite oxide containing lithium and the first transition metal included in the first region 101.

[0268] When the composite oxide comprising lithium and a first transition metal included in the first region 101 has a cracked portion, the main group element segregates into the cracked portion upon heating. In addition to the main group element, a second transition metal can also segregate. Similar to the particle surface, the cracked portion comes into contact with the electrolyte. Thus, the main group element and the second transition metal segregate into the cracked portion, generating a third region 103 and a second region 102, thereby allowing chemically stable materials to be used in the regions in contact with the electrolyte. As a result, a secondary battery with excellent cycle characteristics can be provided.

[0269] The ratio of main group element (T) to fluorine (F) in the starting material is preferably in the range of T:F = 1:x (1.5 ≤ x ≤ 4) (atomic ratio), because this facilitates efficient segregation of main group elements. Furthermore, a ratio of T:F = approximately 1:2 (atomic ratio) is more preferred.

[0270] The third region 103, formed due to segregation, is formed by epitaxial growth, so the crystal orientations of the second region 102 and the third region 103 are sometimes substantially consistent. That is, the second region 102 and the third region 103 are sometimes topologically derived. When the crystal orientations of the second region 102 and the third region 103 are substantially consistent, they are used as a better cladding layer.

[0271] However, main group elements such as magnesium added as starting materials do not necessarily need to be entirely segregated in the third region 103. For example, the first region 101 may contain small amounts of main group elements such as magnesium.

[0272] <Region 4, 104>

[0273] In addition, such as Figure 1C As shown, the positive electrode active material 100 may also include a fourth region 104 on the third region 103. Furthermore, when the positive electrode active material 100 includes defects such as cracks 106, the fourth region 104 may also exist in a manner that embeds defects such as cracks 106.

[0274] Region 104 contains a subset of the elements contained in Regions 102 and 103. For example, Region 104 contains second transition metals and main group elements.

[0275] The fourth region 104 can have protrusions, be strip-shaped, or be layered. The fourth region 104 is formed from second transition metals and main group elements contained in the starting material, etc., that are not present in the second region 102 and the third region 103. That is, by means of the fourth region 104, the content of the second transition metals and main group elements in the second region 102 and the third region 103 can sometimes be maintained within an appropriate range, thereby stabilizing the crystal structure of the second region 102 and the third region 103. Furthermore, by means of the fourth region 104, defects such as cracks 106 contained in the positive electrode active material 100 can be repaired.

[0276] The presence and shape of the fourth region 104 can be observed using scanning electron microscopy (SEM). Elements contained in the fourth region 104 can be analyzed using SEM-EDX.

[0277] [Methods for forming positive electrode active materials]

[0278] The following describes an example of a method for forming the positive electrode active material 100 according to one embodiment of the present invention.

[0279] <Step 11: Preparation of Starting Materials>

[0280] First, prepare the starting materials. From the starting materials prepared in this step, the first region 101 and the third region 103 will eventually be formed.

[0281] A lithium source and a first transition metal source are prepared as raw materials for lithium and a first transition metal contained in the first region 101. Furthermore, a main group element source is prepared as a raw material for a compound of a main group element contained in the third region 103.

[0282] In addition to the sources mentioned above, a fluorine source is preferably prepared. The fluorine used as a raw material has the effect of causing the main group elements contained in the third region 103 to segregate on the surface of the positive electrode active material 100 in subsequent steps.

[0283] For example, lithium carbonate or lithium fluoride can be used as a lithium source. For example, oxides of first transition metals can be used as a first transition metal source. For example, oxides of main group elements contained in the third region or fluorides of main group elements contained in the third region can be used as a main group element source.

[0284] As a fluorine source, lithium fluoride, fluorides of main group elements contained in the third region, etc., can be used, for example. That is to say, lithium fluoride can be used as both a lithium source and a fluorine source.

[0285] The fluorine content of the fluorine source is preferably more than 1.0 times and less than 4 times (atomic ratio) of the main group element content of the main group element source, and more preferably more than 1.5 times and less than 3 times (atomic ratio).

[0286] <Step 12: Mixing of starting materials>

[0287] Next, a lithium source, a first transition metal source, and a main group element source are mixed. Furthermore, a fluorine source is preferably added. Mixing can be performed, for example, using a ball mill or a sand mill.

[0288] <Step 13: First Heating>

[0289] Next, the material mixed in step 12 is heated. In this step, this heating is sometimes referred to as calcination or first heating. Heating is preferably performed at 800°C or higher and 1100°C or lower, more preferably at 900°C or higher and 1000°C or lower. The heating time is preferably 2 hours or higher and 20 hours or lower. Heating is preferably performed in a dry atmosphere, such as dry air. As a dry atmosphere, for example, an atmosphere with a dew point below -50°C is preferred, more preferably an atmosphere with a dew point below -100°C. In this embodiment, heating is performed under the following conditions: 1000°C; 10 hours; a heating rate of 200°C / h; and dry air with a dew point of -109°C flowing through at a rate of 10 L / min. Then, the heated material is cooled to room temperature.

[0290] By heating in step 13, a composite oxide of lithium and a first transition metal with a layered rock-salt-type crystal structure can be synthesized. At this point, the main group elements and fluorine contained in the starting materials form a solid solution in the composite oxide. However, some of the main group elements may sometimes segregate onto the surface of the composite oxide.

[0291] Furthermore, pre-synthesized composite oxide particles containing lithium, cobalt, fluorine, and magnesium can be used as starting materials. In this case, steps 12 and 13 can be omitted. For example, lithium cobalt oxide particles (trade name: C-20F) manufactured by Nippon Chemical Industries, Ltd. can be used as one of the starting materials. These lithium cobalt oxide particles have a particle size of approximately 20 μm and contain fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus from the surface to the region that can be analyzed by XPS.

[0292] <Step 14: Cover with the second transition metal>

[0293] Next, the composite oxide of lithium and the first transition metal is cooled to room temperature. Then, the surface of the composite oxide particles of lithium and the first transition metal is covered with a material containing a second transition metal. In this formation method example, the sol-gel method is used.

[0294] First, a second transition metal alkoxide dissolved in an alcohol is mixed with a composite oxide particle of lithium and a first transition metal.

[0295] For example, when using titanium as the second transition metal, TTIP can be used as an alkoxide of the second transition metal. Furthermore, isopropanol can be used as an alcohol, for example.

[0296] Next, the mixture is stirred in an atmosphere containing water vapor. For example, a magnetic stirrer can be used. The stirring time is sufficient for the water in the atmosphere to undergo sufficient hydrolysis and condensation reaction with TTIP; for example, stirring can be carried out for 4 hours at 25°C under 90% RH (relative humidity).

[0297] As described above, by reacting water with TTIP in an atmosphere, the sol-gel reaction can proceed more slowly compared to adding water as a liquid. Furthermore, by reacting the titanium alkoxide with water at room temperature, for example, compared to heating at a temperature higher than the boiling point of the alcohol in the solvent, the sol-gel reaction can proceed more slowly. By slowing down the progress of the sol-gel reaction, a titanium-containing coating layer of uniform thickness and of higher quality can be formed.

[0298] After the above treatment, the precipitate is collected from the mixture. Collection methods include filtration, centrifugation, and evaporation. In this embodiment, the precipitate is collected by filtration. Filter paper is used in the filtration, and the residue is washed with an alcohol identical to the solvent in which the titanium alkoxide is dissolved.

[0299] Next, the collected residue is dried. In this embodiment, it is vacuum dried at 70°C for 1 hour.

[0300] <Step 15: Second Heating>

[0301] Next, the composite oxide particles covered by the material containing the second transition metal, formed in step 14, are heated. This step is sometimes referred to as the second heating. During heating, the holding time within a specified temperature range is preferably 50 hours or less, more preferably 2 hours or more and 10 hours or less, and even more preferably 1 hour or more and 3 hours or less. When the heating time is too short, there is a concern that segregation of main group elements may not occur; however, when the heating time is too long, there is a concern that the diffusion of the second transition metal may progress too much and the desired second region 102 may not be formed.

[0302] The specified temperature is preferably 500°C or higher and 1200°C or lower, more preferably 800°C or higher and 1000°C or lower. When the specified temperature is too low, there is a concern that segregation of main group elements and the second transition metal may not occur. When the specified temperature is too high, there are concerns that the first transition metal in the composite oxide particles may be reduced, causing the composite oxide particles to decompose; and that the layered structure of lithium and the first transition metal in the composite oxide particles may not be maintained.

[0303] In this embodiment, the specified temperature is 800°C, the holding time is 2 hours, the heating rate is 200°C / h, and the flow rate of the dry air is 10L / min.

[0304] By performing the heating in step 15, the composite oxide of lithium and the first transition metal is topologically derived with the oxide of the second transition metal covering the composite oxide, namely the first region 101 and the second region 102.

[0305] By heating in step 15, the main group elements that form a solid solution in the composite oxide particles of lithium and the first transition metal are unevenly distributed on the surface to form a solid solution, i.e., main group element segregation to form compounds of main group elements, thus forming the third region 103. At this time, the compounds of main group elements are formed by heteroepitaxial growth from the second region 102. That is, the second region 102 and the third region 103 are topologically derived.

[0306] Because the second region 102 and the third region 103 contain crystals with substantially consistent orientation and a stable bond with the first region 101, changes in the crystal structure of the first region 101 due to charging and discharging can be effectively suppressed when the positive electrode active material 100 is used in a secondary battery. Even if lithium is deintercalated from the first region 101 during charging, the surface portion with a stable bond can suppress the deintercalation of first transition metals such as cobalt and oxygen from the first region 101. Furthermore, the region in contact with the electrolyte can use a chemically stable material. Thus, a secondary battery with excellent cycle characteristics can be provided.

[0307] Note that the first region 101 and the second region 102 do not necessarily need to be entirely topologically derived; it is sufficient that they are partially topologically derived. Similarly, the second region 102 and the third region 103 do not necessarily need to be entirely topologically derived; it is sufficient that they are partially topologically derived.

[0308] When the compound containing the main group element 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.

[0309] In addition, fluorine contained in the starting material promotes the segregation of main group elements.

[0310] In this way, in the method for forming a positive electrode active material according to one embodiment of the present invention, a third region 103 is formed by heating after covering the element that forms the second region 102, thereby forming two regions on the surface of the positive electrode active material 100. That is, normally two covering steps are required to form two regions on the surface, but in the method for forming a positive electrode active material according to one embodiment of the present invention, only one covering step (sol-gel step) is required, thus making it a highly productive forming method.

[0311] <Step 16: Cooling>

[0312] Next, the particles heated in step 15 are cooled to room temperature. The cooling time is preferably relatively long to facilitate topological derivation. For example, the cooling time from the holding temperature to room temperature is preferably longer than the heating time, specifically, 10 hours or more and 50 hours or less.

[0313] <Step 17: Collection>

[0314] Next, the cooled particles are collected. Preferably, the particles are sieved. Through the above steps, a positive electrode active material 100 comprising a first region 101, a second region 102, and a third region 103 can be formed.

[0315] This implementation method can be appropriately combined with other implementation methods.

[0316] (Implementation Method 2)

[0317] In this embodiment, an example of a material that can be used in a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. In this embodiment, a secondary battery in which the positive electrode, negative electrode, and electrolyte are surrounded by an outer packaging body will be used as an example.

[0318] [positive electrode]

[0319] The positive electrode includes the positive electrode active material layer and the positive electrode current collector.

[0320] <Positive Electrode Active Material Layer>

[0321] The positive electrode active material layer contains at least the positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer may also contain other substances such as a coating film, conductive additives, or adhesives on the surface of the active material.

[0322] The positive electrode active material 100 described in the above embodiments can be used as the positive electrode active material. By using the positive electrode active material 100 described in the above embodiments, a secondary battery with high capacity and excellent cycle characteristics can be realized.

[0323] Carbon materials, metallic materials, or conductive ceramic materials can be used as conductive additives. Furthermore, fibrous materials can also be used. The proportion of the conductive additive in the total amount of the active material layer is preferably 1 wt% or more and 10 wt% or less, more preferably 1 wt% or more and 5 wt% or less.

[0324] By utilizing conductive additives, a conductive network can be formed within the active material layer. These additives also maintain the conductive pathways between the positive electrode active materials. Furthermore, by adding conductive additives to the active material layer, an active material layer with high electrical conductivity can be achieved.

[0325] As conductive additives, examples include natural graphite, artificial graphite such as mesophase carbon microspheres, and carbon fibers. For carbon fibers, examples include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Carbon nanofibers or carbon nanotubes can also be used. For example, carbon nanotubes can be manufactured using methods such as vapor phase growth. As conductive additives, examples include carbon materials such as carbon black (acetylene black (AB), etc.), graphite (lead black) particles, graphene, or fullerenes. Furthermore, examples include metal powders or fibers of copper, nickel, aluminum, silver, gold, etc., and conductive ceramic materials.

[0326] In addition, graphene compounds can also be used as conductive additives.

[0327] Graphene compounds sometimes possess excellent electrical properties such as high conductivity, as well as excellent physical properties such as high flexibility and high mechanical strength. Furthermore, graphene compounds have a planar shape. Graphene compounds can form surface contacts with low contact resistance. Graphene compounds sometimes exhibit very high conductivity even when thin, thus allowing conductive pathways to be formed efficiently in small amounts within the active material layer. Therefore, using graphene compounds as conductive additives increases the contact area between the active material and the conductive additive, which is preferred. Preferably, by utilizing a spray drying apparatus, the graphene compound used as a conductive additive as a coating film can be formed in a manner that covers the entire surface of the active material. Furthermore, resistance can be reduced, which is also preferred. Here, it is particularly preferred to use graphene, multilayer graphene, or RGO as the graphene compound. Here, RGO refers, for example, to a compound obtained by reducing graphene oxide (GO).

[0328] When using active materials with small particle sizes, such as those with a particle size of less than 1 μm, the specific surface area of ​​the active material is large, thus requiring more conductive paths connecting the active materials. Therefore, the amount of conductive additive tends to increase, resulting in a relative decrease in the content of the active material. When the content of the active material decreases, the capacity of the secondary battery also decreases. In this case, since it is not necessary to reduce the content of the active material, graphene compounds that can efficiently form conductive paths even in small amounts are particularly preferred as conductive additives.

[0329] The following is an example illustrating the cross-sectional structure of the active material layer 200 containing a graphene compound as a conductive additive.

[0330] Figure 7AThis is a longitudinal cross-sectional view of the active material layer 200. The active material layer 200 includes granular positive electrode active material 100, graphene compound 201 used as a conductive additive, and a binder (not shown). Here, as the graphene compound 201, graphene or multilayer graphene can be used, for example. Furthermore, the graphene compound 201 is preferably in a sheet-like form. The graphene compound 201 can be formed into a sheet by partially overlapping multiple multilayer graphene or (and) multiple monolayer graphene.

[0331] In the longitudinal section of the active material layer 200, such as Figure 7B As shown, the sheet-like graphene compound 201 is dispersed approximately uniformly within the active material layer 200. Figure 7B Although graphene compound 201 is schematically represented by a thick line, it is actually a thin film with a single or multiple layers of carbon molecules. Since multiple graphene compounds 201 are formed either by covering a portion of multiple particulate positive electrode active materials 100 or by attaching to the surface of multiple particulate positive electrode active materials 100, the graphene compounds 201 and the positive electrode active materials 100 form surface contact.

[0332] Here, by bonding multiple graphene compounds together, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound mesh or graphene network) can be formed. When the graphene network covers the active material, it can be used as a binder to bond the compounds together. Therefore, the amount of binder can be reduced or eliminated, thereby increasing the proportion of active material in the electrode volume or weight. In other words, the capacity of the secondary battery can be increased.

[0333] Preferably, graphene oxide is used as the graphene compound 201. This graphene oxide is mixed with an active material to form a layer that will become the active material layer 200, and then reduced. By using highly dispersible graphene oxide in a polar solvent in the formation of the graphene compound 201, the graphene compound 201 can be dispersed substantially uniformly in the active material layer 200. The solvent is evaporated from the dispersion medium containing the uniformly dispersed graphene oxide, and the graphene oxide is reduced. Therefore, the graphene compounds 201 remaining in the active material layer 200 partially overlap each other, dispersing in a surface-contact manner, thereby forming a three-dimensional conductive path. Furthermore, the reduction of graphene oxide can also be carried out, for example, by heat treatment or by using a reducing agent.

[0334] Therefore, unlike granular conductive additives such as acetylene black that form point contacts with the active material, graphene compound 201 can form surface contacts with low contact resistance. Thus, the conductivity between the granular positive electrode active material 100 and graphene compound 201 can be improved with less graphene compound 201 than with typical conductive additives. Therefore, the proportion of granular positive electrode active material 100 in the active material layer 200 can be increased. This, in turn, increases the discharge capacity of the secondary battery.

[0335] Furthermore, by pre-treating with a spray drying device, graphene compounds can be used to cover the entire surface of the active material. Then, when forming the positive electrode active material layer, graphene compounds can be further added to optimize the conductive pathways between the active materials.

[0336] Preferred adhesives include, for example, styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Fluororubber can also be used as an adhesive.

[0337] Furthermore, water-soluble polymers are preferably used as adhesives. Examples of water-soluble polymers include polysaccharides. Among polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch, can be used. More preferably, these water-soluble polymers and the aforementioned rubber material are used in combination.

[0338] Alternatively, materials such as polystyrene, polymethyl methacrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylene propylene diene monomer (EPDM), polyvinyl acetate, and nitrocellulose are preferred as adhesives.

[0339] As an adhesive, multiple of the above materials can also be used in combination.

[0340] For example, materials with particularly high viscosity-modifying properties can be used in combination with other materials. For instance, while materials like rubber have high adhesive strength and high elasticity, viscosity can sometimes be difficult to adjust when mixed in a solvent. In such cases, it is preferable to mix them with materials that have particularly high viscosity-modifying properties. Water-soluble polymers can be used as examples of materials with particularly high viscosity-modifying properties. Furthermore, polysaccharides mentioned above can be used as water-soluble polymers with particularly good viscosity-modifying properties, such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, and starch.

[0341] Note that cellulose derivatives such as carboxymethyl cellulose, for example, by being converted into sodium or ammonium salts of carboxymethyl cellulose, have increased solubility and thus readily function as viscosity modifiers. Due to the increased solubility, the dispersibility of the active material with other components can be improved when forming the electrode slurry. In this specification, cellulose and cellulose derivatives used as binders for electrodes include their salts.

[0342] By dissolving water-soluble polymers in water to stabilize their viscosity, active materials and other materials used as binders, such as styrene-butadiene rubber, can be stably dispersed in aqueous solutions. Because water-soluble polymers possess functional groups, they are expected to readily and stably adhere to the surface of active materials. Cellulose derivatives, such as carboxymethyl cellulose, often possess functional groups such as hydroxyl and carboxyl groups. Due to these functional groups, the polymers are expected to interact and extensively cover the surface of active materials.

[0343] When an adhesive film is formed covering or contacting the surface of an active material, it is also desirable for it to function as a passivation film to suppress electrolyte decomposition. Here, the passivation film is a film with no conductivity or extremely low conductivity; for example, when a passivation film is formed on the surface of the active material, it can suppress electrolyte decomposition at the battery reaction potential. More preferably, the passivation film can transport lithium ions while suppressing conductivity.

[0344] Positive current collector

[0345] As the positive electrode current collector, highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, and their alloys can be used. Furthermore, the material used for the positive electrode current collector is preferably one that does not dissolve due to the potential of the positive electrode. Additionally, aluminum alloys with added elements to improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. Furthermore, metal elements that react with silicon to form silicides can also be used. Examples of metal elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can appropriately have shapes such as foil, plate (sheet), mesh, perforated metal mesh, or drawn metal mesh. The thickness of the current collector is preferably 5 μm or more and 30 μm or less.

[0346] [negative electrode]

[0347] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain conductive additives and binders.

[0348] <Negative Electrode Active Material>

[0349] As a negative electrode active material, alloy materials or carbon materials can be used, for example.

[0350] As the negative electrode active material, elements capable of undergoing charge-discharge reactions through alloying / dealloying with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a higher capacity than carbon, especially silicon, which has a theoretical capacity of 4200 mAh / g. Therefore, silicon is preferred for use as the negative electrode active material. Furthermore, compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Elements that can undergo charge-discharge reactions through alloying / dealloying with lithium, and compounds containing such elements, are sometimes referred to as alloy materials.

[0351] In this specification and other materials, SiO refers to silicon monoxide, for example. Alternatively, SiO may also be represented as SiO₂. x Here, x preferably represents a value near 1. For example, x is preferably 0.2 or higher and 1.5 or lower, and more preferably 0.3 or higher and 1.2 or lower.

[0352] As carbon-based materials, graphite, easily graphitized carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. can be used.

[0353] Examples of graphite include synthetic graphite and natural graphite. Examples of synthetic graphite include mesophase carbon microspheres (MCMB), coke-based synthetic graphite, and pitch-based synthetic graphite. Spherical graphite with a spherical shape can be used as synthetic graphite. For example, MCMB sometimes has a spherical shape, which is preferred. Furthermore, MCMB is relatively easy to reduce its surface area, so it is sometimes preferred. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0354] When lithium ions are intercalated in graphite (during the formation of lithium-graphite intercalation compounds), graphite exhibits a low potential similar to that of lithium metal (above 0.05V and below 0.3V vs. Li / Li). + Therefore, lithium-ion secondary batteries can exhibit high operating voltages. Graphite also has the following advantages: larger capacity per unit volume; smaller volume expansion; lower cost; and higher safety compared to lithium metal, making it a preferred choice.

[0355] In addition, oxides such as titanium dioxide (TiO2) and lithium titanium oxide (Li4Ti5O) can be used as negative electrode active materials. 12 ), lithium-graphite intercalation compounds (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc.

[0356] Furthermore, Li3N-type structures containing lithium and transition metal nitrides can be used as negative electrode active materials. 3-x M x N (M = Co, Ni, Cu). For example, Li 2.6 Co 0.4 N3 exhibits a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm³). 3 Therefore, it is the preferred option.

[0357] When lithium- and transition metal-containing nitrides are used as negative electrode active materials, lithium ions are present in the negative electrode active material. Therefore, this negative electrode active material can be combined with materials that do not contain lithium ions, such as V₂O₅ and Cr₃O₈, which are used as positive electrode active materials, making this a preferred method. Note that when lithium-ion-containing materials are used as positive electrode active materials, lithium ions can be pre-desorbed from the positive electrode active material, and lithium- and transition metal-containing nitrides can also be used as negative electrode active materials.

[0358] Furthermore, materials that induce the conversion reaction can also be used as negative electrode active materials. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as negative electrode active materials. Other examples of materials that induce the conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS. 0.89 Sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.

[0359] The conductive additives and binders that may be included in the negative electrode active material layer can be the same materials that may be included in the positive electrode active material layer.

[0360] <Negative Electrode Current Collector>

[0361] The same material as the positive electrode current collector can be used as the negative electrode current collector. Furthermore, it is preferable to use a material that does not alloy with carrier ions such as lithium as the negative electrode current collector.

[0362] Electrolyte

[0363] The electrolyte comprises a solvent and an electrolyte. Preferably, aprotic organic solvents are used as the solvent for the electrolyte, such as ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, vinyl chloride carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethyl glycol ether (DME), dimethyl sulfoxide, diethyl ether, methyl diethylene glycol dimethyl ether, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sulfonyl sulfone, sulfonyl lactone, etc., or two or more of the above can be used in any combination and ratio.

[0364] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room temperature molten salts) as the solvent for the electrolyte, even if the internal temperature of the secondary battery rises due to internal short circuits, overcharging, etc., it can prevent the secondary battery from rupturing or catching fire. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, or aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methylide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0365] In addition, as electrolytes dissolved in the above solvents, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B can be used. 10 Cl 10 Li2B 12 Cl 12 One of the following lithium salts: LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc., or two or more of the above can be used in any combination and ratio.

[0366] As the electrolyte for secondary batteries, it is preferable to use a high-purity electrolyte with low content of particulate dust or elements other than the constituent elements of the electrolyte (hereinafter referred to as "impurities"). Specifically, the proportion of impurities in the weight of the electrolyte is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0367] In addition, additives such as vinylene carbonate, propanesulfonate lactone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), or dinitrile compounds such as succinate and adiponitrile can be added to the electrolyte. The concentration of the added material can be set, for example, to be more than 0.1 wt% and less than 5 wt% in the total solvent.

[0368] Alternatively, polymer gel electrolytes in which the polymer has been swollen by an electrolyte solution can also be used.

[0369] Furthermore, by using a polymer gel electrolyte, safety against leakage is improved. Moreover, the secondary device can be made thinner and lighter.

[0370] As a gelling polymer, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polyoxypropylene gels, fluoropolymer gels, etc. can be used.

[0371] As polymers, polymers having a polyoxyalkylene structure, such as polyethylene oxide (PEO), PVDF, and polyacrylonitrile, as well as copolymers containing these, can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the resulting polymer can also have a porous shape.

[0372] Furthermore, solid electrolytes containing inorganic materials such as sulfides or oxides, or solid electrolytes containing polymeric materials such as PEO (polyethylene oxide), can be used instead of liquid electrolytes. When using solid electrolytes, there is no need to install separators or spacers. In addition, since the entire battery can be solidified, there is no concern about leakage, thus significantly improving safety.

[0373] [Isolation]

[0374] Furthermore, the secondary battery preferably includes a separator. As the separator, materials such as paper, nonwoven fabric, glass fiber, ceramic, or synthetic fibers containing nylon (polyamide), vinylon (polyvinyl alcohol fibers), polyester, acrylic resin, polyolefin, or polyurethane can be used. Preferably, the separator is processed into a bag shape and configured to surround either the positive or negative electrode.

[0375] The separator can have a multilayer structure. For example, ceramic materials, fluorinated materials, polyamide materials, or mixtures thereof can be coated onto organic materials such as polypropylene and polyethylene. Examples of ceramic materials include alumina particles and silica particles. Examples of fluorinated materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aromatic polyamides (meta-aromatic polyamides and para-aromatic polyamides).

[0376] Coating with ceramic materials can improve oxidation resistance, thereby suppressing the degradation of the separator during high-voltage charging and discharging, and thus improving the reliability of the secondary battery. Coating with fluorine-based materials facilitates a tighter connection between the separator and the electrodes, thereby improving output characteristics. Coating with polyamide materials (especially aromatic polyamides) can improve heat resistance, thereby improving the safety of the secondary battery.

[0377] For example, a mixture of alumina and aromatic polyamide can be coated on both sides of the polypropylene film. Alternatively, the side of the polypropylene film in contact with the positive electrode can be coated with a mixture of alumina and aromatic polyamide, while the side in contact with the negative electrode can be coated with a fluorinated material.

[0378] By employing a multi-layered separator, the safety of the secondary battery can be ensured even if the total thickness of the separator is small, thus increasing the capacity per unit volume of the secondary battery.

[0379] [Outer Packaging]

[0380] The outer packaging of a secondary battery can be made of materials such as metals like aluminum and resins. Alternatively, a thin-film outer packaging can be used. For example, a three-layer film can be used: a flexible metal film such as aluminum, stainless steel, copper, or nickel is placed on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide; and an insulating synthetic resin film such as polyamide or polyester resin can be placed on this metal film as the outer surface of the outer packaging.

[0381] [Charging and discharging method]

[0382] The charging and discharging of a secondary battery can be performed, for example, as described below.

[0383] CC Charging

[0384] First, let's explain CC charging as a charging method. CC charging refers to a charging method in which a constant current flows through the secondary battery throughout the entire charging period, and charging stops when the voltage of the secondary battery reaches a predetermined voltage. For example... Figure 8A As shown, the secondary battery is assumed to be an equivalent circuit with internal resistance R and secondary battery capacity C. In this case, the secondary battery voltage V B It is the voltage V applied to the internal resistor R. R and the voltage V applied to the secondary battery capacity C C The sum of .

[0385] During CC charging, such as Figure 8A As shown, the switch is turned on, and a constant current I flows through the secondary battery. During this period, because the current I is constant, the voltage V applied to the internal resistor R is... R According to V R =R×I, which is constant according to Ohm's law. On the other hand, the voltage V applied to the secondary battery's capacity C is... C It increases over time. Therefore, the secondary battery voltage V B It rises over time.

[0386] Furthermore, when the secondary battery voltage V B When the voltage reaches the specified level, such as 4.3V, charging stops. When CC charging stops, as... Figure 8B As shown, the switch is closed, and the current I = 0. Therefore, the voltage V applied to the internal resistor R is... RIt becomes 0V. Therefore, the secondary battery voltage V B The drop is equivalent to the portion of the voltage across the internal resistor R that no longer decreases.

[0387] Figure 8C This shows the secondary battery voltage V during CC charging and after CC charging is stopped. B An example related to charging current. (By...) Figure 8C It can be seen that the secondary battery voltage V rises during CC charging. B It decreases slightly after CC charging stops.

[0388] CCCV Charging

[0389] Next, a different charging method, namely CCCV charging, will be explained. CCCV charging refers to first performing CC charging to charge to a specified voltage, and then performing CV (constant voltage) charging to charge until the current flowing through it decreases. Specifically, it is a charging method that charges to the point where the termination current value is reached.

[0390] During CC charging, such as Figure 9A As shown, the constant current switch is on, and the constant voltage switch is off, thus a constant current I flows through the secondary battery. During this period, because the current I is constant, the voltage V applied to the internal resistor R is constant. R According to V R =R×I, which is constant according to Ohm's law. On the other hand, the voltage V applied to the secondary battery's capacity C is... C It increases over time. Therefore, the secondary battery voltage V B It rises over time.

[0391] Furthermore, when the secondary battery voltage V B When the voltage reaches a specified level, such as 4.3V, the system switches from CC charging to CV charging. During CV charging, if... Figure 9B As shown, the constant current switch is on, and the constant voltage switch is off, therefore the secondary battery voltage V B It is constant. On the other hand, the voltage V applied to the secondary battery capacity C is constant. C It rises over time. Because it satisfies V. B =V R +V C Therefore, the voltage V applied to the internal resistor R R It decreases over time. This decreases with the voltage V applied to the internal resistor R. R The current I flowing through the secondary battery decreases according to V. R =R×I, which decreases due to Ohm's law.

[0392] Furthermore, charging stops when the current I flowing through the secondary battery reaches a specified current, for example, equivalent to a current of 0.01C. When CCCV charging stops, as shown... Figure 9C As shown, all switches are closed, resulting in a current I = 0. Therefore, the voltage V applied to the internal resistor R is... R It becomes 0V. However, because the voltage V applied to the internal resistor R is sufficiently reduced by charging through CV. R Therefore, even if the voltage across the internal resistor R no longer decreases, the secondary battery voltage V B It also hardly decreased.

[0393] Figure 9D This shows the secondary battery voltage V during CCCV charging and after CCCV charging is stopped. B An example related to charging current. (By...) Figure 9D It can be seen that the secondary battery voltage V B Even after CCCV charging is stopped, it hardly decreases.

[0394] CC Charging

[0395] Next, one of the discharge methods, CC discharge, will be explained. CC discharge refers to the discharge of a constant current from the secondary battery throughout the entire discharge period, while the secondary battery voltage V remains constant. B A discharge method that stops discharging when the voltage reaches a specified level, such as 2.5V.

[0396] Figure 10 This shows the secondary battery voltage V during CC discharge. B An example related to discharge current. From Figure 10 It can be seen that the secondary battery voltage V B It decreases as the discharge progresses.

[0397] Here, we will explain the discharge rate and charge rate. The discharge rate refers to the ratio of the discharge current to the battery capacity, and is expressed in units of C. In a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). When discharging at a current of 2X (A), it can be said to be discharging at 2C, and when discharging at a current of X / 5 (A), it can be said to be discharging at 0.2C. Similarly, the charge rate is the same; when charging at a current of 2X (A), it can be said to be charging at 2C, and when charging at a current of X / 5 (A), it can be said to be charging at 0.2C.

[0398] (Implementation Method 3)

[0399] In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the above embodiments will be described. The materials used in the secondary battery described in this embodiment can be found in the description of the above embodiments.

[0400] [Coin-type rechargeable battery]

[0401] First, let's illustrate an example of a coin-type secondary battery. Figure 11A This is an image of a coin-shaped (single-layer flat) secondary battery. Figure 11B This is its cross-sectional view.

[0402] In the coin-type secondary battery 300, the positive electrode container 301, which also serves as the positive terminal, and the negative electrode container 302, which also serves as the negative terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 disposed in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 disposed in contact with it.

[0403] The active material layers included in the positive electrode 304 and negative electrode 307 of the coin-type secondary battery 300 can be formed on only one surface of the positive electrode and the negative electrode.

[0404] As the positive electrode container 301 and the negative electrode container 302, metals such as nickel, aluminum, and titanium, alloys thereof, or alloys thereof with other metals (e.g., stainless steel) that are resistant to electrolyte corrosion can be used. Furthermore, to prevent corrosion caused by the electrolyte, the positive electrode container 301 and the negative electrode container 302 are preferably covered with nickel or aluminum. The positive electrode container 301 is electrically connected to the positive electrode 304, and the negative electrode container 302 is electrically connected to the negative electrode 307.

[0405] By impregnating these negative electrode 307, positive electrode 304, and separator 310 into the electrolyte, such as Figure 11B As shown, a coin-shaped secondary battery 300 is manufactured by stacking a positive electrode 304, an insulator 310, a negative electrode 307, and a negative electrode can 302 in sequence below a positive electrode can 301, and pressing the positive electrode can 301 and the negative electrode can 302 together with a gasket 303.

[0406] By using the positive electrode active material described in the above embodiments in the positive electrode 304, a coin-type secondary battery 300 with high capacity and excellent cycle characteristics can be realized.

[0407] Here, refer to Figure 11CThis describes how current flows when charging a secondary battery. When a lithium-ion secondary battery is considered as a closed circuit, the direction of lithium-ion migration is the same as the direction of current flow. Note that in lithium-ion secondary batteries, since the anode and cathode, oxidation and reduction reactions are reversed depending on whether the battery is charging or discharging, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Therefore, in this specification, even when charging, discharging, supplying a reverse pulse current, and supplying a charging current, the positive electrode is referred to as the "positive electrode" or "+ electrode," and the negative electrode is referred to as the "negative electrode" or "- electrode." If the terms anode and cathode related to oxidation and reduction reactions are used, the anode and cathode would be reversed during charging and discharging, which could cause confusion. Therefore, the terms anode and cathode are not used in this specification. When the terms anode and cathode are used, it is clearly indicated whether it is during charging or discharging, and it is shown whether it corresponds to the positive electrode (+ electrode) or the negative electrode (- electrode).

[0408] Figure 11C The two terminals shown are connected to a charger to charge the secondary battery 300. As the secondary battery 300 is charged, the potential difference between the electrodes increases.

[0409] Cylindrical secondary battery

[0410] Next, refer to Figures 12A to 12D An example of a cylindrical secondary battery will be given. For example... Figure 12A As shown, the cylindrical secondary battery 600 has a positive electrode cover (battery cover) 601 on the top surface and battery canisters (outer canisters) 602 on the sides and bottom surface. The positive electrode cover and the battery canisters (outer canisters) 602 are insulated from each other by a gasket (insulating gasket) 610.

[0411] Figure 12B This is a schematic cross-section diagram of a cylindrical secondary battery. A battery element is disposed inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound around an insulator 605. Although not shown, the battery element is wound around a central pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of metals such as nickel, aluminum, and titanium, alloys thereof, or alloys of these metals with other metals (e.g., stainless steel), which are resistant to electrolyte corrosion. Furthermore, to prevent corrosion caused by the electrolyte, the battery can 602 is preferably covered with nickel or aluminum. Inside the battery can 602, the battery element, consisting of the wound positive electrode, negative electrode, and insulator, is held between a pair of opposing insulating plates 608 and 609. Furthermore, a non-aqueous electrolyte (not shown) is injected into the interior of the battery can 602 where the battery element is disposed. As a non-aqueous electrolyte, the same electrolyte as that used in coin-type secondary batteries can be used.

[0412] Because the positive and negative electrodes of the cylindrical secondary battery are wound, the active material is preferably formed on both surfaces of the current collector. The positive electrode 604 is connected to the positive terminal (positive current collector wire) 603, while the negative electrode 606 is connected to the negative terminal (negative current collector wire) 607. Both the positive terminal 603 and the negative terminal 607 can be made of metal materials such as aluminum. The positive terminal 603 is resistor-welded to the safety valve mechanism 612, and the negative terminal 607 is resistor-welded to the bottom of the battery canister 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a positive temperature coefficient (PTC) element 611. When the internal pressure of the battery rises above a predetermined threshold, the safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604. Furthermore, the PTC element 611 is a heat-sensitive resistor whose resistance increases with temperature, and the increased resistance limits the current to prevent abnormal heating. As the PTC element, a semiconductor ceramic such as barium titanate (BaTiO3) can be used.

[0413] In addition, such as Figure 12C As shown, multiple secondary batteries 600 can also be sandwiched between conductive plates 613 and 614 to form a module 615. The multiple secondary batteries 600 can be connected in parallel, in series, or in parallel followed by series connection. By constructing a module 615 including multiple secondary batteries 600, a greater amount of power can be extracted.

[0414] Figure 12D This is a top view of module 615. For clarity, the conductive plate 613 is represented by dashed lines. Figure 12D As shown, module 615 may include wires 616 that electrically connect multiple secondary batteries 600. A conductive plate 613 may be disposed on the wires 616 in a manner overlapping the wires 616. Furthermore, a temperature control device 617 may be included among the multiple secondary batteries 600. The temperature control device 617 can cool a secondary battery 600 when it is overheated and heat it when it is undercooled. Therefore, the performance of module 615 is less susceptible to the influence of external temperature.

[0415] By using the positive electrode active material described in the above embodiments in the positive electrode 604, a cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be realized.

[0416] [Example of a secondary battery structure]

[0417] Reference Figures 13A to 16 Other structural examples of secondary batteries are illustrated.

[0418] Figure 13A and Figure 13BThis is an external view of the secondary battery. The secondary battery 913 includes a circuit board 900 and the secondary battery 913 itself. A label 910 is affixed to the secondary battery 913. Furthermore, as... Figure 13B As shown, the secondary battery also includes terminal 951, terminal 952, antenna 914, and antenna 915.

[0419] The circuit board 900 includes terminals 911 and circuitry 912. Terminals 911 are connected to terminals 951, 952, antennas 914 and 915, and circuitry 912. Alternatively, multiple terminals 911 can be provided, which can be used as control signal input terminals, power supply terminals, etc.

[0420] Circuit 912 can also be disposed on the back of circuit board 900. Furthermore, the shapes of antennas 914 and 915 are not limited to coils; for example, they can also be wire-shaped or plate-shaped. Additionally, planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, or dielectric antennas can be used. Alternatively, antenna 914 or antenna 915 can also be a planar conductor. This planar conductor can also be used as one of the conductors for electric field coupling. In other words, antenna 914 or antenna 915 can also be used as one of the two conductors in a capacitor. Thus, not only electromagnetic and magnetic fields can be utilized, but also electric fields can be used to exchange power.

[0421] The linewidth of antenna 914 is preferably greater than that of antenna 915. This increases the electrical force on antenna 914.

[0422] The secondary battery includes a layer 916 between the antenna 914 and antenna 915 and the secondary battery 913. The layer 916, for example, has the function of shielding electromagnetic fields from the secondary battery 913. As the layer 916, a magnetic material can be used, for example.

[0423] The structure of secondary batteries is not limited to Figure 13A and Figure 13B The structure shown.

[0424] For example, such as Figure 14A-1 and Figure 14A-2 As shown, it can also be found in Figure 13A and Figure 13B Antennas are respectively mounted on a pair of opposite surfaces of the secondary battery 913 shown. Figure 14A-1 This is a view showing the appearance of one side of one of the above pair of surfaces. Figure 14A-2 This is a view showing the appearance of one side of the other surface of the aforementioned pair of surfaces. Furthermore, with... Figure 13A and Figure 13B The same parts of the secondary battery shown can be appropriately referenced. Figure 13A and Figure 13B Description of the secondary battery shown.

[0425] like Figure 14A-1 As shown, an antenna 914 is disposed on one of the two surfaces of the secondary battery 913, with a layer 916 sandwiched between them. Figure 14A-2 As shown, an antenna 918 is disposed on the other of a pair of surfaces of the secondary battery 913, sandwiched between layers 917. Layer 917, for example, has the function of shielding electromagnetic fields from the secondary battery 913. A magnetic material can be used as layer 917, for example.

[0426] By adopting the above structure, the dimensions of both antenna 914 and antenna 918 can be increased. Antenna 918, for example, has the function of data communication with external devices. As antenna 918, for example, an antenna with a shape applicable to antenna 914 can be used. As a communication method between the secondary battery utilizing antenna 918 and other devices, a response method such as NFC that can be used between the secondary battery and other devices can be used.

[0427] Or, such as Figure 14B-1 As shown, it can also be found in Figure 13A and Figure 13B A display device 920 is provided on the secondary battery 913 shown. The display device 920 is electrically connected to the terminal 911. Alternatively, the label 910 may not be attached to the portion where the display device 920 is provided. Furthermore, with... Figure 13A and Figure 13B The same parts of the secondary battery shown can be appropriately referenced. Figure 13A and Figure 13B Description of the secondary battery shown.

[0428] The display device 920 may display, for example, an image indicating whether charging is in progress, or an image indicating the amount of power stored. The display device 920 may be, for example, electronic paper, a liquid crystal display, or an electroluminescent (EL) display. For example, using electronic paper can reduce the power consumption of the display device 920.

[0429] Or, such as Figure 14B-2 As shown, it can also be found in Figure 13A and Figure 13B A sensor 921 is installed in the secondary battery 913 shown. The sensor 921 is electrically connected to terminal 911 via terminal 922. Furthermore, with... Figure 13A and Figure 13B The same parts of the secondary battery shown can be appropriately referenced. Figure 13A and Figure 13B Description of the secondary battery shown.

[0430] Sensor 921 may, for example, have the function of measuring factors such as: displacement, position, velocity, acceleration, angular velocity, number of rotations, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electrical power, radiation, flow rate, humidity, slope, vibration, odor, or infrared radiation. By setting sensor 921, for example, data (temperature, etc.) showing the environment in which the secondary battery is set can be detected and stored in the memory of circuit 912.

[0431] Furthermore, refer to Figure 15A and Figure 15B as well as Figure 16 The structure of the secondary battery 913 is illustrated using an example.

[0432] Figure 15A The secondary battery 913 shown includes a wound body 950 with terminals 951 and 952 inside a frame 930. The wound body 950 is immersed in electrolyte inside the frame 930. Terminal 952 contacts the frame 930, while terminal 951 does not contact the frame 930 due to insulating material. Note that, for convenience, although... Figure 15A The diagram shows a separate frame 930; however, the winding body 950 is actually covered by the frame 930, and terminals 951 and 952 extend to the outside of the frame 930. The frame 930 can be made of metal (e.g., aluminum) or resin.

[0433] In addition, such as Figure 15B As shown, multiple materials can also be used to form Figure 15A The frame 930 is shown. For example, in... Figure 15B In the secondary battery 913 shown, the frame 930a and the frame 930b are attached together, and a winding body 950 is provided in the area surrounded by the frame 930a and the frame 930b.

[0434] As the frame 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin to form the surface of the antenna, the electric field shielding caused by the secondary battery 913 can be suppressed. Furthermore, if the electric field shielding caused by the frame 930a is small, an antenna such as antenna 914 or antenna 915 can be installed inside the frame 930a. As the frame 930b, for example, a metal material can be used.

[0435] Furthermore, Figure 16 The structure of the wound body 950 is shown. The wound body 950 includes a negative electrode 931, a positive electrode 932, and an insulator 933. The wound body 950 is formed by sandwiching the insulator 933, overlapping the negative electrode 931 and the positive electrode 932 to form a laminate, and then winding the laminate. Alternatively, multiple laminates of negative electrode 931, positive electrode 932, and insulator 933 can be further stacked.

[0436] The negative terminal 931 is connected to one of terminals 951 and 952. Figure 13A and Figure 13B Terminal 911 is shown as the connection point. The positive terminal 932 is connected to the other terminal via terminal 951 and terminal 952. Figure 13A and Figure 13B The terminal 911 shown is connected.

[0437] By using the positive electrode active material described in the above embodiments in the positive electrode 932, a secondary battery 913 with high capacity and excellent cycle characteristics can be realized.

[0438] [Laminated secondary battery]

[0439] Next, refer to Figures 17A to 23B An example of a laminated secondary battery is given. When a flexible laminated secondary battery is installed in at least a portion of a flexible electronic device, the secondary battery can be bent along the deformation of the electronic device.

[0440] Reference Figures 17A to 17C Description of laminated secondary battery 980. Laminated secondary battery 980 includes... Figure 17A The wound body 993 is shown. The wound body 993 includes a negative electrode 994, a positive electrode 995, and an insulator 996. (And...) Figure 16 Similarly, the winding body 950 described herein is formed by sandwiching the separator 996, causing the negative electrode 994 and the positive electrode 995 to overlap to form a laminate, and then winding the laminate.

[0441] Furthermore, the number of layers in the stack consisting of negative electrode 994, positive electrode 995, and insulator 996 can be appropriately designed according to the required capacity and component volume. Negative electrode 994 is connected to negative current collector (not shown) via one of wire electrode 997 and wire electrode 998, and positive electrode 995 is connected to positive current collector (not shown) via the other of wire electrode 997 and wire electrode 998.

[0442] like Figure 17B As shown, the wound body 993 is accommodated in the space formed by the film 981, which will become the outer packaging body, and the film 982 with a recess, which are bonded together by heat pressing or other methods. This allows for the manufacture of... Figure 17C The laminated secondary battery 980 is shown. The winding body 993 includes wire electrodes 997 and 998, and the space formed by the thin film 981 and the thin film 982 with a recess is immersed in the electrolyte.

[0443] Thin film 981 and thin film 982 with recesses are made of, for example, a metallic material such as aluminum or a resin material. When a resin material is used as the material for thin film 981 and thin film 982 with recesses, thin film 981 and thin film 982 with recesses can be deformed when force is applied from the outside, thereby manufacturing a flexible secondary battery.

[0444] In addition, Figure 17B and Figure 17C The example shown is the use of two films, but it is also possible to bend one film to form a space and accommodate the aforementioned winding 993 in that space.

[0445] By using the positive electrode active material described in the above embodiments in the positive electrode 995, a laminated secondary battery 980 with high capacity and excellent cycle characteristics can be realized.

[0446] Although Figures 17A to 17C The image shows an example of a laminated secondary battery 980 in which a wound body is included in the space formed by the film that serves as the outer packaging body, but other types of batteries may also be used. Figure 18A and Figure 18B As shown, a secondary battery includes multiple rectangular positive electrodes, separators, and negative electrodes within the space formed by the film that serves as the outer packaging.

[0447] Figure 18A The laminated battery 500 shown includes: a positive electrode 503 comprising a positive current collector 501 and a positive active material layer 502; a negative electrode 506 comprising a negative current collector 504 and a negative active material layer 505; a separator 507; an electrolyte 508; and an outer packaging 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 within the outer packaging 509. Furthermore, the outer packaging 509 is filled with the electrolyte 508. The electrolyte shown in Embodiment 2 can be used as the electrolyte 508.

[0448] exist Figure 18A In the laminated battery 500 shown, the positive current collector 501 and the negative current collector 504 also serve as terminals for electrical contact with the outside. Therefore, it is also possible to configure a portion of the positive current collector 501 and the negative current collector 504 to be exposed to the outside of the outer casing 509. Alternatively, the wire electrode can be ultrasonically welded to either the positive current collector 501 or the negative current collector 504 using a wire electrode to expose the wire electrode to the outside of the outer casing 509, without exposing the positive current collector 501 and the negative current collector 504 to the outside of the outer casing 509.

[0449] In the laminated battery 500, the outer packaging 509 can be, for example, a laminated film with the following three-layer structure: a highly flexible metal film such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as polyamide resin, polyester resin, etc. is provided on the outer surface of the metal film as the outer packaging.

[0450] also, Figure 18B An example of the cross-sectional structure of the laminated battery 500 is shown. For simplicity, Figure 18A The example shown includes two current collectors, but in reality, a battery includes multiple electrode layers.

[0451] Figure 18B One example includes 16 electrode layers. Furthermore, even with 16 electrode layers, the battery 500 is flexible. Figure 18B The diagram shows a structure with a total of 16 layers, consisting of an 8-layer negative electrode current collector 504 and an 8-layer positive electrode current collector 501. Furthermore, Figure 18B The cross-section of the negative electrode extraction section is shown, and the eight layers of negative electrode current collector 504 are ultrasonically welded. Of course, the number of electrode layers is not limited to 16; it can be more or less than 16. With a larger number of electrode layers, a secondary battery with greater capacity can be manufactured. Furthermore, with a smaller number of electrode layers, a secondary battery that is thinner and has excellent flexibility can be manufactured.

[0452] Here, Figure 19 and Figure 20 An example of the appearance of a laminated battery 500 is shown. Figure 19 and Figure 20 It includes: positive electrode 503; negative electrode 506; separator 507; outer packaging 509; positive electrode lead 510; and negative electrode lead 511.

[0453] Figure 21A The diagram shows the external appearance of the positive electrode 503 and the negative electrode 506. The positive electrode 503 includes a positive current collector 501, and a positive active material layer 502 is formed on the surface of the positive current collector 501. Furthermore, the positive electrode 503 has a portion of the positive current collector 501 exposed (hereinafter referred to as the tab region). The negative electrode 506 includes a negative current collector 504, and a negative active material layer 505 is formed on the surface of the negative current collector 504. Furthermore, the negative electrode 506 has a portion of the negative current collector 504 exposed, i.e., the tab region. The area or shape of the tab regions of the positive and negative electrodes are not limited to... Figure 21A The example shown.

[0454] [Manufacturing method of laminated secondary batteries]

[0455] Here, refer to Figure 21B and Figure 21C For Figure 19 An example of a manufacturing method for a laminated secondary battery, showing its appearance, will be illustrated.

[0456] First, the negative electrode 506, the insulator 507, and the positive electrode 503 are stacked. Figure 21B The stacked negative electrode 506, insulator 507, and positive electrode 503 are shown. Here, an example using five sets of negative electrodes and four sets of positive electrodes is shown. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode wire 510 is joined to the tab region of the outermost positive electrode. As a joining method, ultrasonic welding can be used, for example. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode wire 511 is joined to the tab region of the outermost negative electrode.

[0457] Next, a negative electrode 506, an isolator 507, and a positive electrode 503 are configured on the outer packaging 509.

[0458] Below, as Figure 21C As shown, the outer packaging body 509 is folded along the portion indicated by the dashed line. Then, the outer periphery of the outer packaging body 509 is joined. As a joining method, for example, heat pressing can be used. At this time, in order to inject the electrolyte 508 later, an area (hereinafter referred to as the inlet) that is not joined to a part (or an edge) of the outer packaging body 509 is provided.

[0459] Next, electrolyte 508 is introduced into the inside of the outer packaging 509 through an inlet provided in the outer packaging 509. Preferably, electrolyte 508 is introduced under reduced pressure or an inert gas atmosphere. Finally, the inlet is closed. In this way, a laminated battery 500 can be manufactured.

[0460] By using the positive electrode active material described in the above embodiments in the positive electrode 503, a laminated secondary battery 500 with high capacity and excellent cycle characteristics can be realized.

[0461] [Flexible rechargeable battery]

[0462] Next, refer to Figure 22A , Figure 22B1 and Figure 22B2 , Figure 22C and Figure 22D as well as Figure 23A and Figure 23B An example of a flexible secondary battery will be given.

[0463] Figure 22A A top view of the flexible battery 50 is shown. Figure 22B1 , Figure 22B2 , Figure 22C They are along Figure 22AThe diagram shows cross-sectional views of cut lines C1-C2, C3-C4, and A1-A2. The battery 50 includes an outer casing 51, and a positive electrode 11a and a negative electrode 11b housed within the outer casing 51. A wire 12a electrically connected to the positive electrode 11a and a wire 12b electrically connected to the negative electrode 11b extend outside the outer casing 51. Furthermore, an electrolyte (not shown) is sealed in the area surrounded by the outer casing 51, in addition to the positive electrode 11a and the negative electrode 11b.

[0464] Reference Figure 23A and Figure 23B This describes the positive electrode 11a and the negative electrode 11b included in battery 50. Figure 23A This is a three-dimensional diagram illustrating the stacking order of the positive electrode 11a, the negative electrode 11b, and the separator 14. Figure 23B It is a three-dimensional diagram showing wires 12a and 12b in addition to the positive electrode 11a and the negative electrode 11b.

[0465] like Figure 23A As shown, the battery 50 includes multiple rectangular positive electrodes 11a, multiple rectangular negative electrodes 11b, and multiple separators 14. The positive electrodes 11a and negative electrodes 11b each include a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on the portion of one side of the positive electrode 11a outside the tab, and a negative electrode active material layer is formed on the portion of one side of the negative electrode 11b outside the tab.

[0466] The positive electrode 11a and the negative electrode 11b are stacked in such a way that the surfaces of the positive electrode 11a that do not form a positive electrode active material layer are in contact with each other, and the surfaces of the negative electrode 11b that do not form a negative electrode active material layer are in contact with each other.

[0467] Furthermore, an insulator 14 is provided between the surface of the positive electrode 11a where the positive electrode active material layer is formed and the surface of the negative electrode 11b where the negative electrode active material layer is formed. For convenience, in Figure 23A The isolated body 14 is represented by a dashed line.

[0468] like Figure 23B As shown, multiple positive electrodes 11a are electrically connected to wire 12a in junction 15a. Furthermore, multiple negative electrodes 11b are electrically connected to wire 12b in junction 215b.

[0469] Next, refer to Figure 22B1 , Figure 22B2 , Figure 22C , Figure 22D Description of outer packaging 51.

[0470] The outer packaging 51 has a film shape and is folded in half to sandwich the positive electrode 11a and the negative electrode 11b. The outer packaging 51 includes a folded portion 61, a pair of sealing portions 62 and 63. The pair of sealing portions 62 are arranged to sandwich the positive electrode 11a and the negative electrode 11b and can also be referred to as side seals. In addition, the sealing portion 63 includes a portion that overlaps with the wires 12a and 12b and can also be referred to as top seals.

[0471] The outer packaging body 51 preferably has a wave-like shape in which ridge lines 71 and valley lines 72 are alternately arranged in the portions overlapping with the positive electrode 11a and the negative electrode 11b. In addition, the sealing portions 62 and 63 of the outer packaging body 51 are preferably flat.

[0472] Figure 22B1 It is the section cut off at the part that overlaps with edge 71. Figure 22B2 It is the section cut off at the part that overlaps with the valley bottom line 72. Figure 22B1 , Figure 22B2 These all correspond to the cross-sections in the width direction of battery 50, positive electrode 11a, and negative electrode 11b.

[0473] Here, the distance between the end of the negative electrode 11b in the width direction and the sealing portion 62 is called distance La. When the battery 50 is bent or deformed, as described later, the positive electrode 11a and the negative electrode 11b deform in a staggered manner in the length direction. At this time, if distance La is too short, the outer packaging 51 may rub strongly against the positive electrode 11a and the negative electrode 11b, causing damage to the outer packaging 51. In particular, when the metal film of the outer packaging 51 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set distance La as long as possible. On the other hand, if distance La is too long, it will lead to an increase in the volume of the battery 50.

[0474] Furthermore, it is preferable that the greater the total thickness of the stacked positive electrode 11a and negative electrode 11b, the longer the distance La between the end of the negative electrode 11b and the sealing portion 62.

[0475] More specifically, when the total thickness of the stacked positive electrode 11a, negative electrode 11b, and separator 214 is thickness t, the distance La is 0.8 times or more and 3.0 times or less of thickness t, preferably 0.9 times or more and 2.5 times or less, and more preferably 1.0 times or more and 2.0 times or less. By keeping the distance La within the above range, a compact battery with high reliability against bending can be achieved.

[0476] Furthermore, when the distance between a pair of sealing portions 62 is a distance Lb, it is preferable that the distance Lb is sufficiently larger than the width Wb of the negative electrode 11b. Therefore, when the battery 50 is repeatedly bent or deformed, even if the positive electrode 11a and the negative electrode 11b come into contact with the outer packaging 51, a portion of the positive electrode 11a and the negative electrode 11b can be offset in the width direction, thus effectively preventing friction between the positive electrode 11a and the negative electrode 11b and the outer packaging 51.

[0477] For example, the difference between the distance Lb between a pair of sealing portions 62 and the width Wb of the negative electrode 11b is more than 1.6 times and less than 6.0 times the thickness t of the positive electrode 11a and the negative electrode 11b, preferably more than 1.8 times and less than 5.0 times, and more preferably more than 2.0 times and less than 4.0 times.

[0478] In other words, the distance Lb, width Wb, and thickness t preferably satisfy the following formula 2.

[0479] [Equation 2]

[0480]

[0481] Here, a is 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, and more preferably 1.0 or more and 2.0 or less.

[0482] also, Figure 22C It is a cross-section including the conductor 12a, corresponding to the cross-section along the length of the battery 50, the positive electrode 11a, and the negative electrode 11b. For example... Figure 22C As shown, preferably, a space 73 is included in the folded portion 61 between the ends of the positive electrode 11a and the negative electrode 11b in the longitudinal direction and the outer packaging body 51.

[0483] Figure 22D A schematic diagram of the cross-section when the battery 50 is bent is shown. Figure 22D Equivalent to along Figure 22A The cross section of the cut-off line B1-B2 in the diagram.

[0484] When the battery 50 is bent, a portion of the outer packaging 51 located on the outer side of the bend deforms into an extension, while another portion of the outer packaging 51 located on the inner side of the bend deforms into a contraction. More specifically, the portion of the outer packaging 51 located on the outer side of the bend deforms with a small wave amplitude and a large wave period. On the other hand, the portion of the outer packaging 51 located on the inner side of the bend deforms with a large wave amplitude and a small wave period. By deforming the outer packaging 51 in this manner, the stress applied to the outer packaging 51 by bending can be mitigated, thus the material constituting the outer packaging 51 does not necessarily need to be elastic. As a result, the battery 50 can be bent with relatively small force without damaging the outer packaging 51.

[0485] In addition, such as Figure 22D As shown, when the battery 50 is bent, the positive electrode 11a and the negative electrode 11b are respectively offset relative to each other. At this time, since the ends of the multiple stacked positive electrodes 11a and negative electrodes 11b on the sealing part 63 side are fixed by the fixing member 17, they are offset in such a way that the offset increases as they get closer to the folded part 61. As a result, the stress applied to the positive electrode 11a and the negative electrode 11b can be mitigated, and the positive electrode 11a and the negative electrode 11b themselves do not necessarily need to be stretchable. As a result, the battery 50 can be bent without damaging the positive electrode 11a and the negative electrode 11b.

[0486] Furthermore, since a space 73 is included between the ends of the positive electrode 11a and the negative electrode 11b and the outer packaging body 51, the ends of the positive electrode 11a and the negative electrode 11b located on the inside can be offset relative to each other in a manner that does not contact the outer packaging body 51 when bending.

[0487] Figure 22A , Figure 22B1 and Figure 22B2 , Figure 22C and Figure 22D as well as Figure 23A and Figure 23B The illustrated battery 50 is a battery that is not easily damaged even with repeated bending and stretching, such as damage to the outer packaging, the positive electrode 11a, and the negative electrode 11b, and whose battery characteristics are not easily degraded. By using the positive electrode active material described in the above embodiment for the positive electrode 11a included in the battery 50, a battery with high capacity and excellent cycle characteristics can be realized.

[0488] (Implementation Method 4)

[0489] In this embodiment, an example of installing a secondary battery according to one embodiment of the present invention in an electronic device is described.

[0490] first, Figures 24A to 24G An example is shown of mounting the flexible secondary battery described in part of Embodiment 3 onto an electronic device. Examples of electronic devices that use flexible secondary batteries include television sets (also called televisions or television receivers), displays for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, portable information terminals, sound reproduction devices, pinball machines, and other large game machines.

[0491] In addition, flexible secondary batteries can be assembled along the curved surfaces of the interior or exterior walls of houses and high-rise buildings, or the interior or exterior of automobiles.

[0492] Figure 24AAn example of a mobile phone is shown. In addition to a display unit 7402 assembled in a housing 7401, the mobile phone 7400 includes operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, etc. Furthermore, the mobile phone 7400 has a secondary battery 7407. By using a secondary battery according to one embodiment of the present invention as the aforementioned secondary battery 7407, a lightweight mobile phone with a long service life can be provided.

[0493] Figure 24B The image shows the mobile phone 7400 bent. When the mobile phone 7400 is deformed and bent as a whole by external force, the secondary battery 7407 installed inside it is also bent. Figure 24C The diagram shows the state of the bent secondary battery 7407. The secondary battery 7407 is a thin-film rechargeable battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has conductive electrodes 7408 electrically connected to the current collector 7409. For example, the current collector 2409 is a copper foil, a portion of which is alloyed with gallium to improve adhesion to the active material layer in contact with the current collector, thereby improving the reliability of the secondary battery 7407 in a bent state.

[0494] Figure 24D An example of a bracelet-type display device is shown. The portable display device 7100 includes a frame 7101, a display section 7102, operation buttons 7103, and a secondary battery 7104. Furthermore, Figure 24E A bent secondary battery 7104 is shown. When the bent secondary battery 7104 is worn on a user's arm, the frame of the secondary battery 7104 deforms, causing a change in the curvature of part or all of the secondary battery 7104. The radius of curvature is the value of the degree of bending at any point on the curve, expressed as the radius of an equivalent circle, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the frame or the main surface of the secondary battery 7104 deforms within a range of a radius of curvature of 40 mm or more and 150 mm or less. High reliability can be maintained as long as the radius of curvature in the main surface of the secondary battery 7104 is within the range of 40 mm or more and 150 mm or less. By using a secondary battery according to one embodiment of the present invention as the aforementioned secondary battery 7104, a lightweight and long-lasting portable display device can be provided.

[0495] Figure 24F This is an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a frame 7201, a display unit 7202, a strap 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, etc.

[0496] The portable information terminal 7200 can run various applications such as mobile phone, email, article reading and writing, music playback, network communication, and computer games.

[0497] The display surface of the display unit 7202 is curved, allowing for display along the curved surface. Furthermore, the display unit 7202 is equipped with a touch sensor, allowing operation via touch of the screen using a finger or stylus. For example, an application can be launched by touching the icon 7207 displayed on the display unit 7202.

[0498] In addition to setting the time, the operation button 7205 can also have various functions such as power switch, wireless communication switch, setting and canceling silent mode, and setting and canceling power saving mode. For example, the functions of the operation button 7205 can be freely configured by utilizing the operating system integrated in the portable information terminal 7200.

[0499] Furthermore, the portable information terminal 7200 can perform short-range wireless communication according to communication standards. For example, hands-free calling can be made by communicating with a wirelessly wireless headset.

[0500] Furthermore, the portable information terminal 7200 has an input / output terminal 7206, which allows it to directly send data to or receive data from other information terminals via a connector. It can also be charged via the input / output terminal 7206. Alternatively, charging can be performed wirelessly without using the input / output terminal 7206.

[0501] The display unit 7202 of the portable information terminal 7200 includes a secondary battery according to one embodiment of the present invention. By using the secondary battery according to one embodiment of the present invention, a lightweight and long-lasting portable information terminal can be provided. For example, a bent-state... Figure 24E The secondary battery 7104 shown is assembled inside the frame 7201, or the secondary battery 7104 is assembled inside the strap 7203 in a bendable state.

[0502] The portable information terminal 7200 preferably includes sensors. Examples of preferred sensors include fingerprint sensors, pulse sensors, body temperature sensors, touch sensors, pressure sensors, and accelerometers.

[0503] Figure 24G An example of a sleeve-type display device is shown. The display device 7300 includes a display unit 7304 and a secondary battery according to one embodiment of the present invention. The display device 7300 may also include a touch sensor in the display unit 7304 and be used as a portable information terminal.

[0504] The display surface of the display unit 7304 is curved, allowing for display along the curved surface. Furthermore, the display device 7300 can change the display configuration using short-range wireless communication, which is standardized for communication.

[0505] The display device 7300 has input / output terminals, allowing it to directly send data to or receive data from other information terminals via connectors. Furthermore, it can be charged via the input / output terminals. Additionally, charging can also be performed wirelessly without using the input / output terminals.

[0506] By using a secondary battery from one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long service life can be provided.

[0507] In addition, refer to Figure 24H , Figures 25A to 25C and Figure 26 This section describes an example of installing a secondary battery with excellent cycle characteristics, as shown in the above embodiments, into an electronic device.

[0508] By using the secondary battery of one embodiment of the present invention as a secondary battery for everyday electronic devices, lightweight products with long service life can be provided. Examples of everyday electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. The secondary batteries in these products are expected to be rod-shaped, small, lightweight, and high-capacity for easy handling by the user.

[0509] Figure 24H This is a three-dimensional diagram of a device known as an e-liquid-containing smoking device (electronic cigarette). Figure 24H In this device, the electronic cigarette 7500 includes: an atomizer 7501 including a heating element; a secondary battery 7504 supplying power to the atomizer; and a cartridge 7502 including a liquid supply container and sensors. To improve safety, a protection circuit to prevent overcharging and over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. Figure 24H The secondary battery 7504 shown includes external terminals for connection to a charger. When removed, the secondary battery 7504 is located at the top, thus its overall length and weight are preferably short. Since the secondary battery of one embodiment of the present invention has high capacity and excellent cycle characteristics, a small and lightweight electronic cigarette 7500 that can be used for extended periods can be provided.

[0510] then, Figure 25A and Figure 25B An example of a tablet terminal that can be folded in half is shown. Figure 25A and Figure 25BThe tablet terminal 9600 shown includes a frame 9630a, a frame 9630b, a movable part 9640 connecting the frames 9630a and 9630b, a display unit 9631 having display units 9631a and 9631b, a display mode switching switch 9626, a switch 9627, a power saving mode switching switch 9625, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display unit 9631, a tablet terminal with a larger display unit can be realized. Figure 25A This indicates that the tablet terminal 9600 is open. Figure 25B This shows the state of the tablet terminal 9600 when closed.

[0511] The tablet terminal 9600 has a battery 9635 inside the frame 9630a and frame 9630b. The battery 9635 is disposed in the frame 9630a and frame 9630b through the movable part 9640.

[0512] In display unit 9631a, a portion of it can be used as a touchscreen area, and data can be input by touching the displayed operation keys. Furthermore, as an example, one half of display unit 9631a may only have display functionality, while the other half has touchscreen functionality, but this structure is not limited to. A structure where the entire area of ​​display unit 9631a has touchscreen functionality can be adopted. For example, the entire surface of display unit 9631a can be used as a touchscreen by displaying keyboard buttons, and display unit 9631b can be used to display a screen.

[0513] Furthermore, in the display unit 9631b, a portion of the display unit 9631b may also be used as a touchscreen area 9632b, similar to the display unit 9631a. Additionally, keyboard buttons can be displayed on the display unit 9631b by touching the location of the keyboard display switching button 9639 on the touchscreen using a finger or stylus.

[0514] In addition, touch input can be performed simultaneously on both the touchscreen area 9632a and the touchscreen area 9632b.

[0515] Additionally, the display mode switch 9626 allows switching between portrait and landscape display orientations, as well as selecting between monochrome and color display. Based on the amount of ambient light detected by the light sensor built into the tablet terminal 9600, the power-saving mode switch 9625 sets the display brightness to the most suitable level. Besides the light sensor, the tablet terminal may also incorporate other detection devices such as a gyroscope and an accelerometer to detect tilt.

[0516] also, Figure 25AThe example shown is an example where the display area of ​​display unit 9631a is the same as that of display unit 9631b, but it is not limited to this. The size of one of them can be different from that of the other, and their display quality can also be different. For example, a structure can be adopted in which one of display unit 9631a and display unit 9631b can perform a high-resolution display compared to the other.

[0517] Figure 25B The tablet terminal is in a folded state, and the tablet terminal includes a frame 9630, a solar cell 9633, and a charge / discharge control circuit 9634 with a DC-DC converter 9636. A secondary battery according to one embodiment of the present invention is used as the energy storage device 9635.

[0518] Furthermore, as described above, the tablet terminal 9600 is foldable, so when not in use, the frames 9630a and 9630b can be folded over each other. By folding the frames 9630a and 9630b, the display units 9631a and 9631b can be protected, thereby improving the durability of the tablet terminal 9600. Moreover, since the energy storage element 9635 using the secondary battery according to one embodiment of the present invention has high capacity and excellent cycle characteristics, a tablet terminal 9600 that can be used for extended periods can be provided.

[0519] also, Figure 25A and Figure 25B The tablet terminal shown may also have the following functions: displaying various types of information (static images, dynamic images, text images, etc.); displaying calendars, dates, or times on the display; touch input for touch input or editing of information displayed on the display; and control processing through various software (programs), etc.

[0520] By utilizing solar cells 9633 mounted on the surface of the tablet terminal, power can be supplied to the touchscreen, display unit, or image signal processing unit. Note that the solar cells 9633 can be disposed on one or both surfaces of the frame 9630, allowing for efficient charging of the energy storage unit 9635. Using a lithium-ion battery as the energy storage unit 9635 offers advantages such as miniaturization.

[0521] In addition, refer to Figure 25C The block diagram shown is for Figure 25B The structure and operation of the charge / discharge control circuit 9634 shown are explained. Figure 25C The diagram shows a solar cell 9633, an energy storage unit 9635, a DC-DC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The energy storage unit 9635, DC-DC converter 9636, converter 9637, and switches SW1 to SW3 correspond to... Figure 25B The charging and discharging control circuit 9634 is shown.

[0522] First, an example of operation when the solar cell 9633 generates electricity using external light will be explained. A DC-DC converter 9636 is used to boost or buck the power generated by the solar cell to make it a voltage used to charge the energy storage unit 9635. Furthermore, when the display unit 9631 is operated using power from the solar cell 9633, switch SW1 is turned on, and converter 9637 boosts or bucks the voltage to the voltage required by the display unit 9631. Alternatively, a structure can be adopted where switch SW1 is turned off and switch SW2 is turned on when the display unit 9631 is not displaying anything, thereby charging the energy storage unit 9635.

[0523] Note that the solar cell 9633 is shown as an example of a power generation unit, but it is not limited to this. Other power generation units, such as piezoelectric elements or thermoelectric conversion elements (Peltier elements), can also be used to charge the energy storage unit 9635. For example, a contactless power transmission module capable of wireless (contactless) power transmission and reception can also be used for charging, or a combination of other charging methods can be used.

[0524] Figure 26 Examples of other electronic devices are shown. Figure 26 In this context, the display device 8000 is an example of an electronic device using a secondary battery 8004 according to an embodiment of the present invention. Specifically, the display device 8000 corresponds to a television broadcast receiving display device, including a housing 8001, a display unit 8002, a speaker unit 8003, and a secondary battery 8004, etc. The secondary battery 8004 according to an embodiment of the present invention is disposed inside the housing 8001. The display device 8000 can receive power from commercial power sources and also utilize the power stored in the secondary battery 8004. Therefore, even when power from commercial power sources cannot be received due to power outages or other reasons, the display device 8000 can be used as an uninterruptible power source by using the secondary battery 8004 according to an embodiment of the present invention.

[0525] As the display unit 8002, semiconductor display devices such as liquid crystal display devices, light-emitting devices having light-emitting elements such as organic EL elements in each pixel, electrophoretic display devices, digital micromirror devices (DMD), plasma display panels (PDP), and field emission displays (FED) can be used.

[0526] In addition to display devices for receiving television broadcasts, display devices also include all display devices for displaying information, such as display devices for personal computers or display devices for advertising.

[0527] exist Figure 26 In this context, the recessed lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to an embodiment of the present invention. Specifically, the lighting device 8100 includes a frame 8101, a light source 8102, and a secondary battery 8103, etc. Although in Figure 26 The illustration shows a secondary battery 8103 installed inside a ceiling 8104 housing a frame 8101 and a light source 8102; however, the secondary battery 8103 can also be installed inside the frame 8101. The lighting device 8100 can receive power from a commercial power source or use the power stored in the secondary battery 8103. Therefore, even when power from a commercial power source is unavailable due to a power outage, the lighting device 8100 can still be used by employing the secondary battery 8103 according to one embodiment of the invention as an uninterruptible power source.

[0528] In addition, although Figure 26 The example shown is an inlaid lighting device 8100 installed on the ceiling 8104, but the secondary battery according to one embodiment of the present invention can be used for inlaid lighting devices installed outside the ceiling 8104, such as side walls 8105, floor 8106 or window 8107, and can also be used for tabletop lighting devices, etc.

[0529] Furthermore, as the light source 8102, an artificial light source that artificially generates light using electricity can be used. Specifically, examples of the aforementioned artificial light sources include discharge lamps such as incandescent bulbs and fluorescent lamps, as well as light-emitting elements such as LEDs or organic EL elements.

[0530] exist Figure 26 In this context, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to an embodiment of the present invention. Specifically, the indoor unit 8200 includes a frame 8201, an air outlet 8202, and a secondary battery 8203, etc. Although in Figure 26 The illustration shows a secondary battery 8203 installed in the indoor unit 8200, but the secondary battery 8203 can also be installed in the outdoor unit 8204. Alternatively, the secondary battery 8203 can be installed in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or use the power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is installed in both the indoor unit 8200 and the outdoor unit 8204, even when power from a commercial power source cannot be received due to a power outage or other reasons, the air conditioner can still be used by using the secondary battery 8203 according to an embodiment of the present invention as an uninterruptible power supply.

[0531] In addition, although Figure 26The example shown is a split-type air conditioner consisting of an indoor unit and an outdoor unit, but a secondary battery according to an embodiment of the present invention can also be used in an integrated air conditioner that has the functions of an indoor unit and an outdoor unit in one frame.

[0532] exist Figure 26 In this context, the electric refrigerator / freezer 8300 is an example of an electronic device using a secondary battery 8304 according to an embodiment of the present invention. Specifically, the electric refrigerator / freezer 8300 includes a frame 8301, a refrigerator door 8302, a freezer door 8303, and a secondary battery 8304, etc. Figure 26 In this configuration, a secondary battery 8304 is disposed inside the frame 8301. The electric refrigerator / freezer 8300 can receive power from a commercial power source or utilize the power stored in the secondary battery 8304. Therefore, even when power from a commercial power source cannot be received due to a power outage or other reasons, the electric refrigerator / freezer 8300 can be utilized by using the secondary battery 8304 according to an embodiment of the present invention as an uninterruptible power source.

[0533] Among the aforementioned electronic devices, high-frequency heating devices such as microwave ovens and rice cookers require high power for short periods of time. Therefore, by using an energy storage device according to an embodiment of the present invention as an auxiliary power source to supplement power when commercial power supply cannot provide sufficient power, the main switch of the commercial power supply can be prevented from tripping when the electronic devices are in use.

[0534] Furthermore, during periods when electronic devices are not used, especially when the ratio of actual electricity used to the total electricity available from commercial power sources (referred to as electricity usage rate) is low, electricity is stored in secondary batteries, thereby suppressing increased electricity usage during periods outside of these periods. For example, in the case of an electric refrigerator / freezer 8300, electricity is stored in secondary batteries 8304 at night when the temperature is low and the refrigerator door 8302 or freezer door 8303 is not opened or closed. During the day when the temperature is high and the refrigerator door 8302 or freezer door 8303 is opened or closed, secondary batteries 8304 are used as auxiliary power, thereby suppressing daytime electricity usage.

[0535] By employing one embodiment of the present invention, the cycle characteristics and reliability of the secondary battery can be improved. Furthermore, by employing one embodiment of the present invention, a high-capacity secondary battery can be achieved, thereby improving the characteristics of the secondary battery and enabling the secondary battery itself to be miniaturized and lightweight. Therefore, by installing the secondary battery of one embodiment of the present invention in the electronic device described in this embodiment, a longer service life and a lighter electronic device can be provided. This embodiment can be implemented in suitable combinations with other embodiments.

[0536] (Implementation Method 5)

[0537] In this embodiment, an example is shown of installing a secondary battery according to one embodiment of the present invention in a vehicle.

[0538] When a secondary battery is installed in a vehicle, it can enable a new generation of clean energy vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV), or plug-in hybrid electric vehicles (PHEV).

[0539] exist Figures 27A to 27C The example shown is a vehicle using a secondary battery according to one embodiment of the present invention. Figure 27A The illustrated vehicle 8400 is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, vehicle 8400 is a hybrid vehicle that can appropriately use an electric motor or an engine as a power source for driving. By using a secondary battery according to one embodiment of the present invention, a vehicle with a long driving range can be realized. Furthermore, vehicle 8400 is equipped with a secondary battery. As a secondary battery, it can be used to... Figure 12C and Figure 12D The small secondary battery modules shown are arranged on the floor of the vehicle for use. Furthermore, multiple modules can be combined. Figures 17A to 17C The battery pack, consisting of a secondary battery, is installed on the floor inside the vehicle. The secondary battery not only powers the electric motor 8406, but also supplies power to lighting devices such as the headlights 8401 or interior lights (not shown).

[0540] Furthermore, the secondary battery can supply power to display devices such as the speedometer and tachometer in the car 8400. Additionally, the secondary battery can supply power to semiconductor devices such as the navigation system in the car 8400.

[0541] exist Figure 27B The car 8500 shown can receive power from an external charging device using a plug-in or contactless power supply method to charge its secondary battery. Figure 27B This illustration shows the charging of secondary batteries 8024 and 8025 installed in a vehicle 8500 from a ground-mounted charging device 8021 via a cable 8022. During charging, the charging method and connector specifications can be appropriately determined according to the specifications of CHAdeMO (registered trademark) or the "Combined Charging System." The charging device 8021 can also utilize power from charging stations in commercial facilities or from homes. For example, the secondary battery 8024 installed in the vehicle 8500 can be charged by supplying power from an external source using plug-in technology. AC power can be converted to DC power using a conversion device such as an AC / DC converter for charging.

[0542] Furthermore, although not illustrated, the receiving device can be installed in the vehicle and charged by receiving power from a ground-based power supply device without contact. When using a contactless power supply method, charging can be performed both while the vehicle is parked and while it is in motion, by assembling the power supply device in the road or exterior wall. Additionally, this contactless power supply method can be used for power transmission and reception between vehicles. Moreover, solar panels can be installed on the exterior of the vehicle to charge the secondary battery while it is parked or in motion. Such contactless power supply can be achieved using electromagnetic induction or magnetic field resonance.

[0543] Figure 27C This is an example of a two-wheeled vehicle using a secondary battery according to one embodiment of the present invention. Figure 27C The small motorcycle 8600 shown includes a secondary battery 8602, a rearview mirror 8601, and turn signals 8603. The secondary battery 8602 can power the turn signals 8603.

[0544] In addition, Figure 27C In the illustrated mini motorcycle 8600, the secondary battery 8602 can be stored in the under-seat storage box 8604. Even though the under-seat storage box 8604 is small, the secondary battery 8602 can still be stored in it. The secondary battery 8602 is removable, so it can be moved indoors to charge when needed, and stored away before riding.

[0545] By employing one embodiment of the present invention, the cycle characteristics and capacity of the secondary battery can be improved. This allows for a smaller and lighter secondary battery. Furthermore, the ability to make the secondary battery smaller and lighter contributes to vehicle weight reduction, thereby extending driving range. Additionally, the secondary battery installed in the vehicle can be used as a power source outside the vehicle. This, for example, avoids the use of commercial power during peak electricity demand periods. Avoiding the use of commercial power during peak electricity demand periods helps save energy and reduce carbon dioxide emissions. Moreover, excellent cycle characteristics allow for longer-term use of the secondary battery, thereby reducing the use of rare metals such as cobalt.

[0546] This implementation method can be appropriately combined with other implementation methods.

[0547] [Example 1]

[0548] In this embodiment, a positive electrode active material according to one embodiment of the present invention is formed, and the results of STEM observation of the positive electrode active material, the results of fast Fourier transform of the TEM image, and the results of energy dispersive X-ray analysis (EDX) are described. Furthermore, the results of evaluating the characteristics of a secondary battery containing this positive electrode active material are explained.

[0549] [Formation of positive electrode active material]

[0550] Sample 01

[0551] In this embodiment, a positive electrode active material is formed as sample 01, which includes lithium cobalt oxide as a composite oxide of lithium and a first transition metal contained in the first region, lithium titanate as a second transition metal contained in the second region, and magnesium oxide as an oxide of a main group element contained in the third region.

[0552] In this embodiment, lithium cobalt oxide particles (manufactured by Nippon Chemical Industries, Ltd., trade name: C-20F) are used as the starting material. Therefore, steps 12 and 13 described in Embodiment 1 are omitted in this embodiment. The aforementioned lithium cobalt oxide particles are lithium cobalt oxide particles with a particle size of about 20 μm and containing fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus in the region that can be analyzed by XPS.

[0553] Next, as step 14, lithium cobalt oxide particles containing magnesium and fluorine are coated using a titanium-containing material via a sol-gel method. Specifically, TTIP is dissolved in isopropanol to prepare an isopropanol solution of TTIP. Then, lithium cobalt oxide particles are mixed into this solution such that the ratio of TTIP to lithium cobalt oxide containing magnesium and fluorine is 0.01 ml / g.

[0554] The above mixture was stirred for 4 hours at 25°C and 90% RH using a magnetic stirrer. This treatment caused water in the atmosphere to undergo hydrolysis and condensation reactions with TTIP, thereby forming a titanium-containing layer on the surface of the lithium cobalt oxide particles containing magnesium and fluorine.

[0555] The treated mixture was filtered, and the residue was collected. Kiriyama filter paper (No. 4) was used as the filter.

[0556] The collected residue was dried in a vacuum at 70°C for 1 hour.

[0557] Next, the lithium cobalt oxide particles covered with the titanium-containing material are heated. This heating is carried out using a furnace under the following conditions: dry air flow rate of 10 L / min; temperature of 800°C (heating rate of 200°C / hour); holding time of 2 hours. The dew point of the dry air is preferably below -109°C.

[0558] Next, the heated particles are cooled to room temperature. The cooling time from the holding temperature to room temperature is between 10 and 15 hours. Then, a grinding process is performed. The grinding process is carried out by sieving using a sieve with a pore size of 53 μm.

[0559] Finally, the cooled particles were collected to obtain the positive electrode active material of sample 01.

[0560] Sample 02

[0561] As a comparative example, sample 02 was formed by heating lithium cobalt oxide particles containing magnesium and fluorine that were not covered by a material containing titanium.

[0562] The lithium cobalt oxide particles containing magnesium and fluorine are lithium cobalt oxide particles manufactured by Nippon Kagaku Kogyo Co., Ltd. (trade name: C-20F).

[0563] Lithium cobalt oxide particles containing magnesium and fluorine were heated. The heating was carried out under the following conditions: temperature 800℃ (heating rate 200℃ / hour); holding time 2 hours; oxygen flow rate 10 L / min.

[0564] The heated particles were cooled and screened in the same manner as sample 01 to obtain the positive electrode active material of sample 02.

[0565] Sample 02 can be considered as a positive electrode active material containing lithium cobalt oxide inside and having a magnesium-containing region on its surface.

[0566] Sample 03

[0567] As a comparative example, sample 03 was formed by heating lithium cobalt oxide particles after forming a titanium-containing region in them using a sol-gel method.

[0568] The lithium cobalt oxide particles used were manufactured by Nippon Kagaku Kogyo Co., Ltd. (trade name: C-10N). In these lithium cobalt oxide particles, approximately 1 at% fluorine was detected, but no magnesium was detected by XPS.

[0569] Similar to Sample 01, a titanium-containing region was formed in the lithium cobalt oxide particles using the sol-gel method, and the lithium cobalt oxide particles were then dried, heated, cooled, and sieved. The resulting lithium cobalt oxide particles were used as the positive electrode active material for Sample 03.

[0570] Sample 03 can be considered as a positive electrode active material containing lithium cobalt oxide inside and having a titanium-containing region on its surface.

[0571] Sample 04

[0572] As a comparative example, sample 04 uses unheated lithium cobalt oxide particles.

[0573] The lithium cobalt oxide particles used are those manufactured by Nippon Kagaku Kogyo Co., Ltd. (trade name: C-10N).

[0574] Sample 04 is a positive electrode active material without a coating layer.

[0575] Sample 05

[0576] As a comparative example, sample 05 uses unheated lithium cobalt oxide particles containing magnesium and fluorine.

[0577] The lithium cobalt oxide particles containing magnesium and fluorine were manufactured by Nippon Kagaku Kogyo Co., Ltd. (trade name: C-20F). In other words, the starting material for Sample 05 was the same as that for Sample 01.

[0578] Table 1 shows the conditions for samples 01 to 05.

[0579] [Table 1]

[0580] condition Sample 01 <![CDATA[LiCoO2 + Mg + F, covered with titanium-containing material, with heating]]> Sample 02 <![CDATA[LiCoO2 + Mg + F, with heating]]> Sample 03 <![CDATA[LiCoO 2、 Covered by a material containing titanium, and heated. Sample 04 <![CDATA[LiCoO2, no heating]]> Sample 05 <![CDATA[LiCoO2 + Mg + F, without heating]]>

[0581] [STEM]

[0582] The positive electrode active material of the obtained sample 01 was observed using an electron microscope (JEM-ARM200F manufactured by Nippon Electron Co., Ltd.) at an accelerating voltage of 200kV. Figure 28 The obtained electron microscope image is shown. For example... Figure 28 As shown, the positive electrode active material is considered to comprise three distinct regions: a first region 101, a second region 102, and a third region 103. The third region 103 is considered 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, while the crystal orientations of the second region 102 and the third region 103 are partially aligned.

[0583] [STEM-FET]

[0584] Figure 29A1 Show Figure 28 The image shows a region 103 in the STEM image, obtained by Fast Fourier Transform (FFT). Figure 29A2 In the middle, it is represented by a cross. Figure 29A1 Draw the center point O and circle the bright spots A, B, and C. Similarly, Figure 29B1 The FFT image of region 102FFT is shown. Figure 29B2 In the middle, it is represented by a cross. Figure 29B1 Draw the center point O and circle the bright spots A, B, and C. In addition, Figure 29C1The FFT image of region 101 is shown. Figure 29C2 In the middle, it is represented by a cross. Figure 29C1 Draw the center point O and circle the highlights A, B and C.

[0585] exist Figure 29A2 In the diagram, the distance *d* between bright spot A and center point O is 0.256 nm, the distance *d* between bright spot B and center point O is 0.241 nm, and the distance *d* between bright spot C and center point O is 0.209 nm. Furthermore, ∠COA is 121°, ∠COB is 52°, and ∠AOB is 69°. Therefore, region 103FFT contains magnesium oxide (MgO, cubic crystal).

[0586] Similarly, in Figure 29B2 In the diagram, the distance *d* between bright spot A and center point O is 0.238 nm, the distance *d* between bright spot B and center point O is 0.225 nm, and the distance *d* between bright spot C and center point O is 0.198 nm. Furthermore, ∠COA is 123°, ∠COB is 52°, and ∠AOB is 71°. Therefore, region 102FFT contains lithium titanate (LiTiO2, cubic crystal).

[0587] exist Figure 29C2 In the diagram, the distance *d* between bright spot A and center point O is 0.240 nm, the distance *d* between bright spot B and center point O is 0.235 nm, and the distance *d* between bright spot C and center point O is 0.196 nm. Furthermore, ∠COA is 126°, ∠COB is 52°, and ∠AOB is 74°. Therefore, region 101FFT contains lithium cobalt oxide (LiCoO2, triangular crystal).

[0588] [EDX]

[0589] Figure 30A1 , Figure 30A2 , Figure 30B1 , Figure 30B2 , Figure 30C1 as well as Figure 30C2 The image shows a high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the positive electrode active material of sample 01 and an elemental distribution map using EDX. Figure 30A1 Showing HAADF-STEM images, Figure 30A2 The elemental distribution diagram of oxygen atoms is shown. Figure 30B1 The elemental distribution diagram of cobalt atoms is shown. Figure 30B2 The elemental distribution diagram of fluorine atoms is shown. Figure 30C1 The elemental distribution of titanium atoms is shown, and Figure 30C2 This shows the elemental distribution of magnesium atoms. Figure 30A2 , Figure 30B1 , Figure 30B2 , Figure 30C1 , Figure 30C2 , Figure 31A2 , Figure 31B1 , Figure 31B2 , Figure 31C1 as well as Figure 31C2 In the EDX element distribution map, white represents the number of elements below the detection limit, and the more elements there are, the closer the white area is to black.

[0590] Depend on Figure 30A2 and Figure 30B1 It can be seen that oxygen atoms and cobalt atoms are distributed throughout the entire positive electrode active material particle. Conversely, from... Figure 30B2 , Figure 30C1 , Figure 30C2 It can be seen that fluorine atoms, titanium atoms, and magnesium atoms are segregated in the region closer to the surface of the positive electrode active material.

[0591] Figure 31A1 , Figure 31A2 , Figure 31B1 , Figure 31B2 , Figure 31C1 as well as Figure 31C2 The HAADF-STEM image and elemental distribution map using EDX of the positive electrode active material of the comparative example of sample 05 are shown. Figure 31A1 Showing HAADF-STEM images, Figure 31A2 The elemental distribution diagram of oxygen atoms is shown. Figure 31B1 The elemental distribution diagram of cobalt atoms is shown. Figure 31B2 The elemental distribution diagram of fluorine atoms is shown. Figure 31C1 The elemental distribution of titanium atoms is shown, and Figure 31C2 The elemental distribution of magnesium atoms is shown.

[0592] Depend on Figure 31B2 and Figure 31C2 It can be seen that even in sample 05, which was not heated, magnesium and fluorine segregated to some extent near the surface.

[0593] [EDX Linear Analysis]

[0594] Figure 32 The results of TEM-EDX line analysis of the cross section near the surface of the positive electrode active material of sample 01 are shown. Figure 32 This is a graph showing the data detected on the line connecting the outside and inside of the positive electrode active material of sample 01, with 0 nm representing the outside of the positive electrode active material and 14 nm representing the inside of the particle. The analytical region of EDX is easily expanded, thus sometimes detecting elements not only in the center of the electron beam irradiation area but also in its surroundings.

[0595] Depend on Figure 32It can be seen that magnesium and titanium peaks exist near the surface of the positive electrode active material in sample 01, with magnesium distribution closer to the surface compared to titanium distribution. It can also be seen that the magnesium peak is closer to the surface than the titanium peak; cobalt and oxygen are present from the outermost surface of the positive electrode active material particles.

[0596] like Figure 32 As shown, fluorine is almost undetectable, which is believed to be because it is difficult to detect fluorine as a light element using EDX.

[0597] As can be seen from the above STEM images, FFT images, elemental distribution maps using EDX, and EDX line analysis, sample 01 is a positive electrode active material of one embodiment of the present invention. This positive electrode active material includes a first region containing lithium cobalt oxide, a second region containing lithium, titanium, cobalt, and oxygen, and a third region containing magnesium and oxygen. Therefore, in sample 01, a portion of the second region overlaps with a portion of the third region.

[0598] exist Figure 32 In this study, the oxygen detection level stabilized at a distance of 4 nm or more. Therefore, in this embodiment, the average oxygen detection level O in the stable region was calculated. ave To make the measured value as close as possible to the average value O ave 50%, or 0.5O ave The distance x between the measurement points is assumed to be the surface of the positive electrode active material particle.

[0599] In this embodiment, the average oxygen detection amount O in the range of 4 nm to 14 nm is... ave The value is 674.2. The measurement point closest to 50% of 674.2, i.e., 337.1, represents a distance of 1.71 nm on the x-axis. Therefore, in this embodiment, Figure 32 The distance of 1.71 nm is assumed to be the surface of the positive electrode active material particles.

[0600] When in Figure 32 When the surface of the positive electrode active material particle is 1.71 nm away, the peak values ​​of magnesium and titanium are located at 0.72 nm and 1.00 nm away from the surface of the positive electrode active material particle, respectively.

[0601] The magnesium concentration is above 1 / 5 of the peak value up to a distance of 4.42 nm, which is 2.71 nm from the surface of the positive electrode active material particles. At a distance above 4.57 nm, which is more than 2.86 nm from the surface of the positive electrode active material particles, the measured magnesium value is less than 1 / 5 of the peak value. Therefore, a third region is formed in sample 01, extending to a depth of 2.71 nm from the surface.

[0602] Furthermore, the concentration of titanium is more than half of the peak value from a distance of 2.14 nm to a distance of 3.42 nm. That is to say, a second region is formed from the surface of the positive electrode active material particles to a depth of more than 0.43 nm and less than 1.71 nm.

[0603] The following describes the evaluation results of the charge-discharge characteristics of secondary batteries made using the positive electrode active materials of samples 01 to 05 formed as described above.

[0604] [Manufacturing of secondary batteries]

[0605] A coin-shaped secondary battery (diameter: 20 mm, height: 3.2 mm) of CR2032 was made using the positive electrode active materials of samples 01 to 05 formed as described above.

[0606] As the positive electrode, a positive electrode manufactured in the following manner is used: a slurry made by mixing the positive electrode active material (LCO) manufactured above, acetylene black (AB), and polyvinylidene fluoride (PVDF) in a weight ratio of 95:2.5:2.5 is applied to the current collector.

[0607] Lithium metal is used as the counter electrode.

[0608] The electrolyte used is 1 mol / L lithium hexafluorophosphate (LiPF6). The electrolyte is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, along with 2 wt% vinylene carbonate (VC).

[0609] The positive and negative electrode containers are made of stainless steel (SUS).

[0610] [Evaluation of charge / discharge characteristics]

[0611] Next, the charge-discharge characteristics of the secondary batteries formed as described above (samples 01 to 05) were evaluated. The measurement temperature was 25°C. Twenty cycles of charge and discharge were performed under the following conditions: 4.6V (CCCV, 0.5C, 0.01C cutoff current) and 2.5V (CC, 0.5C). Here, 1C was set to 137 mA / g, which is the current value per unit weight of the positive electrode active material.

[0612] Figure 33 This is a graph showing the charge-discharge characteristics of a secondary battery using the positive electrode active material of sample 01. Figure 33 The results show superior charge-discharge characteristics with a sufficiently wide flat region. The results of 20 charge-discharge cycles largely overlap, demonstrating superior charge-discharge characteristics.

[0613] Figure 34This is a graph showing the charge-discharge characteristics of the secondary battery of sample 05, which is a comparative example. Although it exhibits excellent charge-discharge characteristics in the initial cycling phase, as... Figure 34 As the arrows in the diagram show, the charge / discharge capacity decreases with increasing number of cycles.

[0614] [Evaluation of Cyclic Characteristics]

[0615] Charging at 4.4V

[0616] The cycle characteristics of the secondary batteries of samples 01 and 05 charged at 4.4V were evaluated. The measurement temperature was 25°C. Charging and discharging were performed at 4.4V (CCCV, 0.5C, 0.01C cutoff current) and 2.5V (CC, 0.5C), respectively.

[0617] Figure 35 The cycle characteristics of a secondary battery charged at 4.4V are shown. Figure 35 In the diagram, the solid and dashed lines represent secondary batteries containing the positive electrode active materials of samples 01 and 05, respectively. For example... Figure 35 As shown, the secondary battery containing sample 01 maintained 99.5% of its energy density even after 50 charge-discharge cycles, exhibiting extremely superior cycle characteristics. In the secondary battery containing sample 05, the energy density retention rate was 94.3% after 50 cycles.

[0618] Charging at 4.6V

[0619] The cycle characteristics of the secondary batteries from samples 01 to 04, charged at 4.6V, were evaluated. The measurement temperature was 25°C. Charging and discharging were performed at 4.6V (CCCV, 0.5C, 0.01C cutoff current) and 2.5V (CC, 0.5C), respectively.

[0620] Figure 36 The cycling characteristics are shown when charged at 4.6V. (Example) Figure 36 As shown, in the secondary battery containing sample 01, which is an embodiment of the present invention, an energy density retention rate of 94.1% was obtained even after 50 charge-discharge cycles at a high voltage of 4.6V, exhibiting extremely superior cycle characteristics. On the other hand, the secondary batteries containing the positive electrode active materials of samples 02 to 04, which are comparative examples, are inferior to sample 01. For example, in sample 04, the energy density retention rate after 50 charge-discharge cycles is 33.2%.

[0621] Therefore, it can be seen that the positive electrode active material having the structure of one embodiment of the present invention exhibits significant effects when charged and discharged at a voltage higher than 4.4V.

[0622] [Example 2]

[0623] In this embodiment, a positive electrode active material according to one embodiment of the present invention is formed, and the results of analyses performed differently from those in Example 1 are explained. Furthermore, the results of evaluating the characteristics of a secondary battery containing this positive electrode active material under conditions different from those in Example 1 are explained.

[0624] In this embodiment, a positive electrode active material is formed, which includes lithium cobalt oxide as a composite oxide of lithium and a first transition metal contained in a first region, lithium titanate as a second transition metal contained in a second region, and magnesium oxide as an oxide of a main group element contained in a third region.

[0625] [Formation of positive electrode active material, manufacturing of secondary batteries]

[0626] Sample 06 and Sample 07

[0627] In this embodiment, lithium cobalt oxide particles (manufactured by Nippon Chemical Industries, Ltd., trade name: C-20F) are used as the starting material.

[0628] Next, as step 14, lithium cobalt oxide particles were coated with titanium oxide using a sol-gel method and then dried. Step 14 was the same as in Example 1, except that the TTIP to lithium cobalt oxide ratio was mixed to be 0.004 ml / g. The lithium cobalt oxide particles coated with titanium oxide without heating were designated as Sample 06.

[0629] Next, the lithium cobalt oxide particles covered with titanium oxide, which were used as sample 06, were heated. This heating was carried out in a furnace under an oxygen atmosphere and at a temperature of 800°C, with the following conditions: holding time of 2 hours; oxygen flow rate of 10 L / min.

[0630] Then, as in Example 1, the particles were cooled and collected to obtain the positive electrode active material. The heated positive electrode active material is referred to as Sample 07.

[0631] [TEM-EDX]

[0632] TEM-EDX analysis was performed on samples 06 and 07, especially on and around the cracks that formed in the particles.

[0633] first, Figure 37A , Figure 37B1 , Figure 37B2 , Figure 37C1 , Figure 37C2 , Figure 37D1 , Figure 37D2 , Figure 37E1 , Figure 37E2 , Figure 38A , Figure 38B1 , Figure 38B2 , Figure 38C1 , Figure 38C2 , Figure 38D1 , Figure 38D2 , Figure 38E1 as well as Figure 38E2 The results of TEM-EDX surface analysis of titanium are shown.

[0634] Figure 37A , Figure 37B1 , Figure 37B2 , Figure 37C1 , Figure 37C2 , Figure 37D1 , Figure 37D2 , Figure 37E1 as well as Figure 37E2 The TEM-EDX analysis results of sample 06 before heating are shown. Figure 37A It is a cross-sectional TEM image showing the particle surface and cracks. Figure 37B1 and Figure 37B2 Shown separately in Figure 37A HAADF-STEM image and Ti distribution map of the region containing the particle surface, circled by 1. Similarly, Figure 37C1 and Figure 37C2 Shown separately in Figure 37A HAADF-STEM image and Ti distribution map of the region approximately 20 nm deep from the surface in the crack section circled in circle 2. Figure 37D1 and Figure 37D2 Shown separately in Figure 37A HAADF-STEM image and Ti distribution map of the region approximately 500 nm deep from the surface in the crack section circled in circle 3. Figure 37E1 and Figure 37E2 Shown separately in Figure 37A HAADF-STEM images and Ti distribution maps of the region approximately 1000 nm deep from the surface within the crack region circled in circle 4. Furthermore, in Figure 37A , Figure 37B1 , Figure 37B2 , Figure 37C1 , Figure 37C2 , Figure 37D1 , Figure 37D2 , Figure 37E1 , Figure 37E2 , Figure 38A , Figure 38B1 , Figure 38B2 , Figure 38C1 , Figure 38C2 , Figure 38D1 , Figure 38D2 , Figure 38E1 , Figure 38E2 , Figure 39A , Figure 39B1 , Figure 39B2 , Figure 39C1 , Figure 39C2, Figure 39D1 , Figure 39D2 , Figure 39E1 , Figure 39E2 , Figure 40A , Figure 40B1 , Figure 40B2 , Figure 40C1 , Figure 40C2 , Figure 40D1 , Figure 40D2 , Figure 40E1 as well as Figure 40E2 In the EDX element distribution map, white represents the number of elements below the detection limit, and the more elements there are, the closer the white area is to black.

[0635] Figure 38A , Figure 38B1 , Figure 38B2 , Figure 38C1 , Figure 38C2 , Figure 38D1 , Figure 38D2 , Figure 38E1 as well as Figure 38E2 The TEM-EDX analysis results of sample 07 after heating are shown. Figure 38A It is a cross-sectional TEM image showing the particle surface and cracks. Figure 38B1 and Figure 38B2 Shown separately in Figure 38A HAADF-STEM image and Ti distribution map of the region containing the particle surface, circled by 1. Similarly, Figure 38C1 and Figure 38C2 Shown separately in Figure 38A HAADF-STEM image and Ti distribution map of the region approximately 20 nm deep from the surface in the crack section circled in circle 2. Figure 38D1 and Figure 38D2 Shown separately in Figure 38A HAADF-STEM image and Ti distribution map of the region approximately 500 nm deep from the surface in the crack section circled in circle 3. Figure 38E1 and Figure 38E2 Shown separately in Figure 38A HAADF-STEM image and Ti distribution map of the region approximately 1000 nm deep from the surface in the crack section circled in circle 4.

[0636] like Figure 37A , Figure 37B1 , Figure 37B2 , Figure 37C1 , Figure 37C2 , Figure 37D1 , Figure 37D2 , Figure 37E1 , Figure 37E2 , Figure 38A , Figure 38B1 , Figure 38B2 , Figure 38C1 , Figure 38C2 , Figure 38D1 , Figure 38D2 , Figure 38E1 as well as Figure 38E2 As shown, in sample 06 before heating, titanium segregated on the particle surface was observed, but not in the crack portion. On the other hand, in sample 07 after heating, titanium segregated on both the particle surface and the crack portion was observed. This indicates that heating causes titanium segregation on the surface of the crack portion.

[0637] then, Figure 39A , Figure 39B1 , Figure 39B2 , Figure 39C1 , Figure 39C2 , Figure 39D1 , Figure 39D2 , Figure 39E1 , Figure 39E2 , Figure 40A , Figure 40B1 , Figure 40B2 , Figure 40C1 , Figure 40C2 , Figure 40D1 , Figure 40D2 , Figure 40E1 as well as Figure 40E2 The results of TEM-EDX surface analysis of magnesium are shown.

[0638] Figure 39A Is with Figure 37A Cross-sectional TEM image of the same sample 06. Figure 39B1 , Figure 39C1 , Figure 39D1 as well as Figure 39E1 Is with Figure 37B1 , Figure 37C1 , Figure 37D1 as well as Figure 37E1 The same HAADF-STEM image. Figure 39B2 Showing with Figure 39B1 Mg distribution map of the same region. Figure 39C2 Showing with Figure 39C1 Mg distribution map of the same region. Figure 39D2 Showing with Figure 39D1 Mg distribution map of the same region. Figure 39E2 Showing with Figure 39E1 Mg distribution map of the same region.

[0639] Figure 40A Is with Figure 38A Cross-sectional TEM image of the same sample 07. Figure 40B1 , Figure 40C1 , Figure 40D1 as well as Figure 40E1 Is with Figure 38B1 , Figure 38C1 , Figure 38D1 as well as Figure 38E1 The same HAADF-STEM image. Figure 40B2 Showing with Figure 40B1 Mg distribution map of the same region. Figure 40C2 Showing with Figure 40C1 Mg distribution map of the same region. Figure 40D2 Showing with Figure 40D1 Mg distribution map of the same region. Figure 40E2 Showing with Figure 40E1 Mg distribution map of the same region.

[0640] like Figure 39A , Figure 39B1 , Figure 39B2 , Figure 39C1 , Figure 39C2 , Figure 39D1 , Figure 39D2 , Figure 39E1 , Figure 39E2 , Figure 40A , Figure 40B1 , Figure 40B2 , Figure 40C1 , Figure 40C2 , Figure 40D1 , Figure 40D2 , Figure 40E1 as well as Figure 40E2 As shown, in sample 06 before heating, no magnesium segregation was observed on the particle surface or in the cracks. On the other hand, in sample 07 after heating, magnesium segregation was observed on both the particle surface and in the cracks.

[0641] Next, in order to quantify titanium and magnesium, the following steps were taken: Figure 37A The areas circled in the middle from 1 to 6 and in Figure 38A EDX point analysis was performed on the areas circled from 1 to 6. Two points were measured in each area.

[0642] Figure 41A and Figure 41B The results of EDX point analysis are shown in terms of the atomic ratio of titanium to cobalt. Figure 41A The results for sample 06 before heating are shown. Figure 41A Detection points 1 to 6 in the middle are equivalent to... Figure 37A The area circled in the middle with numbers 1 to 6. Figure 41B The results for sample 07 after heating are shown. Figure 41B Detection points 1 to 6 in the middle are equivalent to... Figure 38A The area circled in the middle with numbers 1 to 6.

[0643] like Figure 41A and Figure 41BAs shown, in the crack section of sample 06, the Ti / Co ratio at each measurement point is below 0.01. On the other hand, in the crack section of sample 07, the titanium content increases at multiple points, and there are also measurement points with a Ti / Co ratio of 0.05 or higher. Furthermore, the Ti / Co ratio on the particle surface of sample 07 is between 0.10 and 0.18.

[0644] then, Figure 42A and Figure 42B The results of EDX point analysis are shown in terms of the atomic ratio of magnesium to cobalt. Detection point and... Figure 41A and Figure 41B same.

[0645] like Figure 42A and Figure 42B As shown, in sample 06, the Mg / Co ratio on the particle surface and in the cracks is below 0.03. On the other hand, in sample 07, the magnesium content increases at multiple points on the particle surface and in the cracks. Furthermore, the Mg / Co ratio on the particle surface is between 0.15 and 0.50, and the Mg / Co ratio in the cracks is between 0 and 0.22.

[0646] Next, a coin-shaped secondary battery of CR2032 was fabricated using the heated positive electrode active material of sample 07. As the positive electrode, a slurry prepared by mixing the positive electrode active material (LCO) of sample 02, AB, and polyvinylidene fluoride (PVDF) in a weight ratio of 95:3:2 was coated onto the positive electrode current collector. As the positive electrode current collector, an aluminum foil with a thickness of 20 μm was used. The carrying capacity of the positive electrode active material layer containing the positive electrode active material, AB, and PVDF was 7.6 g / cm³. 2 .

[0647] Lithium metal is used as the counter electrode.

[0648] The electrolyte is prepared by dissolving 1 mol / L lithium hexafluorophosphate (LiPF6) in a solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, and adding 2 wt% vinylene carbonate (VC) to the solution.

[0649] [Initial characteristics, charge / discharge rate characteristics]

[0650] The initial characteristics and charge / discharge rate characteristics of a secondary battery using the positive electrode active material of sample 07 formed as described above were measured below.

[0651] In the initial characteristic determination, charging was performed under the conditions of CCCV, 0.2C, 4.6V, and 0.05C cutoff current, and discharging was performed under the conditions of CC, 0.2C, and 3.0V cutoff voltage. Here, 1C was set to 160mA / g, which is the current value per unit weight of the positive electrode active material. The measurement temperature was 25℃. Table 2 shows the measurement results of the initial characteristics.

[0652] [Table 2]

[0653]

[0654] After initial characteristics were measured, charge / discharge rate characteristics were determined. Measurements were performed by changing the discharge rate in the following order: 0.2C charge / 0.2C discharge; 0.2C charge / 0.5C discharge; 0.2C charge / 1.0C discharge; 0.2C charge / 2.0C discharge; 0.2C charge / 3.0C discharge; 0.2C charge / 4.0C discharge; and 0.2C charge / 5.0C discharge. Note that all conditions except the discharge rate were the same as those for the initial characteristics. The measurement temperature was 25°C.

[0655] Table 3 shows the measurement results of initial characteristics and charge / discharge rate characteristics. In addition, Figure 43 The discharge curves showing the charge / discharge rates are displayed.

[0656] [Table 3]

[0657]

[0658] [Temperature Characteristics]

[0659] Next, in addition to setting the holding capacity of the positive electrode active material layer to 8.2 mg / cm³, 2 The cell was manufactured under the same conditions as the cell used to evaluate the charge / discharge rate, except for the temperature characteristics, and its temperature characteristics were measured. Charging was performed at 25°C, CCCV, 0.2C, 4.6V, and a cutoff current of 0.05C. Discharging was then performed sequentially at temperatures of 25°C, 0°C, -10°C, -20°C, and 45°C, with cutoff voltages of CC, 0.2C, and 3.0V. Figure 44 The results of the temperature characteristics measurement are shown.

[0660] [Cyclic Characteristics]

[0661] Next, the cell was manufactured under the same conditions as the cell used to measure temperature characteristics, and its cycling characteristics were measured. In the cycling characteristic measurement, charging was performed at a cutoff current of 1.0C, 4.55V, and 0.05C, and discharging was performed at a cutoff voltage of 1.0C, 3.0V, and 45°C. The cycling characteristics were measured at 45°C for 100 cycles. The discharge capacity retention rate after 100 cycles was 86%. Figure 45 This is a graph showing the discharge capacity retention rate of the measured cycle characteristics.

[0662] The measurement results show that the specific surface area of ​​the positive electrode active material in sample 07 is 0.13 m². 2 / g.

[0663] Furthermore, the particle size distribution of the positive electrode active material in sample 07 shows that the average particle size is 21.5 μm, the 10% D is 13.1 μm, the 50% D is 22.0 μm, and the 90% D is 34.4 μm.

[0664] The bulk density of the positive electrode active material in sample 07 is 2.21 g / cm³. 3 The compaction density was measured using a MULTI TESTER MT-1000 (manufactured by SEISHIN ENTERPRISE Co., Ltd.).

[0665] Therefore, the positive electrode active material of Sample 07, as an embodiment of the present invention, exhibits superior initial charge-discharge capacity, charge-discharge rate characteristics, and cycle characteristics. In particular, the initial charge-discharge capacity is as high as 98% or more, and side reactions are suppressed. Furthermore, it also exhibits superior capacity even at a high discharge rate of 2C, i.e., 96.1% with reference to 0.2C.

[0666] [Example 3]

[0667] In this embodiment, by changing the ratio of Li to the first transition metal in the starting material, a positive electrode active material is formed in which the surface portion includes a region containing titanium and magnesium, and the evaluation results of the properties are shown.

[0668] [Formation of positive electrode active material]

[0669] In this embodiment, positive electrode active materials for samples 11 to 17, 21 to 28, and 31 to 40, using cobalt as the first transition metal, are prepared. The formation methods and conditions for each sample are shown below.

[0670] Samples 11 to 17

[0671] First, the lithium, cobalt, magnesium, and fluorine sources used as starting materials are weighed separately. In this embodiment, lithium carbonate, cobalt oxide, magnesium oxide, and lithium fluoride are used as the lithium, cobalt, magnesium, and fluorine sources, respectively.

[0672] At this point, the starting materials for sample 11 were weighed with a Li to Co ratio of 1.00. The starting materials for sample 12 were weighed with a Li to Co ratio of 1.03. The starting materials for sample 13 were weighed with a Li to Co ratio of 1.05. The starting materials for sample 14 were weighed with a Li to Co ratio of 1.06. The starting materials for sample 15 were weighed with a Li to Co ratio of 1.07. The starting materials for sample 16 were weighed with a Li to Co ratio of 1.08. The starting materials for sample 17 were weighed with a Li to Co ratio of 1.13.

[0673] In addition, the starting materials of samples 11 to 17 were weighed such that the number of magnesium atoms was 0.01 and the number of fluorine atoms was 0.02 when the number of cobalt atoms contained in the starting materials was set to 1.

[0674] Next, the starting materials of each weighed sample were mixed separately using a ball mill.

[0675] Next, the mixed starting materials were calcined. The calcination was carried out at 1000°C for 10 hours under the following conditions: temperature increase of 200°C / hour; and dry air flow rate of 10 L / min.

[0676] Through the above processes, particles containing composite oxides of lithium, cobalt, fluorine, and magnesium are synthesized.

[0677] Next, TTIP was added to 2-propanol at a concentration of 0.01 ml / g per unit weight of the positive electrode active material and mixed to form a 2-propanol solution of tetraisopropoxide titanium.

[0678] Particles containing composite oxides of lithium, cobalt, fluorine, and magnesium are added to a 2-propanol solution of TTIP and mixed.

[0679] The above mixture was stirred for 4 hours at 25°C and 90% RH using a magnetic stirrer. This treatment caused water in the atmosphere to undergo hydrolysis and condensation reactions with TTIP, thereby forming a titanium-containing layer on the surface of the lithium cobalt oxide particles containing magnesium and fluorine.

[0680] The treated mixture was filtered, and the residue was collected. Kiriyama filter paper (No. 4) was used as the filter.

[0681] The collected residue was dried in a vacuum at 70°C for 1 hour.

[0682] The dried particles were heated. The heating was carried out in an oxygen atmosphere under the following conditions: temperature 800°C (heating rate 200°C / hour); holding time 2 hours.

[0683] The heated particles are cooled and ground. The grinding process is carried out by sieving using a sieve with a pore size of 53 μm.

[0684] The particles that have been ground up were used as the positive electrode active material for samples 11 to 17.

[0685] Samples 21 to 27

[0686] The starting materials for samples 21 to 27 were the same as those for samples 11 to 16. In this case, the starting material for sample 21 was weighed with a Li to Co ratio of 1.00. The starting material for sample 22 was weighed with a Li to Co ratio of 1.03. The starting material for sample 23 was weighed with a Li to Co ratio of 1.05. The starting material for sample 24 was weighed with a Li to Co ratio of 1.06. The starting material for sample 25 was weighed with a Li to Co ratio of 1.07. The starting material for sample 26 was weighed with a Li to Co ratio of 1.08. The starting material for sample 27 was weighed with a Li to Co ratio of 1.13.

[0687] Samples 21 to 27 were formed under the same conditions as samples 11 to 17, except that the concentration of TTIP in the 2-propanol solution was set to 0.02 ml / g of the positive electrode active material per unit weight.

[0688] Sample 28

[0689] The ratio of Li to Co and the amount of TTIP in the starting material of Sample 28 are the same as those in Sample 23. That is, in Sample 28, the starting material was weighed with a Li to Co ratio of 1.05, and the TTIP per unit weight of the positive electrode active material was 0.02 ml / g.

[0690] Note that in sample 28, after the starting materials were mixed, the sample was calcined at a temperature of 950°C.

[0691] Sample 28 was formed under the same conditions as sample 23, except for the calcination temperature.

[0692] Samples 11 to 17 and samples 21 to 28 can be considered as positive electrode active materials containing lithium cobalt oxide internally and having regions containing titanium and magnesium on the surface.

[0693] Samples 31 to 40

[0694] As a comparative example, samples 31 to 40 were formed in a manner that did not include the region containing titanium.

[0695] The starting materials for sample 31 were weighed at a Li:Co ratio of 1.00. The starting materials for sample 32 were weighed at a Li:Co ratio of 1.01. The starting materials for sample 33 were weighed at a Li:Co ratio of 1.02. The starting materials for sample 34 were weighed at a Li:Co ratio of 1.03. The starting materials for sample 35 were weighed at a Li:Co ratio of 1.035. The starting materials for sample 36 were weighed at a Li:Co ratio of 1.04. The starting materials for sample 37 were weighed at a Li:Co ratio of 1.051. The starting materials for sample 38 were weighed at a Li:Co ratio of 1.061. The starting materials for sample 39 were weighed at a Li:Co ratio of 1.081. The starting materials for sample 40 were weighed at a Li:Co ratio of 1.130.

[0696] In addition, the starting materials of samples 31 to 40 were weighed such that the number of magnesium atoms was 0.01 and the number of fluorine atoms was 0.02 when the number of cobalt atoms contained in the starting materials was set to 1.

[0697] Next, the starting materials of each weighed sample were mixed separately using a ball mill.

[0698] Next, the mixed starting materials were calcined. The calcination was carried out at 1000°C for 10 hours under the following conditions: temperature increase of 200°C / hour; and dry air flow rate of 10 L / min.

[0699] Through the above processes, particles containing composite oxides of lithium, cobalt, fluorine, and magnesium are synthesized.

[0700] The synthesized particles were cooled and then heated. The heating was carried out in an oxygen atmosphere under the following conditions: temperature 800℃ (heating rate 200℃ / hour); holding time 2 hours.

[0701] The heated particles are cooled and ground. The grinding process is carried out by sieving using a sieve with a pore size of 53 μm.

[0702] The particles that have been ground up were used as the positive electrode active material for samples 31 to 40.

[0703] Table 4 shows the formation conditions of samples 11 to 17, 21 to 28, and 31 to 40.

[0704] [Table 4]

[0705]

[0706]

[0707] [XPS]

[0708] XPS analysis was performed on the positive electrode active materials of samples 11 to 17, 21 to 28, and 31 to 40. Table 5 shows the XPS analysis results for samples 11 to 17, Table 6 shows the XPS analysis results for samples 21 to 28, and Table 7 shows the XPS analysis results for samples 31 to 40. Tables 5 to 7 show the relative concentrations of each element when the cobalt concentration is 1.

[0709] [Table 5]

[0710]

[0711] [Table 6]

[0712]

[0713] [Table 7]

[0714]

[0715] Figure 46A and Figure 46B This is a graph showing the relative values ​​of magnesium and titanium extracted from the analysis results in Tables 5 to 7. Figure 46A This is a graph showing the ratio of Li to Co and the relative values ​​of magnesium. Figure 46B This is a graph showing the ratio of Li to Co versus the relative value of titanium.

[0716] Depend on Figure 46A As shown in samples 31 to 40, in the absence of a titanium-containing coating, samples with a Li to Co ratio of 1.00 or higher but less than 1.05 exhibit high magnesium concentrations. This is because magnesium contained in the starting material segregates upon heating to a level where its elemental concentration can be detected by XPS. Conversely, samples with a Li to Co ratio of 1.06 or higher show low magnesium concentrations, indicating that magnesium segregation is less likely to occur when the amount of lithium is too high.

[0717] Depend on Figure 46AAs can be seen from samples 11 to 16 and samples 21 to 26, the magnesium concentration is higher when the surface layer contains titanium regions than when there are no titanium regions. The concentration of these titanium regions is detectable by XPS.

[0718] Furthermore, when the Li to Co ratio is 1.06, the magnesium concentration in the sample excluding the titanium-containing region is low to the extent that the elemental concentration can be detected by XPS, while the magnesium concentration in the sample including the titanium-containing region is high to the extent that the elemental concentration can be detected by XPS. In other words, by forming a titanium-containing region on the surface, magnesium segregation is very easy to occur even when the Li to Co ratio is high.

[0719] Note that even including regions containing titanium, the magnesium concentration at a Li to Co ratio of 1.07 is lower than that at a Li to Co ratio of 1.06. Furthermore, it is also known that even including regions containing titanium, magnesium segregation is less likely to occur at Li to Co ratios of 1.08 or higher.

[0720] [Evaluation of Cyclic Characteristics]

[0721] Energy density retention rate

[0722] Next, the positive electrode active materials of samples 11 to 14, 16, 21 to 24 and 26 were evaluated for their cycling characteristics in the same manner as in Example 1.

[0723] The shape of the secondary battery, the positive electrode active material in the positive electrode, the conductive additives and the materials and mixing ratio of the binder, the counter electrode, the electrolyte, the outer packaging, and the conditions for cycle characteristic testing are the same as in Example 1.

[0724] Figure 47A The graph shows the energy density retention and charge-discharge cycle number of secondary batteries using positive electrode active materials prepared in a manner with a TTIP of 0.01 ml / g per unit weight of positive electrode active material, when charged at 4.6V. Figure 47B The graph shows the energy density retention and charge-discharge cycle number of secondary batteries using positive electrode active materials of samples 21 to 24 and sample 26, which were prepared with a TTIP of 0.02 ml / g per unit weight of positive electrode active material, when charged at 4.6V.

[0725] Depend on Figure 47AIt can be seen that, with a TTIP of 0.01 ml / g, samples 11 to 14, i.e., the positive electrode active materials with a Li to Co ratio of 1.00 or higher and 1.06 or lower, exhibit superior cycling characteristics. In particular, samples 11 and 12, i.e., the positive electrode active materials with a Li to Co ratio of 1.00 or higher and 1.03 or lower, exhibit extremely superior cycling characteristics. Conversely, in sample 16, with a Li to Co ratio of 1.08, the energy density retention rate decreases in the earlier stages.

[0726] Depend on Figure 47B It can be seen that, with a TTIP of 0.02 ml / g, samples 21 to 24, i.e., the positive electrode active materials with a Li to Co ratio of 1.00 or higher and 1.06 or lower, exhibit superior cycling characteristics. In particular, samples 23 and 24, i.e., the positive electrode active materials with a Li to Co ratio of 1.05 or higher and 1.06 or lower, exhibit extremely superior cycling characteristics.

[0727] Figure 48 This is a graph showing a comparison between sample 11, which exhibits the best cycling characteristics among samples 11 to 15, and sample 23, which exhibits the best cycling characteristics among samples 21 to 25.

[0728] Depend on Figure 48 It can be seen that both Sample 11 and Sample 23 exhibit extremely superior cycling characteristics. In particular, Sample 23, with a TTIP of 0.02 ml / g, exhibits even better cycling characteristics.

[0729] Discharge Capacity Retention Rate

[0730] then, Figure 49 The evaluation results of discharge capacity retention, one of the cycle characteristics of samples 21 to 26 and sample 28, are shown.

[0731] The shape of the secondary batteries in samples 21 to 26, the positive electrode active material in the positive electrode, the conductive additives and the materials and mixing ratio of the binder, the counter electrode, the electrolyte, the outer packaging, and the conditions for cycle characteristic testing are the same as in Example 1.

[0732] The secondary battery using sample 28 was formed under the same conditions as the secondary batteries using samples 21 to 26, except that PVDF was used as a binder and mixed with positive electrode active material (LCO):AB:PVDF in a weight ratio of 95:3:2, and was evaluated.

[0733] Depend on Figure 49 It can be seen that samples 21 to 24 and sample 28 exhibit excellent cycling characteristics. In particular, sample 28 exhibits extremely superior cycling characteristics. In sample 28, the discharge capacity retention rate is more than 85% after 50 cycles.

[0734] Conversely, in samples 25 and 26 with Li to Co ratios of 1.07 and 1.08, the discharge capacity retention decreased in the earlier stages.

[0735] The results above show that, with a TTIP of 0.02 ml / g per unit weight of the positive electrode active material, the preferred Li to Co ratio is between 1.00 and 1.07. Furthermore, samples with a Li to Co ratio between 1.05 and 1.06 exhibit extremely superior cycling characteristics.

[0736] Figures 50A to 50C Showing the use in Figure 49 Charge-discharge curves of secondary batteries of samples 28 and 24, which exhibit extremely superior cycle characteristics, and sample 25, which deteriorates in an earlier stage.

[0737] Figures 50A to 50C The charge-discharge curves for the secondary batteries using samples 28, 24, and 25 are shown respectively. Each curve shows the overlap of the results after 50 charge-discharge cycles. As indicated by the arrows in the curves, the charge-discharge capacity decreases from cycle 1 to cycle 50.

[0738] like Figure 50A and Figure 50B As shown, samples 28 and 24, which are positive electrode active materials according to one embodiment of the present invention, have high charge-discharge capacity and excellent charge-discharge characteristics. Furthermore, with... Figure 50C Compared to sample 25, Figure 50A and Figure 50B The reduction in charge and discharge capacity of samples 28 and 24 was significantly suppressed.

[0739] [Example 4]

[0740] In this embodiment, the SEM observation results and SEM-EDX analysis results of the positive electrode active material of sample 24 formed in Example 2 are described.

[0741] Sample 24 was formed with a Li to Co ratio of 1.06 and a TTIP of 0.02 ml / g per unit weight of positive electrode active material. Figure 51A The SEM image of sample 24 is shown. Figure 51B and Figure 51C Show Figure 51A A magnified image of a portion of the image.

[0742] like Figures 51A to 51C As shown, there are multiple convex regions on the surface of the positive electrode active material.

[0743] then, Figure 52A-1 , Figure 52A-2 , Figure 52B-1 , Figure 52B-2 , Figure 52C-1 as well as Figure 52C-2 The results of SEM-EDX analysis of the positive electrode active material of sample 24 are shown. Figure 52A-1 The image shows an SEM image of the surface layer of the positive electrode active material. Figure 52A-2 The distribution map of titanium is shown. Figure 52B-1 The distribution map of magnesium is shown. Figure 52B-2 The distribution of oxygen is shown in the diagram. Figure 52C-1 The distribution map of aluminum is shown, and Figure 52C-2 A distribution map of cobalt is shown. Furthermore, in Figure 52A-2 , Figure 52B-1 , Figure 52B-2 , Figure 52C-1 as well as Figure 52C-2 In the EDX element distribution map, black represents the number of elements below the detection limit, and the more elements there are, the closer the black area is to white.

[0744] Figure 52A-1 , Figure 52A-2 , Figure 52B-1 The same area is surrounded by a dashed line. When comparing the areas surrounded by dashed lines, it can be seen that titanium and magnesium are distributed in the convex region of the surface layer of the positive electrode active material.

[0745] Therefore, it can be seen that sample 24 is a positive electrode active material that includes a convex fourth region 104 containing titanium and magnesium on the third region 103.

[0746] As shown in Example 2, Sample 24 is one of the samples exhibiting extremely superior cycle characteristics. Therefore, even when a fourth region is provided on the surface of the positive electrode active material, or when a fourth region is provided, a positive electrode active material exhibiting superior cycle characteristics can be obtained.

[0747] As can be seen from the results of Examples 1 to 3 above, by forming a titanium-containing region in the surface layer, a positive electrode active material exhibiting superior cycle characteristics is obtained. It is also known that while increasing the Li to Co ratio to increase the particle size of the positive electrode active material may degrade cycle characteristics, forming a titanium-containing region in the surface layer can broaden the range of Li to Co ratios from which superior cycle characteristics can be obtained. Furthermore, even when a fourth region containing titanium and magnesium is provided in the surface layer of the positive electrode active material, superior cycle characteristics can still be obtained.

[0748] [Example 5]

[0749] In this embodiment, an example of a method for manufacturing a positive electrode active material covered with graphene oxide is shown, and electron microscopic observations of the positive electrode active material prepared using this method are illustrated.

[0750] like Figure 53 As shown in the process flow diagram, the process of forming a coating film on the positive electrode active material includes the following steps: weighing graphene oxide (S11); mixing and stirring graphene oxide and pure water (S12); pH control (S13); adding active material (S14); completing the suspension (S15); spraying the suspension using a spray drying device (S16); and collecting particles in the container (S17).

[0751] Note that although pure water is used as the dispersion medium in (S12), there are no particular restrictions on the dispersion medium; ethanol or other substances can also be used. Furthermore, in (S14), the active material is the positive electrode active material.

[0752] Figure 54 This is a schematic diagram of a spray drying apparatus 280. The spray drying apparatus 280 includes a processing chamber 281 and a nozzle 282. A suspension 284 is supplied to the nozzle 282 through a pipe 283. The suspension 284 is supplied from the nozzle 282 in a spray form to the processing chamber 281, where drying takes place. Alternatively, a heater 285 can be used to heat the nozzle 282. Here, the heater 285 can also be used to heat the area in the processing chamber 281 closest to the nozzle 282, for example... Figure 54 The area surrounded by double-dotted lines.

[0753] When using a suspension containing positive electrode active material and graphene oxide as suspension 284, the powder of positive electrode active material covered with graphene oxide is collected in container 286 through processing chamber 281.

[0754] The air in the processing chamber 281 can also be extracted using an air extractor or similar device via the path indicated by arrow 288.

[0755] The following shows the conditions for forming the coating film.

[0756] First, graphene oxide is dispersed in a solvent to form a suspension.

[0757] Graphene oxide exhibits high dispersibility in pure water; however, pure water may react with subsequently added active materials, causing Li to dissolve or damaging the active materials to the point of altering their surface structure. Therefore, graphene oxide was dispersed in a solution with ethanol and pure water in a ratio of 4:6.

[0758] To disperse graphene oxide in the solution, stirring was performed under the following conditions: a magnetic stirrer and an ultrasonic generator were used; the stirring speed was 750 rpm; and the ultrasonic irradiation time was 2 minutes.

[0759] Then, add LiOH aqueous solution dropwise to adjust the pH to pH 7 (25°C).

[0760] The positive electrode active material (in this embodiment, lithium cobalt oxide particles manufactured by Nippon Chemical Industries Co., Ltd. (trade name: C-20F)) was added, and the mixture was stirred using a magnetic stirrer and an ultrasonic generator under the following conditions: a rotation speed of 750 rpm; and an ultrasonic irradiation time of 1 minute. A suspension was prepared through the above steps. The lithium cobalt oxide particles (trade name: C-20F) manufactured by Nippon Chemical Industries Co., Ltd. contain at least fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus, and have a particle size of approximately 20 μm.

[0761] Next, the suspension was uniformly sprayed using the nozzle (20 μm diameter) of the spray drying equipment to obtain powder. The inlet temperature of the spray drying equipment was 160°C, the outlet temperature was 40°C, and the N2 gas flow rate was 10 L / min.

[0762] Figure 55 A cross-sectional TEM image of the obtained powder is shown. Furthermore, Figure 56 SEM images of the obtained powder are shown. When, as a comparative example, the same positive electrode active material (C-20F manufactured by Nippon Chemical Industries Co., Ltd.) and graphene oxide were mixed using a rotary mixer, the coating was insufficient. Figure 57 SEM images showing comparative examples are provided.

[0763] Therefore, it can be concluded that, with Figure 57 In comparison, Figure 56 The coating film is uniformly formed on the surface of the powder.

[0764] Figure 58A and Figure 58B An example cross-sectional structure of an active material layer 200, which is coated with graphene oxide using a spray drying device and contains a graphene compound as a conductive agent, is shown.

[0765] Figure 58A This is a longitudinal cross-sectional view of the active material layer 200. The active material layer 200 includes granular positive electrode active material 100 covered with graphene oxide, graphene compound 201 used as a conductive additive, and a binder (not shown). Here, as the graphene compound 201, graphene or multilayer graphene can be used, for example. Furthermore, the graphene compound 201 is preferably in a sheet-like form. The graphene compound 201 can be formed into a sheet by partially overlapping multiple multilayer graphene or / and multiple monolayer graphene.

[0766] In the longitudinal section of the active material layer 200, such as Figure 58BAs shown, the positive electrode active material 100 covered by the coating film 105 is in contact with the graphene compound 201. Multiple graphene compounds 201 are formed in such a way that they are partially in contact with the positive electrode active material 100 covered by the coating film 105 and adhere to the coating film 105 of adjacent positive electrode active materials 100, so that multiple graphene compounds 201 are in contact with each positive electrode active material 100.

[0767] Both the graphene compound 201 and the coating film 105 are formed from carbon-based materials, which allows for the formation of a superior conductive path.

[0768] The coating 105 has the effect of protecting the crystal structure of the positive electrode active material 100 from contact with the electrolyte and forming a superior conductive path.

[0769] Symbol Explanation

[0770] 11a: Positive electrode, 11b: Negative electrode, 12a: Wire, 12b: Wire, 14: Insulator, 15a: Junction, 15b: Junction, 17: Fixing component, 50: Secondary battery, 51: Outer packaging, 61: Folded part, 62: Sealing part, 63: Sealing part, 71: Ridge, 72: Valley line, 73: Space, 100: Positive electrode active material, 101: First region, 101p: Crystal plane, 102: Second region, 102p: Crystal plane, 103: Third region, 103p: Crystal plane, 104: Fourth region, 105: Coating film, 106: Crack, 110: Particle, 111: Region, 112: Titanium-containing layer, 114: Cobalt oxide layer, 120: Particle, 121: Region Domain, 122: Titanium-containing layer, 124: Cobalt oxide layer, 125: Lithium titanate-containing layer, 200: Active material layer, 201: Graphene compound, 214: Separator, 280: Spray drying equipment, 281: Processor, 282: Nozzle, 283: Tube, 284: Suspension, 285: Heater, 286: Container, 288: Arrow, 300: Coin-type secondary battery, 301: Positive electrode container, 302: Negative electrode container, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Separator, 500: Laminated secondary battery, 501: Positive electrode current collector. 502: Positive electrode active material layer; 503: Positive electrode; 504: Negative electrode current collector; 505: Negative electrode active material layer; 506: Negative electrode; 507: Insulator; 508: Electrolyte; 509: Outer packaging; 510: Positive electrode wire; 511: Negative electrode wire; 600: Cylindrical secondary battery; 601: Positive electrode cap; 602: Battery can; 603: Positive terminal; 604: Positive electrode; 605: Insulator; 606: Negative electrode; 607: Negative terminal; 608: Insulating plate; 609: Insulating plate; 611: PTC element; 612: Safety valve mechanism; 613: Conductive plate; 614: Conductive plate; 615: Module; 616: Wire; 617: Temperature control device; 900: Circuit board. 910: Label, 911: Terminal, 912: Circuit, 913: Secondary battery, 914: Antenna, 915: Antenna, 916: Layer, 917: Layer, 918: Antenna, 920: Display device, 921: Sensor, 922: Terminal, 930: Frame, 930a: Frame, 930b: Frame, 931: Negative electrode, 932: Positive electrode, 933: Insulator, 950: Wound body, 951: Terminal, 952: Terminal, 980: Laminated secondary battery, 981: Thin film, 982: Thin film, 993: Wound body, 994: Negative electrode, 995: Positive electrode, 996: Insulator, 997: Wire electrode, 998: Wire electrode, 7100: Portable display device, 7101: Frame.7102: Display unit, 7103: Operation button, 7104: Secondary battery, 7200: Portable information terminal, 7201: Frame, 7202: Display unit, 7203: Strap, 7204: Buckle, 7205: Operation button, 7206: Input / output terminal, 7207: Icon, 7300: Display device, 7304: Display unit, 7400: Mobile phone, 7401: Frame, 7402: Display unit, 7403: Operation button, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7 407: Secondary battery; 7408: Lead electrode; 7409: Current collector; 7500: Electronic cigarette; 7501: Atomizer; 7502: Cartridge; 7504: Secondary battery; 8000: Display device; 8001: Frame; 8002: Display section; 8003: Speaker section; 8004: Secondary battery; 8021: Ground-mounted charging device; 8022: Cable; 8024: Secondary battery; 8100: Lighting device; 8101: Frame; 8102: Light source; 8103: Secondary battery; 8104: Ceiling; 810 5: Side wall; 8106: Floor; 8107: Window; 8200: Indoor unit; 8201: Frame; 8202: Air outlet; 8203: Secondary battery; 8204: Outdoor unit; 8300: Electric refrigerator / freezer; 8301: Frame; 8302: Refrigerator door; 8303: Freezer door; 8304: Secondary battery; 8400: Automobile; 8401: Headlight; 8406: Electric motor; 8500: Automobile; 8600: Motorcycle; 8601: Rearview mirror; 8602: Secondary battery; 8603: Turn signal; 860... 4: Under-seat storage box; 9600: Tablet terminal; 9625: Power-saving mode switch; 9626: Display mode switch; 9627: Power switch; 9628: Operation switch; 9629: Fastener; 9630: Frame; 9630a: Frame; 9630b: Frame; 9631: Display unit; 9631a: Display unit; 9631b: Display unit; 9633: Solar cell; 9634: Charging / discharging control circuit; 9635: Battery; 9636: DC-DC converter; 9637: Converter; 9640: Movable part.

[0771] This application is based on Japanese Patent Application No. 2016-133997, filed with the Japan Patent Office on July 6, 2016; Japanese Patent Application No. 2016-133143, filed with the Japan Patent Office on July 5, 2016; Japanese Patent Application No. 2017-002831, filed with the Japan Patent Office on January 11, 2017; Japanese Patent Application No. 2017-030693, filed with the Japan Patent Office on February 22, 2017; Japanese Patent Application No. 2017-084321, filed with the Japan Patent Office on April 21, 2017; and Japanese Patent Application No. 2017-119272, filed with the Japan Patent Office on June 19, 2017, the entire contents of which are incorporated herein by reference.

Claims

1. A method for manufacturing a lithium-ion secondary battery, the lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode active material, the method comprising the following steps: A composite oxide is coated with a titanium-containing material, the composite oxide comprising lithium, cobalt, magnesium, and fluorine; and The composite oxide is heated at a temperature above 800°C and below 1000°C. in, The heating step causes titanium to segregate in the cracks of the positive electrode active material.

2. A method for manufacturing a lithium-ion secondary battery, the lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode active material, the method comprising the following steps: A composite oxide is coated with a titanium-containing material, the composite oxide comprising lithium, cobalt, magnesium, and fluorine; and The composite oxide is heated at a temperature above 800°C and below 1000°C. in, Magnesium segregates in the cracks of the positive electrode active material during the heating step.

3. A method for manufacturing a lithium-ion secondary battery, the lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode active material, the method comprising the following steps: A composite oxide is coated with a titanium-containing material, the composite oxide comprising lithium, cobalt, magnesium, and fluorine; and The composite oxide is heated at a temperature above 800°C and below 1000°C. in, The heating step forms regions containing titanium and magnesium within the cracks of the positive electrode active material. Furthermore, the crack is repaired by utilizing the presence of the area described above.

4. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, The heating step is carried out in an atmosphere containing oxygen.

5. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, The step of covering with a titanium-containing material is performed by a sol-gel method.

6. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, The cracked portion is the area in contact with the electrolyte.

7. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, Fluorine segregates in the cracks through the heating step.

8. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, During the heating step, the distribution of magnesium overlaps with the distribution of titanium.

9. The method for manufacturing a lithium-ion secondary battery according to any one of claims 1 to 3, In the heating step, the distribution of magnesium and titanium overlaps in the line analysis of energy-dispersive X-ray analysis.

Images