Positive electrode active material particle and method for manufacturing positive electrode active material particle

Abstract

The present disclosure is "positive electrode active material particles and a method for manufacturing positive electrode active material particles". A positive electrode active material that suppresses capacity reduction due to charge and discharge cycles when used in a lithium ion secondary battery is provided. A covering layer is formed by segregation at a surface layer portion of the positive electrode active material. The positive electrode active material includes a first region and a second region. The first region is present in the inside of the positive electrode active material. The second region is present in a part of the surface layer portion and the inside of the positive electrode active material. The first region contains lithium, a transition metal, and oxygen. The second region contains magnesium, fluorine, and oxygen.

Description

Technical Field

[0001] One embodiment of the present invention relates to an article, method, or manufacturing method. The present invention relates to a process, machine, manufacture, or composition of matter. 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.

[0002] In this specification, the term "energy storage device" refers to a general term for components and devices that have the function of storing electricity. For example, batteries such as lithium-ion secondary batteries (also called rechargeable batteries), lithium-ion capacitors, and double-layer capacitors are included in the scope of energy storage devices.

[0003] Note that 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

[0004] In recent years, research and development of various energy storage devices, such as lithium-ion rechargeable batteries, lithium-ion capacitors, and air batteries, has become increasingly active. In particular, with the development of the semiconductor industry for portable information terminals such as mobile phones, smartphones, and laptop computers, portable music players, digital cameras, medical equipment, and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs), the demand for high-output, high-capacity lithium-ion rechargeable batteries has surged. As a rechargeable energy source, lithium-ion rechargeable batteries have become an indispensable item in modern information society.

[0005] The characteristics currently required for lithium-ion rechargeable batteries include: large capacity, improved cycle performance, safe operation in various environments, and long-term reliability.

[0006] One known method to increase the capacity of lithium-ion secondary batteries is to increase the charging voltage. For example, when the charging voltage is 4.3V, the capacity of lithium cobalt oxide, which is commonly used as the positive electrode active material in lithium-ion secondary batteries, is 155mAh / g, while it increases to 220mAh / g when the charging voltage is increased to 4.6V (see reference). Figure 21A ).

[0007] However, it is known that increasing the charging voltage leads to a deterioration in cycle characteristics. For example, typically, when the charging voltage is 4.4V, the capacity retention of lithium cobalt oxide is above 95% after 30 cycles; however, when the charging voltage is increased to 4.6V, the capacity retention drops to below 50% after 30 cycles (see reference). Figure 21B ).

[0008] Therefore, improvements to the positive electrode active material are being reviewed in order to improve the cycle characteristics and capacity of lithium-ion secondary batteries (Patent Document 1 and Patent Document 2).

[0009] [Patent Literature]

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

[0011] [Patent Document 2] Japanese Patent Application Publication No. 2016-076454 Summary of the Invention

[0012] Thus, the development of lithium-ion secondary batteries and the positive electrode active materials used in them is influenced by improvements in various aspects such as capacity, cycle characteristics, charge and discharge characteristics, reliability, safety, and cost.

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

[0014] Another object of one embodiment of the present invention is to provide a novel substance, active substance, energy storage device or method of manufacturing the same.

[0015] Note that the description of the above objectives does not preclude the existence of other objectives. In one embodiment of the invention, it is not necessary to achieve all of the above objectives. Objectives other than those described above can be extracted from the description, drawings, and claims.

[0016] To achieve the above objectives, one embodiment of the present invention is characterized in that a covering layer is formed on the surface of the positive electrode active material by segregation.

[0017] One embodiment of the present invention is a positive electrode active material. The positive electrode active material includes a first region and a second region. The first region exists within the interior of the positive electrode active material. The second region exists on the surface of the positive electrode active material and in a portion of its interior. The first region contains lithium, a transition metal, and oxygen. The second region contains magnesium, fluorine, and oxygen.

[0018] One embodiment of the present invention is a positive electrode active material. This positive electrode active material comprises lithium, a transition metal, oxygen, magnesium, and fluorine. The total atomic weight of lithium, transition metal, oxygen, magnesium, and fluorine on the surface of the positive electrode active material, as measured by X-ray photoelectron spectroscopy, is set to 100 atomic%. The magnesium concentration on the surface of the positive electrode active material, as measured by X-ray photoelectron spectroscopy, is 1 atomic% or more and 16 atomic% or less. The fluorine concentration on the surface of the positive electrode active material, as measured by X-ray photoelectron spectroscopy, is 0.2 atomic% or more and 4 atomic% or less.

[0019] One embodiment of the present invention is a positive electrode active material. This positive electrode active material comprises lithium, a transition metal, oxygen, magnesium, and fluorine. The ratio of magnesium concentration to fluorine concentration on the surface of the positive electrode active material, measured by X-ray photoelectron spectroscopy, is Mg:F = y:1 (3 ≤ y ≤ 5).

[0020] One embodiment of the present invention is a positive electrode active material. This positive electrode active material comprises lithium, a transition metal, oxygen, magnesium, and fluorine. The peak position of the fluorine bond energy on the surface of the positive electrode active material, measured by X-ray photoelectron spectroscopy, is above 682 eV and below 685 eV.

[0021] In the above structure, the transition metal preferably includes cobalt. Alternatively, the transition metal preferably includes manganese, cobalt, and nickel.

[0022] One embodiment of the present invention is a positive electrode active material comprising a first region and a second region. The first region exists within the positive electrode active material. The first region contains lithium, transition metals, and oxygen. The first region has a layered rock salt-type crystalline structure. The second region exists on the surface of the positive electrode active material and in a portion of its interior. The second region contains magnesium, fluorine, and oxygen. The second region also has a rock salt-type crystalline structure. The crystal orientations of the first and second regions are aligned. The ratio of magnesium concentration to fluorine concentration on the surface of the positive electrode active material, measured by X-ray photoelectron spectroscopy, is Mg:F = y:1 (3 ≤ y ≤ 5).

[0023] In the above structure, the peak position of the fluorine bond energy on the surface of the positive electrode active material, as measured by X-ray photoelectron spectroscopy, is preferably above 682 eV and below 685 eV.

[0024] One embodiment of the present invention is a method for manufacturing a positive electrode active material, comprising: a mixing step of a lithium source, a transition metal source, a magnesium source, and a fluorine source; a heating step at a temperature of 800°C or higher and 1100°C or lower for 2 hours or higher and 20 hours or lower; and a heating step in an oxygen-containing atmosphere at a temperature of 500°C or higher and 1200°C or lower for a holding time of 50 hours or lower. The atomic ratio of fluorine in the fluorine source to magnesium in the magnesium source is Mg:F = 1:x (1.5 ≤ x ≤ 4).

[0025] One embodiment of the present invention is a positive electrode active material comprising a first region and a second region. The first region exists within the positive electrode active material. The first region contains lithium, cobalt, and oxygen. The second region contains cobalt, magnesium, fluorine, and oxygen. When the positive electrode active material is measured using electron energy loss spectroscopy, the L3 / L2 ratio of cobalt contained in the first region is less than 3.8, and the L3 / L2 ratio of cobalt contained in the second region is greater than 3.8.

[0026] According to one embodiment of the present invention, a positive electrode active material that suppresses capacity reduction due to charge-discharge cycles when used in a lithium-ion secondary battery can be provided. Additionally, a high-capacity secondary battery can be provided. Furthermore, a secondary battery with good charge-discharge characteristics can be provided. Furthermore, a secondary battery with high safety or reliability can be provided. Additionally, novel materials, active materials, energy storage devices, or methods for manufacturing the same can be provided. Attached Figure Description

[0027] Figures 1A to 1C Provide examples of positive electrode active materials.

[0028] Figure 2 Examples illustrating the manufacturing methods of positive electrode active materials.

[0029] Figure 3A and Figure 3B This is a cross-sectional view of the active material layer containing graphene compounds as a conductive additive.

[0030] Figure 4A and Figure 4B Explanation of coin-type secondary batteries.

[0031] Figures 5A to 5D Explanation of cylindrical secondary batteries.

[0032] Figure 6A and Figure 6B An example illustrating a secondary battery.

[0033] Figures 7A1 to 7B2 An example illustrating a secondary battery.

[0034] Figure 8A and Figure 8BAn example illustrating a secondary battery.

[0035] Figure 9 An example illustrating a secondary battery.

[0036] Figures 10A to 10C Explain the laminated secondary battery.

[0037] Figure 11A and Figure 11B Explain the laminated secondary battery.

[0038] Figure 12 This is the appearance of a secondary battery.

[0039] Figure 13 This is the appearance of a secondary battery.

[0040] Figures 14A to 14C Explain the manufacturing method of secondary batteries.

[0041] Figures 15A to 15D Explain the concept of a flexible secondary battery.

[0042] Figure 16A and Figure 16B Explain the concept of a flexible secondary battery.

[0043] Figures 17A to 17G Examples of electronic devices.

[0044] Figures 18A to 18C Examples of electronic devices.

[0045] Figure 19 Examples of electronic devices.

[0046] Figures 20A to 20C Examples of electronic devices.

[0047] Figure 21A and Figure 21B Explain the characteristics of existing secondary batteries.

[0048] Figures 22A to 22C These are STEM images and EDX surface analysis images (EDX mapping) of the positive electrode active material in Example 1.

[0049] Figures 23A to 23C These are STEM images and EDX surface analysis images of the positive electrode active material of Example 1.

[0050] Figure 24 This is a graph showing the amount of magnesium near the surface of the positive electrode active material in Example 1.

[0051] Figure 25A and Figure 25B This is a graph showing the cycle characteristics of the secondary battery of Example 1.

[0052] Figure 26 This is a graph showing the cycle characteristics of the secondary battery of Example 1.

[0053] Figure 27 This is a graph showing the cycle characteristics of the secondary battery of Example 1.

[0054] Figure 28A and Figure 28B This is a graph showing the cycle characteristics of the secondary battery of Example 1.

[0055] Figure 29A and Figure 29B This is a STEM image of the positive electrode active material of Example 2.

[0056] Figure 30A and Figure 30B This is a STEM image of the positive electrode active material of Example 2.

[0057] Figures 31A to 31C This is a graph showing the charge and discharge characteristics of the secondary battery of Example 2.

[0058] Figure 32A and Figure 32B This is a graph showing the cycle characteristics of the secondary battery of Example 2.

[0059] Figures 33A to 33C These are STEM and FFT images of the positive electrode active material of Example 3.

[0060] Figures 34A to 34C These are STEM and FFT images of the positive electrode active material of Example 3.

[0061] Figures 35A to 35C These are STEM images and EDX surface analysis images of the positive electrode active material of Example 3.

[0062] Figure 36 This is a TEM image of the positive electrode active material of Example 3.

[0063] Figures 37A1 to 37B2 These are STEM images and EDX surface analysis images of the positive electrode active material of Example 3.

[0064] Figure 38 ToF-SIMS depth orientation analysis of the positive electrode active material in Example 3 is explained.

[0065] Figure 39 The XPS spectrum of the positive electrode active material in Example 3 is shown.

[0066] Figure 40A and Figure 40B This is a graph showing the cycle characteristics of the secondary battery of Example 4.

[0067] Figures 41A to 41C This is a graph showing the cycle characteristics of the secondary battery of Example 4.

[0068] Figures 42A to 42C This is a graph showing the cycle characteristics of the secondary battery of Example 4.

[0069] Figure 43A and Figure 43B This is a graph showing the cycle characteristics of the secondary battery of Example 6.

[0070] Figure 44A and Figure 44B This is a STEM image of the positive electrode active material of Example 6.

[0071] Figure 45A and Figure 45B This is a STEM image of the positive electrode active material of Example 6.

[0072] Figures 46A to 46D These are STEM and FFT images of the positive electrode active material of Example 6.

[0073] Figure 47 These are STEM images and a speculative model of the crystal structure of the positive electrode active material in Example 6.

[0074] Figures 48A1 to 48B2 These are STEM images and EDX surface analysis images of the positive electrode active material of Example 6.

[0075] Figures 49A1 to 49B2 These are STEM images and EDX surface analysis images of the positive electrode active material of Example 6.

[0076] Figure 50 This is a graph showing the EELS analysis results of the positive electrode active material of Example 7.

[0077] Figure 51 This is a graph showing the EELS analysis results of the positive electrode active material of Example 7. Detailed Implementation

[0078] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that one embodiment of the present invention is not limited to the following description, and those skilled in the art will readily understand that the manner and details of the present invention can be varied in various forms. Furthermore, the present invention should not be construed as being limited solely to the content described in the following embodiments.

[0079] Furthermore, in the various figures used in this specification, the size or thickness of each component, such as the positive electrode, negative electrode, active material layer, separator, and outer packaging, is sometimes exaggerated for clarity. Therefore, the dimensions of each component are not limited to the dimensions shown in the figures and the relative dimensions between the components.

[0080] Furthermore, in the structure of the present invention described in this specification and other documents, the same reference numerals are used in different drawings to denote the same part or parts having the same function, thus omitting repeated descriptions. Additionally, sometimes the same shading line is used for parts having the same function without specifically adding reference numerals.

[0081] In this specification, Miller indices are used to describe crystal planes and orientations. In crystallography, numbers using Miller indices are preceded by a superscript; however, in this specification, due to limitations in the description, a negative sign (-) is added before the numbers to indicate crystal planes and orientations. Furthermore, "[]" indicates the individual orientation within a crystal, "<>" indicates the collective orientation of all equivalent crystal directions, "()" indicates the individual direction of a crystal plane, and "{}" indicates a collective plane with equivalent symmetry.

[0082] In this specification, segregation refers to the phenomenon in which a certain element (e.g., B) is not uniformly distributed in a solid formed of multiple elements (e.g., A, B, C).

[0083] In this specification, the layered rock-salt type crystal structure of composite oxides containing lithium and transition metals refers to a crystal structure with an alternating arrangement of cations and anions in a rock-salt type ionic arrangement, where the transition metals and lithium are arranged regularly to form a two-dimensional plane, thus allowing lithium to diffuse in two dimensions. Additionally, defects such as vacancies of cations or anions may also be present. Strictly speaking, in layered rock-salt type crystal structures, there is sometimes lattice deformation of the rock-salt crystals.

[0084] Rock salt-type crystal structures refer to structures in which cations and anions are arranged alternately. In addition, vacancies for either cations or anions may also exist.

[0085] Anions in layered rock salt crystals and rock salt crystals 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 aligned with the cubic closest-packed structure formed by the anions. Note that the space group of layered rock salt crystals is R-3m, which is different from the space group of rock salt crystals, Fm-3m. Therefore, the indices of the crystal faces satisfying the above conditions in layered rock salt crystals are different from those in rock salt crystals. In this specification, the alignment of the cubic closest-packed structure formed by the anions in layered rock salt crystals and rock salt crystals can refer to a state where the crystal orientations are approximately aligned.

[0086] For example, when lithium cobalt oxide with a layered rock salt-type crystal structure comes into contact with magnesium oxide with a rock salt-type crystal structure, the crystal orientations are roughly the same in the following cases: the (1-1-4) face of lithium cobalt oxide is in contact with the {001} face of magnesium oxide; the (104) face of lithium cobalt oxide is in contact with the {001} face of magnesium oxide; the (0-14) face of lithium cobalt oxide is in contact with the {001} face of magnesium oxide; the (001) face of lithium cobalt oxide is in contact with the {111} face of magnesium oxide; the (012) face of lithium cobalt oxide is in contact with the {111} face of magnesium oxide; etc.

[0087] The approximate alignment of crystal orientations in two regions can be determined using 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. X-ray diffraction, electron diffraction, and neutron diffraction can also be used as criteria. In TEM images, the arrangement of cations and anions is observed as repetitions of bright and dark lines. When the orientations of layered rock salt crystals and the cubic close-packed structure of rock salt crystals are aligned, the angle between the repetitions of bright and dark lines in the layered rock salt crystals and those in the rock salt crystals is less than 5 degrees, preferably less than 2.5 degrees. Note that sometimes light elements such as oxygen or fluorine cannot be clearly observed in TEM images; however, in such cases, the alignment of orientations can be determined based on the arrangement of metallic elements.

[0088] Furthermore, in this specification, the state in which two-dimensional interfaces have similar structures is called "epitaxy." Crystallization growth with similar two-dimensional interface structures is called "epitaxy growth." Moreover, the state in which three-dimensional structures have similarities or identical crystallographic orientations is called "topotaxy." Therefore, in the case of topotaxy, when observing a portion of a cross-section, the crystallographic orientations of the two regions (e.g., the substrate region and the region formed through growth) are approximately aligned.

[0089] (Implementation Method 1)

[0090] [Structure of the positive electrode active material]

[0091] First, refer to Figures 1A to 1C This describes a positive electrode active material 100 according to one embodiment of the present invention. For example... Figure 1A As shown, the positive electrode active material 100 includes a first region 101 and a second region 102. The second region 102 may be located on the first region 101 or may cover at least a portion of the first region 101.

[0092] The first region 101 has a different composition than the second region 102. The second region 102 is preferably a region where specific elemental segregation is observed. Therefore, the boundary between these two regions is sometimes indistinct. Figure 1A In the diagram, dashed lines represent the boundary between the first region 101 and the second region 102, and the shades of gray crossing the dashed lines signify the concentration gradient. Figure 1B In the accompanying drawings, for convenience, only dashed lines are used to represent the boundary between the first region 101 and the second region 102. The first region 101 and the second region 102 will be explained in detail later.

[0093] like Figure 1B As shown, the second region 102 can exist within the positive electrode active material. For example, when the first region 101 is polycrystalline, segregation of a specific element can be observed at or near the grain boundaries, thus forming the second region 102. Alternatively, segregation of a specific element can also be observed at or near the portion of the positive electrode active material with crystallization defects, thus forming the second region 102. Note that in this specification, crystallization defects refer to defects that can be observed in TEM images, i.e., structures in which other elements have entered the crystal structure.

[0094] like Figure 1B As shown, the second region 102 does not necessarily need to cover the entire first region 101.

[0095] In other words, the first region 101 exists inside the positive electrode active material 100, and the second region 102 exists on the surface of the positive electrode active material 100. Furthermore, the second region 102 may also exist inside the positive electrode active material 100.

[0096] For example, the first region 101 and the second region 102 can be referred to as solid phase A and solid phase B, respectively.

[0097] When the particle size of the positive electrode active material 100 is too large, the following problems arise: lithium diffusion becomes difficult; the surface of the active material layer is too rough when coated onto the current collector, etc. On the other hand, when the particle size of the positive electrode active material 100 is too small, the following problems arise: the active material layer is not easily supported when coated onto the current collector; excessive reaction with the electrolyte, etc. Therefore, D50 (also known as median particle size) is preferably 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 40 μm or less.

[0098] <Region 1, 101>

[0099] The first region 101 contains lithium, a transition metal, and oxygen. In other words, the first region 101 contains a composite oxide containing lithium and a transition metal.

[0100] As the transition metal included in the first region 101, it is preferable to use a metal that can form a layered rock salt-type composite oxide together with lithium. For example, one or more of manganese, cobalt, and nickel can be used. That is, as the transition metal included in the first region 101, only cobalt can be used, cobalt and manganese can be used, or cobalt, manganese, and nickel can be used. In addition to transition metals, the first region 101 may also include metals other than transition metals such as aluminum.

[0101] That is to say, the first region 101 may include lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which a portion of the cobalt is replaced by manganese, lithium nickel-manganese-cobalt oxide, lithium nickel-cobalt-aluminate, and other composite oxides of lithium and transition metals.

[0102] The first region 101 is used 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 region 102.

[0103] Because lithium readily diffuses in a layered rock-salt crystalline structure, this structure is preferred for the first region 101. Furthermore, unexpectedly, when the first region 101 has a layered rock-salt crystalline structure, segregation of typical elements such as magnesium (described later) tends to occur. Note that the first region 101 as a whole does not necessarily have to have a layered rock-salt crystalline structure. For example, a portion of the first region 101 may have crystal defects, may be amorphous, or may have other crystalline structures.

[0104] <Second Zone 102>

[0105] The second region 102 contains magnesium, fluorine, and oxygen. For example, the second region 102 may contain magnesium oxide, and some of the oxygen may be replaced by fluorine.

[0106] The second region 102 covers at least a portion of the first region 101. The magnesium oxide contained in the second region 102 is an electrochemically stable material that is not easily degraded even with repeated charge and discharge, so the second region 102 is suitable as a capping layer.

[0107] When the thickness of the second region 102 is too thin, its function as a cover layer is reduced; however, when the thickness of the second region 102 is too thick, its capacity decreases. Therefore, the thickness of the second region 102 is preferably 0.5 nm or more and 50 nm or less, more preferably 0.5 nm or more and 3 nm or less.

[0108] The second region 102 preferably has a rock salt-type crystalline structure because its crystal orientation is easily consistent with that of the first region 101, thus the second region 102 can easily be used as a stable overburden layer. Note that the second region 102 as a whole does not necessarily need to have a rock salt-type crystalline structure. For example, a portion of the second region 102 can be amorphous or have other crystalline structures.

[0109] Generally, when repeatedly charged and discharged, side reactions occur in the positive electrode active material, such as the dissolution of transition metals like manganese or cobalt into the electrolyte, oxygen loss, and instability of the crystal structure, thereby deteriorating the positive electrode active material. However, in one embodiment of the present invention, the positive electrode active material 100 includes a second region 102 in the surface layer, which can make the crystal structure of the lithium and transition metal composite oxide in the first region 101 more stable.

[0110] The second region 102 contains magnesium, fluorine, and oxygen, and preferably also contains the same transition metal as the first region 101. When the first region 101 and the second region 102 contain the same transition metal, the valence of the transition metal is preferably different between the two regions. Specifically, it is preferred that in the transition metal contained in the first region 101, there are more trivalent atoms than atoms exhibiting other valences, and in the transition metal contained in the second region 102, there are more divalent atoms than atoms exhibiting other valences.

[0111] When there is a high proportion of divalent transition metals in the second region 102, such as CoO(II), MnO(II), and Ni(II), there are many metal oxides with an atomic ratio of transition metal:oxygen = 1:1. These metal oxides can form stable solid solutions with magnesium oxide, which is also a divalent transition metal. Therefore, the second region 102 can serve as a further stable and excellent capping layer.

[0112] The valence of transition metals can be measured using methods such as electron energy loss spectroscopy (EELS), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and Mössbauer spectroscopy. In particular, EELS is preferred due to its high spatial resolution. Measurements can be performed even when the thickness of the second region 102 is very thin (around a few nm).

[0113] When measuring the valence of transition metals using EELS, the valence can be determined based on the ratio of L3 to L2 (L3 / L2). The larger the L3 / L2 ratio, the higher the proportion of divalent transition metals. For example, when measuring the transition metals contained in the first region 101 and the second region 102 using EELS, the L3 / L2 ratios of the transition metals contained in the first region 101 and the second region 102 are preferably less than 3.8 and greater than 3.8, respectively.

[0114] In addition to the elements mentioned above, the second region 102 may also contain lithium.

[0115] like Figure 1B As shown, it is preferable that a second region 102 also exists in the first region 101, which can further stabilize the crystal structure of the composite oxide containing lithium and transition metal contained in the first region 101.

[0116] Furthermore, the fluorine contained in the second region 102 is preferably present in a bonding state other than MgF2 and LiF. Specifically, when performing XPS analysis on the surface of the positive electrode active material 100, the peak position of the bond energy between fluorine and other elements is preferably above 682 eV and below 685 eV, more preferably around 684.3 eV. This bond energy is not consistent with the bond energy of MgF2 and LiF.

[0117] In this specification, the peak position of the bond energy of an element in XPS analysis refers to the bond energy value at which the maximum value of the energy spectrum intensity is obtained within the range corresponding to the bond energy of that element.

[0118] <Boundary between Region 101 and Region 102>

[0119] 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 and the second region 102 can be confirmed. For example, in cross-sectional TEM and STEM images of the positive electrode active material 100, differences in constituent elements are observed as differences in brightness, thus revealing the differences in the constituent elements of the first region 101 and the second region 102. Furthermore, it can be observed from EDX elemental distribution images that the first region 101 and the second region 102 contain distinct elements. However, it is not necessarily required to observe a clear boundary between the first region 101 and the second region 102 in various analyses.

[0120] In this specification, the range of the second region 102 present on the surface of the positive electrode active material 100 refers to the region from the outermost surface of the positive electrode active material 100 to one-fifth of the peak value of the concentration of typical elements such as magnesium detected in depth direction analysis. For depth direction analysis, linear analysis using EDX or depth direction analysis using ToF-SIMS, as described above, can be used. The magnesium concentration peak is preferably located at a depth of 2 nm from the surface of the positive electrode active material 100 towards the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm. The depth at which the magnesium concentration reaches one-fifth of the peak value, i.e., the range of the second region 102, varies depending on the manufacturing method. However, in the case of the manufacturing method described later, this depth is approximately 2 nm to 5 nm from the surface of the positive electrode active material.

[0121] Similarly, in the second region 102 present in the first region 101, the range of the second region 102 refers to the region where the concentration of magnesium detected by depth direction analysis is more than 1 / 5 of the peak value.

[0122] The fluorine distribution in the positive electrode active material 100 preferably overlaps with the magnesium distribution. Therefore, the fluorine concentration peak preferably exists in a region with a depth of 2 nm from the surface of the positive electrode active material 100 toward the center, more preferably with a depth of 1 nm, and even more preferably with a depth of 0.5 nm.

[0123] Therefore, the second region 102 can refer to the region where the concentrations of magnesium and fluorine gradually decrease from the surface of the positive electrode active material 100 to the interior.

[0124] The concentrations of magnesium and fluorine can be analyzed using methods such as ToF-SIMS, XPS, Auger electron spectroscopy, and TDS.

[0125] XPS measurement range extends from the surface of the positive electrode active material 100 to a depth of approximately 5 nm. Therefore, the elemental concentration at a depth of approximately 5 nm from the surface can be quantitatively analyzed. Thus, when the thickness of the second region 102 is less than 5 nm, the elemental concentration in the region where the second region 102 and a portion of the first region 101 are mixed can be quantitatively analyzed. When the thickness of the second region 102 is 5 nm or more from the surface, the elemental concentration in the second region 102 can be quantitatively analyzed. When performing XPS analysis on the surface of the positive electrode active material 100, when the total amount of atoms containing lithium, the transition metal contained in the first region 101, oxygen, fluorine, and magnesium is 100 atomic%, the magnesium concentration is preferably 1 atomic% or more and 16 atomic% or less, and the fluorine concentration is preferably 0.2 atomic% or more and 4 atomic% or less. Furthermore, the magnesium to fluorine concentration ratio is preferably Mg:F = y:1 (3 ≤ y ≤ 5) (atomic ratio), more preferably Mg:F = approximately 4:1. When the magnesium and fluorine concentrations are within the above ranges, a positive electrode active material 100 can be achieved that exhibits extremely high cycle characteristics when used in secondary batteries.

[0126] As described above, the concentrations of magnesium and fluorine gradually decrease from the surface inwards; therefore, the first region 101 may also contain elements such as magnesium contained in the second region 102. Similarly, the second region 102 may also contain elements contained in the first region 101. Furthermore, the first region 101 may also contain other elements such as carbon, sulfur, silicon, sodium, calcium, chlorine, and zirconium. The second region 102 may also contain other elements such as carbon, sulfur, silicon, sodium, calcium, chlorine, and zirconium.

[0127] [Analysis]

[0128] The second region 102 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 a magnesium source and a fluorine source are mixed with a starting material and the mixture is then heated, magnesium segregates, forming the second region 102. Furthermore, the inventors have also discovered that the positive electrode active material including the second region 102 formed by the above method has further improved properties.

[0129] For example, in Example 4 of Patent Document 2 (Japanese Patent Application Publication No. 2016-076454), a composite oxide containing magnesium was synthesized, and then the powder of the composite oxide was mixed with lithium fluoride and heated to form a fluorinated and lithiumized surface oxide on the surface of the composite oxide. According to Example 4, magnesium was not detected in the surface oxide formed by the above method.

[0130] However, the inventors achieved magnesium oxide segregation on the surface of the positive electrode active material 100 by mixing a magnesium source and a fluorine source with the starting material. The inventors discovered that the fluorine added to the starting material exhibited an unexpected effect in causing magnesium segregation.

[0131] Since the second region 102 is formed by magnesium segregation, magnesium segregation can occur not only on the surface of the positive electrode active material 100 but also at and near grain boundaries and crystal defects. The formation of the second region 102 at and near grain boundaries and crystal defects can contribute to the stabilization of the crystal structure of the composite oxide containing lithium and transition metals included in the first region 101.

[0132] In order to efficiently generate segregation in the second region 102, the concentration ratio of magnesium to fluorine in the starting material is preferably in the range of Mg:F = 1:x (1.5 ≤ x ≤ 4) (atomic ratio), and more preferably around Mg:F = 1:2 (atomic ratio).

[0133] The concentration ratio of magnesium and fluorine contained in the second region 102 formed by segregation is preferably in the range of Mg:F = y:1 (3≤y≤5) (atomic number ratio), for example, more preferably Mg:F = about 4:1.

[0134] The second region 102, formed by segregation, is formed by epitaxial growth, so the crystal orientations of the first region 101 and the second region 102 are sometimes partially and approximately aligned. That is, the first region 101 and the second region 102 are sometimes topologically derived. When the crystal orientations of the first region 101 and the second region 102 are approximately aligned, the second region 102 can be used as a better capping layer.

[0135] <Third District 103>

[0136] Note that although the above description illustrates examples of the positive electrode active material 100 including the first region 101 and the second region 102, one embodiment of the present invention is not limited thereto. For example, as Figure 1C As shown, the positive electrode active material 100 may also include a third region 103. The third region 103 may be configured to contact at least a portion of the second region 102. The third region 103 may be a capping film containing carbon, such as graphene compounds, or a capping film containing lithium or electrolyte decomposition products. When the third region 103 is a carbon-containing capping film, the conductivity between the positive electrode active materials 100 and between the positive electrode active material 100 and the current collector can be improved. When the third region 103 is a capping film containing lithium or electrolyte decomposition products, excessive reaction with the electrolyte can be suppressed and the cycle characteristics when used in a secondary battery can be improved.

[0137] Alternatively, a buffer region may be provided between the first region 101 and the second region 102. The buffer region preferably includes metals such as titanium, aluminum, zirconium, and vanadium, in addition to lithium, transition metals, and oxygen. The buffer region may also overlap with the first region 101 and the second region 102. When a positive electrode active material 100 including the buffer region is used, the crystal structure of the first region 101 and the second region 102 can be further stabilized, thereby achieving a positive electrode active material with extremely high cycle characteristics, which is therefore preferred.

[0138] [Manufacturing Method]

[0139] Reference Figure 2 This invention describes a method for manufacturing a positive electrode active material 100, including a first region 101 and a second region 102. In this method, the second region 102 is formed by segregation. In this embodiment, the transition metal contained in the first region 101 is cobalt, that is, the first region 101 contains lithium cobalt oxide. Furthermore, the second region 102, containing magnesium oxide and fluorine, is formed by segregation.

[0140] First, prepare the starting materials (S11). Specifically, weigh the lithium source, cobalt source, magnesium source, and fluorine source. For example, lithium carbonate, lithium fluoride, and lithium hydroxide can be used as the lithium source. For example, cobalt oxide, cobalt hydroxide, cobalt hydroxide oxide, cobalt carbonate, cobalt oxalate, and cobalt sulfate can be used as the cobalt source. For example, magnesium oxide and magnesium fluoride can be used as the magnesium source. For example, lithium fluoride and magnesium fluoride can be used as the fluorine source. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can be used as either a magnesium source or a fluorine source.

[0141] In this embodiment, lithium carbonate (Li2CO3) is used as the lithium source, cobalt oxide (Co3O4) is used as the cobalt source, magnesium oxide (MgO) is used as the magnesium source, and lithium fluoride (LiF) is used as both the lithium source and the fluorine source.

[0142] The preferred atomic ratio of magnesium to fluorine in the raw materials is Mg:F = 1:x (1.5 ≤ x ≤ 4), more preferably Mg:F = 1:2. Therefore, the preferred molar ratio of magnesium oxide to lithium fluoride is MgO:LiF = 1:x (1.5 ≤ x ≤ 4), more preferably MgO:LiF = 1:2.

[0143] For example, the molar ratio of each material can be as follows:

[0144] 1 / 2·Li2CO3+((1-z) / 3)·Co3O4+z·MgO+2z·LiF

[0145] (z = 0.01)

[0146] Next, the weighed starting materials are mixed (S12). For example, a ball mill, sand mill, etc. can be used for mixing.

[0147] Next, the material mixed in S12 is heated (S13). To distinguish it from subsequent heating steps, this step can be referred to as the first heating or calcination. The first heating is preferably performed at 800°C or higher and 1050°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. The first heating is preferably performed in a dry atmosphere, such as dry air. In a dry atmosphere, for example, the dew point is preferably -50°C or lower, more preferably -100°C or lower. In this embodiment, heating is performed 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.

[0148] By first heating in S13, the composite oxide containing lithium and transition metals included in the first region 101 can be synthesized. Furthermore, by this first heating, a portion of the magnesium and fluorine contained in the starting material segregates to the surface of the composite oxide containing lithium and transition metals. Note that at this time, most of the magnesium and fluorine form a solid solution in the composite oxide containing lithium and transition metals.

[0149] Next, the material heated in S13 is cooled to room temperature (S14). This cooling time is preferably equal to or longer than the heating time, for example, 10 hours or more but less than 15 hours. After cooling, the synthesized material is preferably screened. In this embodiment, a 53 μm wire mesh sieve is used.

[0150] Alternatively, pre-synthesized composite oxide particles containing lithium, cobalt, fluorine, and magnesium can be used as starting materials. In this case, steps S12 to S14 can be omitted.

[0151] Next, the material cooled in S14 is subjected to a second heating (S15). To distinguish this from the previous heating process, this process can be referred to as a second heating or annealing. The optimal conditions for the second heating vary depending on the particle size and composition of the composite oxide containing lithium, cobalt, fluorine, and magnesium. However, the holding time at the specified temperature is preferably 50 hours or less, more preferably 2 hours or more and 10 hours or less. The specified temperature is preferably 500°C or more and 1200°C or less, more preferably 700°C or more and 1000°C or less, and even more preferably around 800°C. Heating is preferably performed in an oxygen-containing atmosphere. In this embodiment, heating is performed under the following conditions: 800°C; 2 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.

[0152] The second heating in S15 can promote the segregation of magnesium and fluorine contained in the starting material in the surface layer of the composite oxide containing lithium and transition metals.

[0153] Finally, the material heated in S15 is cooled to room temperature. This cooling time is preferably equal to or longer than the heating time. Then, the cooled material is recovered (S16), thereby obtaining a positive electrode active material 100 comprising a first region 101 and a second region 102.

[0154] By using the positive electrode active material described in this embodiment, a secondary battery with high capacity and excellent cycle characteristics can be provided. This embodiment can be implemented in appropriate combination with other embodiments.

[0155] (Implementation Method 2)

[0156] 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.

[0157] [positive electrode]

[0158] The positive electrode includes the positive electrode active material layer and the positive electrode current collector.

[0159] <Positive Electrode Active Material Layer>

[0160] The positive electrode active material layer contains the positive electrode active material. The positive electrode active material layer may also contain conductive additives and binders.

[0161] The positive electrode active material 100 described in the above embodiments can be used as the positive electrode active material. When the above positive electrode active material 100 is used, a secondary battery with high capacity and excellent cycle characteristics can be realized.

[0162] Examples of conductive additives include carbon materials, metallic materials, and conductive ceramic materials. Furthermore, fibrous materials can also be used as conductive additives. 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.

[0163] By utilizing conductive additives, a conductive network can be formed in the electrode. Conductive additives also maintain the conductive paths between the positive electrode active material particles. Adding conductive additives to the active material layer can improve its conductivity.

[0164] Examples of conductive additives include natural graphite, artificial graphite such as mesophase carbon microspheres, and carbon fibers. Examples of carbon fibers include mesophase pitch-based carbon fibers, isotropic pitch-based carbon fibers, carbon nanofibers, and carbon nanotubes. For example, carbon nanotubes can be manufactured using vapor-phase growth. Other examples of conductive additives include carbon black (e.g., acetylene black (AB)), graphite (lead black) particles, graphene, fullerenes, and other carbon materials. Furthermore, metal powders or fibers of copper, nickel, aluminum, silver, gold, etc., and conductive ceramic materials can also be used.

[0165] In addition, graphene compounds can also be used as conductive additives.

[0166] Graphene compounds possess excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Furthermore, graphene compounds have a planar shape. Graphene compounds can achieve surface contacts with low contact resistance. Moreover, 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, graphene compounds are preferably used as conductive additives because they can increase the contact area between the active material and the conductive additive. Particularly preferred are graphene, multilayer graphene, or reduced graphene oxide (hereinafter, "RGO") used as the graphene compound. Here, RGO refers, for example, to a compound obtained by reducing graphene oxide (GO).

[0167] When using active materials with small particle sizes (e.g., less than 1 μm), the specific surface area of ​​the active material is large, thus requiring more conductive paths between the active materials. Therefore, there is a tendency for the amount of conductive additive to increase, while the content of the active material tends to decrease relatively. When the content of the active material decreases, the capacity of the secondary battery also decreases. In this case, since the content of the active material is not reduced, it is particularly preferable to use graphene compounds, which can efficiently form conductive paths even in small amounts, as conductive additives.

[0168] The following describes an example of the cross-sectional structure of the active material layer 200, which contains a graphene compound as a conductive additive.

[0169] Figure 3A A longitudinal cross-sectional view of the active material layer 200 is shown. The active material layer 200 includes positive electrode active material particles 100, a 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. The graphene compound 201 preferably has a sheet-like shape. The graphene compound 201 may have a sheet-like shape formed by partially overlapping multiple multilayer graphenes and / or multiple graphenes.

[0170] exist Figure 3A In the longitudinal section of the active material layer 200, sheet-like graphene compounds 201 are generally uniformly dispersed within the active material layer 200. Figure 3A Graphene compound 201 is schematically represented by a thick line, but in reality, graphene compound 201 is a thin film with a thickness corresponding to the thickness of a single layer or multiple layers of carbon molecules. Multiple graphene compounds 201 are formed in such a way that they partially cover or adhere to the surface of multiple positive electrode active material particles 100, thereby forming surface contact between the graphene compounds 201 and the positive electrode active material particles 100.

[0171] Here, multiple graphene compounds are bonded together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound mesh or graphene network). The graphene network covering the active material can be used as a binder to bind the active material together. Therefore, the amount of binder can be reduced or eliminated. As a result, the proportion of active material in the electrode volume or electrode weight can be increased. That is, the capacity of the energy storage device can be increased.

[0172] 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. When highly dispersible graphene oxide in a polar solvent is used in the formation of the graphene compound 201, the graphene compound 201 can be dispersed substantially uniformly in the active material layer 200. By evaporating and removing the solvent from the dispersion medium in which the graphene oxide is uniformly dispersed, and reducing the graphene oxide, 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 be carried out, for example, by heat treatment or by using a reducing agent.

[0173] 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. Therefore, the conductivity between the positive electrode active material particles 100 and graphene compound 201 can be improved with less graphene compound 201 than with general conductive additives. Consequently, the proportion of positive electrode active material 100 in the active material layer 200 can be increased, thereby increasing the discharge capacity of the energy storage device.

[0174] As adhesives, rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer can be used. In addition, fluororubber can also be used as an adhesive.

[0175] As an adhesive, a water-soluble polymer is preferred, for example. Polysaccharides can be used as water-soluble polymers. Among the 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.

[0176] Alternatively, as an adhesive, materials such as polystyrene, polymethyl acrylate, 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.

[0177] As an adhesive, multiple of the above materials can also be used in combination.

[0178] For example, materials with particularly high viscosity-modifying properties can be used in combination with other materials. For instance, rubber materials have high adhesive strength and high elasticity, but viscosity can sometimes be difficult to adjust when mixed in a solvent. In such cases, it is preferable to mix rubber materials with materials that have particularly high viscosity-modifying properties. Water-soluble polymers are preferred as materials with particularly high viscosity-modifying properties. Examples of water-soluble polymers with particularly good viscosity-modifying properties include the aforementioned polysaccharides, such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, and starch.

[0179] Furthermore, cellulose derivatives such as carboxymethyl cellulose exhibit increased solubility when converted into sodium or ammonium salts of carboxymethyl cellulose, thus readily functioning as viscosity modifiers. This increased solubility enhances the dispersibility of the active material with other components in the electrode slurry. In this specification, cellulose and cellulose derivatives used as electrode binders comprise their salts.

[0180] Water-soluble polymers stabilize their viscosity by dissolving in water, allowing active materials and other materials used as binders, such as styrene-butadiene rubber, to be stably dispersed in aqueous solutions. Furthermore, 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, mostly possess functional groups such as hydroxyl and carboxyl groups. Because of these functional groups, polymers are expected to interact and extensively cover the surface of active materials.

[0181] When an adhesive forms a film covering or contacting the surface of an active material, this film is expected to function as a passivation film to suppress electrolyte decomposition. Here, a passivation film refers to a film that has no conductivity or very low conductivity; for example, when a passivation film is formed on the surface of the active material, electrolyte decomposition can be suppressed at the potential for battery reaction. Preferably, the passivation film is capable of transporting lithium ions while suppressing conductivity.

[0182] Positive current collector

[0183] The positive electrode current collector can be formed from highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, or their alloys. Preferably, the material used for the positive electrode current collector does not dissolve due to the potential of the positive electrode. Furthermore, the positive electrode current collector can be formed from aluminum alloys with added elements to improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum. Additionally, metallic elements that react with silicon to form silicides can be used. Examples of metallic 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 have various shapes, such as foil, plate (sheet), mesh, perforated metal mesh, or drawn metal mesh. The thickness of the current collector is preferably from 5 μm to 30 μm.

[0184] [negative electrode]

[0185] 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.

[0186] <Negative Electrode Active Material>

[0187] As the negative electrode active material, alloy materials or carbon materials can be used, for example.

[0188] As the negative electrode active material, elements capable of charge-discharge reactions through alloying and dealloying reactions 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. In particular, silicon has a high theoretical capacity of 4200 mAh / g. Therefore, silicon is preferred for use as the negative electrode active material. Alternatively, compounds containing these elements can also be used. Examples of such compounds include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions through alloying and dealloying reactions with lithium, as well as compounds containing such elements, are sometimes referred to as alloy materials.

[0189] In this specification and other materials, SiO refers, for example, to silicon monoxide. SiO can 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.

[0190] 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.

[0191] Examples of graphite include synthetic graphite and natural graphite. Examples of synthetic graphite include mesophase carbon microspheres (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Spherical graphite with a spherical shape can be used as synthetic graphite. For example, MCMB is preferred because it sometimes has a spherical shape. Furthermore, MCMB is sometimes preferred because it is easier to reduce its surface area. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0192] 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 have 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 the preferred choice.

[0193] 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), and molybdenum oxide (MoO2).

[0194] Additionally, 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, or Cu). For example, Li 2.6 Co 0.4 N3 exhibits a large charge / discharge capacity (900 mAh / g and 1890 mAh / cm³). 3 Therefore, it is the preferred option.

[0195] Preferably, nitrides containing lithium and transition metals are used, in which case 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, used as positive electrode active materials. When lithium-ion-containing materials are used as positive electrode active materials, lithium nitrides containing lithium and transition metals can be used as negative electrode active materials by pre-deintercalating and deintercalating the lithium ions contained in the positive electrode active material.

[0196] Furthermore, materials that induce the conversion reaction can 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. 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.

[0197] 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.

[0198] <Negative Electrode Current Collector>

[0199] 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.

[0200] Electrolyte

[0201] The electrolyte comprises a solvent and an electrolyte. A non-protic organic solvent is preferably used as the solvent for the electrolyte. For example, one of the following solvents can be used: 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 diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sulfonyl ether, etc., or two or more of the above solvents can be used in any combination and in any ratio.

[0202] When gelled polymer materials are used as solvents for electrolytes, safety against leakage is improved. Furthermore, it allows for the thinning and weight reduction of secondary batteries. Typical examples of gelled polymer materials include silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polyoxypropylene gels, and fluoropolymer gels.

[0203] Furthermore, when one or more flame-retardant and non-volatile ionic liquids (room temperature molten salts) are used as the solvent for the electrolyte, the battery can be prevented from rupturing or catching fire even if a short circuit occurs inside the battery or its internal temperature rises due to overcharging. Ionic liquids contain both cations and anions. Examples of organic cations used in electrolytes include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in electrolytes include monovalent amide anions, monovalent methylide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, and perfluoroalkyl phosphate anions.

[0204] As electrolytes dissolved in the above solvents, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B can be used. 10 Cl 10 Li2B 12 Cl 12One 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 lithium salts can be used in any combination and any ratio.

[0205] The electrolyte used in the energy storage device is preferably a highly purified electrolyte, and the content of elements other than the constituent elements of the electrolyte (hereinafter referred to as impurities) and particulate dust is low. Specifically, the weight ratio of impurities in the electrolyte is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0206] In addition, additives such as vinylene carbonate, propanesulfonate lactone (PS), tert-butylbenzene (TBB), fluoroethylene vinyl carbonate (FEC), LiBOB, or dinitrile compounds such as succinate and adiponitrile can be added to the electrolyte. The concentration of the additive relative to the total solvent is, for example, 0.1 wt% or more and 5 wt% or less.

[0207] Alternatively, a polymer gel electrolyte, obtained by swelling the polymer in an electrolyte solution, can be used. When using a polymer gel electrolyte, safety regarding leakage is improved. Furthermore, it allows for the reduction in the thickness and weight of the secondary battery.

[0208] As a gelling polymer, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polyoxypropylene gels, fluoropolymer gels, etc. can be used.

[0209] Examples of polymers include polyethylene oxide (PEO) and other polymers with polyoxyalkylene structures, PVDF and polyacrylonitrile, and copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The resulting polymer can also have a porous structure.

[0210] Alternatively, solid electrolytes containing inorganic materials such as sulfide-based or oxide-based inorganic materials, or solid electrolytes containing polymeric materials such as polyethylene oxide (PEO), can be used instead of liquid electrolytes. When using solid electrolytes, there is no need to install separators or spacers. Furthermore, since the entire battery can be solidified, there are no concerns about leakage, significantly improving safety.

[0211] [Isolation]

[0212] The secondary battery preferably includes a separator. As the separator, materials such as paper, nonwoven fabric, glass fiber, ceramic, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic resin, polyolefin, or polyurethane can be used. The separator is preferably formed in a bag shape, surrounding either the positive or negative electrode.

[0213] 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 films. Examples of ceramic materials include alumina particles and silicon oxide 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).

[0214] Coating the separator with ceramic materials improves its oxidation resistance, thereby suppressing separator degradation during high-voltage charging and discharging and enhancing the reliability of the secondary battery. Furthermore, coating the separator with fluorine-based materials facilitates a tighter connection between the separator and the electrodes, improving output characteristics. Coating the separator with polyamide-based materials (especially aromatic polyamides) improves heat resistance, thus enhancing the safety of the secondary battery.

[0215] 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.

[0216] 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.

[0217] (Implementation Method 3)

[0218] In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. Regarding the materials used in the secondary battery described in this embodiment, please refer to the description in the above embodiment.

[0219] [Coin-type rechargeable battery]

[0220] First, let's look at an example of a coin-type secondary battery. Figure 4A This is an image of a coin-shaped (single-layer flat) secondary battery. Figure 4B This is its cross-sectional view.

[0221] 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 includes a positive current collector 305 and a positive active material layer 306 disposed in contact with the positive current collector 305. The negative electrode 307 includes a negative current collector 308 and a negative active material layer 309 disposed in contact with the negative current collector 308.

[0222] Each of the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300 has an active material layer on only one surface.

[0223] 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 and the negative electrode container 302 are electrically connected to the positive electrode 304 and the negative electrode 307, respectively.

[0224] The negative electrode 307, positive electrode 304, and separator 310 are immersed in the electrolyte. Then, as... Figure 4B As shown, the positive electrode 304, the separator 310, the negative electrode 307, and the negative electrode can 302 are stacked sequentially below the positive electrode can 301, and the positive electrode can 301 and the negative electrode can 302 are pressed together with a gasket 303. In this way, a coin-shaped secondary battery 300 can be manufactured.

[0225] When the positive electrode active material described in the above embodiments is used in the positive electrode 304, a coin-type secondary battery 300 with high capacity and excellent cycle characteristics can be realized.

[0226] Cylindrical secondary battery

[0227] Next, refer to Figures 5A to 5D An example of a cylindrical secondary battery will be given. For example... Figure 5A 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.

[0228] Figure 5BThis is a cross-sectional schematic 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 and 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, with its positive electrode, negative electrode, and insulator wound around it, is disposed between a pair of opposing insulating plates 608 and 609. Additionally, a non-aqueous electrolyte (not shown) is injected into the battery can 602, in which the battery element is disposed. The same non-aqueous electrolyte used in coin-type secondary batteries can be used as the non-aqueous electrolyte.

[0229] Because the positive and negative electrodes of the cylindrical secondary battery are wound together, the active material is preferably formed on both surfaces of the current collector. The positive terminal (positive current collector wire) 603 is connected to the positive electrode 604, and the negative terminal (negative current collector wire) 607 is connected to the negative electrode 606. Both the positive terminal 603 and the negative terminal 607 can be formed using metal materials such as aluminum. The positive terminal 603 and the negative terminal 607 are respectively resistance-welded to the safety valve mechanism 612 and 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 exceeds a specified threshold, the safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604. The PTC element 611 is used as a heat-sensitive resistor whose resistance increases with temperature, and the increased resistance limits the current to prevent abnormal heating. Barium titanate (BaTiO3) type semiconductor ceramics can be used as the PTC element.

[0230] In addition, such as Figure 5C 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 also be connected in parallel, in series, or in parallel followed by series connection. By using a module 615 including multiple secondary batteries 600, a larger amount of power can be extracted.

[0231] Figure 5D This is a top view of module 615. For clarity, the conductive plate 613 is represented by dashed lines. Figure 5DAs shown, module 615 may include wires 616 that electrically connect multiple secondary batteries 600 to each other. A conductive plate 613 may be disposed on the wires 616 in a manner overlapping the wires 616. Additionally, a temperature control device 617 may be disposed among the multiple secondary batteries 600. When a secondary battery 600 overheats, the temperature control device 617 can cool the secondary battery 600; when a secondary battery 600 is undercooled, the temperature control device 617 can heat the secondary battery 600. Therefore, the performance of module 615 is less susceptible to the influence of external temperature.

[0232] When the positive electrode active material described in the above embodiments is used in the positive electrode 604, a cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be realized.

[0233] [Example of a secondary battery structure]

[0234] Reference Figure 6A and Figure 6B , Figure 7A1 , Figure 7A2 , Figure 7B1 , Figure 7B2 , Figure 8A and Figure 8B as well as Figure 9 Other structural examples of secondary batteries are illustrated.

[0235] Figure 6A and Figure 6B This is an external view of the battery pack. The battery pack includes a circuit board 900 and a secondary battery 913. The secondary battery 913 includes terminals 951 and 952 and is covered by a label 910. The battery pack may also include an antenna 914.

[0236] The circuit board 900 is secured by a sealing material 915. The circuit board 900 includes a circuit 912. Terminals 911 are electrically connected to terminals 951 and 952 of the secondary battery 913 via the circuit board 900. Terminals 911 are also electrically connected to the antenna 914 and the circuit 912 via the circuit board 900. Alternatively, multiple terminals 911 can be provided, which can be used as control signal input terminals, power supply terminals, etc.

[0237] For example, circuit 912 serves as a protection circuit to protect secondary battery 913 from the effects of overcharging, over-discharging, and overcurrent. Circuit 912 can also be disposed on the back of circuit board 900. Furthermore, the shape of antenna 914 is not limited to a coil shape; it can also be linear or plate-shaped. Additionally, planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, or dielectric antennas can be used. Antenna 914, for example, has the function of data communication with external devices. As a communication system using antenna 918 between the battery pack and other devices, a response method such as NFC can be used for communication between the battery pack and other devices.

[0238] The battery pack includes a layer 916 between the secondary battery 913 and the antenna 914. Layer 916, for example, functions to shield against electromagnetic fields from the secondary battery 913. A magnetic material can be used, for example, as layer 916.

[0239] Note that the structure of the battery pack is not limited to... Figure 6A and Figure 6B The structure shown.

[0240] For example, such as Figure 7A1 and Figure 7A2 As shown, Figure 6A and Figure 6B Antennas can also be installed on the two opposing surfaces of the secondary battery 913. Figure 7A1 This is an external view showing one side of one of the aforementioned opposing surfaces. Figure 7A2 This is a view showing the appearance of one side of the other surface in the aforementioned opposing surfaces. Regarding... Figure 6A and Figure 6B The same parts can be appropriately referenced. Figure 6A and Figure 6B Description of the battery pack shown.

[0241] like Figure 7A1 As shown, an antenna 914 is disposed on one of the opposing surfaces of the secondary battery 913, with a layer 916 sandwiched between them. Figure 7A2 As shown, an antenna 918 is disposed on another surface 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. As layer 917, a magnetic material can be used, for example.

[0242] By adopting the above structure, the battery pack can have two antennas, and the size of both antennas 914 and 918 can be increased.

[0243] As antenna 918, an antenna with a shape applicable to antenna 914 can be used. Antenna 918 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 can also be used as one of the two conductors of a capacitor. Thus, not only electromagnetic or magnetic fields can be used, but also electric fields can be used to exchange electricity.

[0244] Or, such as Figure 7B1 As shown, Figure 6A and Figure 6B The battery pack can also be equipped with a display device 920. The display device 920 is electrically connected to terminal 911. Regarding... Figure 6A and Figure 6B The same parts can be appropriately referenced. Figure 6A and Figure 6B Description of the battery pack shown.

[0245] The display device 920 can display images indicating whether charging is in progress, images indicating the amount of power stored, etc. Electronic paper, liquid crystal displays, electroluminescent (EL) displays, etc., can be used as the display device 920. For example, by using electronic paper, the power consumption of the display device 920 can be reduced.

[0246] Or, such as Figure 7B2 As shown, Figure 6A and Figure 6B The secondary battery 913 shown can also be equipped with a sensor 921. The sensor 921 is electrically connected to terminal 911 via terminal 922 and circuit board 900. Regarding... Figure 6A and Figure 6B The same parts can be appropriately referenced. Figure 6A and Figure 6B Description of the energy storage device shown.

[0247] Sensor 921 may 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, data showing the environment in which the energy storage device is set (e.g., temperature) can be detected and stored in the memory of circuit 912.

[0248] Furthermore, refer to Figure 8A and Figure 8B as well as Figure 9 The structure of the secondary battery 913 is illustrated using an example.

[0249] Figure 8A 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 an electrolyte inside the frame 930. Terminal 952 contacts the frame 930. Insulating material or the like prevents terminal 951 from contacting the frame 930. Note that, for convenience, in Figure 8A The diagram shows a separate frame 930; however, in practice, the wound body 950 is 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 (such as aluminum) or resin.

[0250] In addition, such as Figure 8B As shown, multiple materials can also be used to form Figure 8A The frame 930. For example, in Figure 8BIn the secondary battery 913, the frame 930a and the frame 930b are attached together, and the winding body 950 is disposed in the area surrounded by the frame 930a and the frame 930b.

[0251] As the frame 930a, insulating materials such as organic resin can be used. In particular, when materials such as organic resin are used to form the antenna surface, shielding due to the electric field of the secondary battery 913 can be suppressed. When the shielding due to the electric field of the frame 930a is small, antennas such as antennas 914 and 918 can be installed inside the frame 930a. As the frame 930b, for example, a metal material can be used.

[0252] Figure 9 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 obtained 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 including the negative electrode 931, the positive electrode 932, and the insulator 933 can be stacked.

[0253] Negative electrode 931 is connected to one of terminals 951 and 952. Figure 6A and Figure 6B Terminal 911 is connected. Positive terminal 932 is connected to the other of terminals 951 and 952. Figure 6A and Figure 6B Terminal 911 is connected.

[0254] When the positive electrode active material described in the above embodiments is used in the positive electrode 932, a secondary battery 913 with high capacity and excellent cycle characteristics can be realized.

[0255] [Laminated secondary battery]

[0256] Next, refer to Figures 10A to 10C , Figure 11A and Figure 11B , Figure 12 , Figure 13 , Figures 14A to 14C , Figure 15A , Figure 15B1 , Figure 15B2 , Figure 15C and Figure 15D as well as Figure 16A and Figure 16B An example of a laminated secondary battery is given. When a laminated secondary battery is flexible and is used in an electronic device that is at least partially flexible, the secondary battery can be bent along the deformation of the electronic device.

[0257] Reference Figures 10A to 10C Description of laminated secondary battery 980. Laminated secondary battery 980 includes... Figure 10AThe wound body 993 is shown. The wound body 993 includes a negative electrode 994, a positive electrode 995, and an insulator 996. (And...) Figure 9 Similarly, the winding body 950 described herein is obtained 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.

[0258] Furthermore, the number of layers in the stack, including the negative electrode 994, the positive electrode 995, and the insulator 996, can be appropriately determined according to the required capacity and component volume. The negative electrode 994 is connected to the negative current collector (not shown) via one of the wire electrodes 997 and 998. The positive electrode 995 is connected to the positive current collector (not shown) via the other of the wire electrodes 997 and 998.

[0259] like Figure 10B As shown, the wound body 993 is accommodated in the space formed by bonding the film 981, which is used as the outer packaging body, and the film 982 having a recess by means of heat pressing, thereby forming a Figure 10C The secondary battery 980 is shown. The wound body 993 includes wire electrodes 997 and 998, and is immersed in electrolyte within the space formed by the thin film 981 and the thin film 982 having a recess.

[0260] For example, a metallic material such as aluminum or a resin material can be used as the thin film 981 and the thin film 982 with the recess. By using a resin material as the thin film 981 and the thin film 982 with the recess, the thin film 981 and the thin film 982 with the recess can be deformed when an external force is applied, thereby enabling the manufacture of a flexible secondary battery.

[0261] Although Figure 10B and Figure 10C An example is shown where two membranes form a space, but the aforementioned wound body 993 can also be configured to bend a single membrane to form a space.

[0262] When the positive electrode active material described in the above embodiments is used in the positive electrode 995, a secondary battery 980 with high capacity and excellent cycle characteristics can be achieved.

[0263] exist Figures 10A to 10C The image shows an example of a secondary battery 980 that includes a wound body within the space formed by a film used as an outer packaging body, but as... Figure 11A and Figure 11B As shown, a secondary battery can also include multiple rectangular positive electrodes, multiple rectangular separators, and multiple rectangular negative electrodes in the space formed by the film used as the outer packaging.

[0264] Figure 11AThe laminated secondary 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. The outer packaging 509 is filled with the electrolyte 508. The electrolyte 508 shown in Embodiment 2 can be used as the electrolyte 508.

[0265] exist Figure 11A In the laminated secondary battery 500 shown, the positive current collector 501 and the negative current collector 504 are also used as terminals for electrical contact with the outside. Therefore, the positive current collector 501 and the negative current collector 504 can also be configured to partially expose the outside of the outer casing 509. Alternatively, the wire electrode can be ultrasonically welded to the positive current collector 501 or the negative current collector 504, thereby exposing 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.

[0266] As the outer packaging 509 of the laminated secondary battery 500, a laminated film with a three-layer structure can be used, for example: 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.

[0267] Figure 11B An example of the cross-sectional structure of a laminated secondary battery 500 is shown. For simplicity, Figure 11A The example shown includes two current collectors, but a real battery includes multiple electrode layers.

[0268] Figure 11B The example in the example includes 16 electrode layers. Even with 16 electrode layers, the secondary battery 500 is flexible. Figure 11B The diagram shows a structure comprising a total of 16 layers, including 8 layers of negative electrode current collector 504 and 8 layers of positive electrode current collector 501. Additionally, Figure 11B The cross-section of the negative electrode extraction section is shown, with eight layers of negative electrode current collector 504 joined together by ultrasonic welding. 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, the secondary battery can have a larger capacity. Conversely, with a smaller number of electrode layers, the secondary battery can have a thinner profile and better flexibility.

[0269] Figure 12 and Figure 13An example of the appearance of a laminated secondary battery 500 is shown. Figure 12 and Figure 13 It includes: positive electrode 503; negative electrode 506; separator 507; outer packaging 509; positive electrode lead 510; and negative electrode lead 511.

[0270] Figure 14A 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. The positive electrode 503 also has a portion of the positive current collector 501 exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative current collector 504, and a negative active material layer 505 is formed on the surface of the negative current collector 504. The negative electrode 506 also has a portion of the negative current collector 504 exposed, i.e., the tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited. Figure 14A The example shown.

[0271] [Manufacturing method of laminated secondary batteries]

[0272] Here, refer to Figure 14B and Figure 14C For Figure 12 An example of a method for manufacturing a laminated secondary battery, showing its appearance, will be explained.

[0273] First, the negative electrode 506, the insulator 507, and the positive electrode 503 are stacked. Figure 14B The diagram shows a stack comprising a negative electrode 506, an insulator 507, and a positive electrode 503. An example with 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. This joining can be performed, for example, using ultrasonic welding. 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.

[0274] Then, a negative electrode 506, an isolator 507, and a positive electrode 503 are configured on the outer packaging body 509.

[0275] Next, as Figure 14C As shown, the outer packaging body 509 is folded along the dotted line. Then, the outer periphery of the outer packaging body 509 is joined. This joining can be done, for example, by heat pressing. At this time, in order to inject the electrolyte 508 later, a portion (or an edge) of the outer packaging body 509 is left unjointed (to provide an inlet).

[0276] Next, electrolyte 508 is introduced into the outer packaging 509 through the inlet. Preferably, electrolyte 508 is introduced under reduced pressure or an inert gas atmosphere. Finally, the inlet is closed. A laminated secondary battery 500 can be manufactured in this manner.

[0277] When the positive electrode active material described in the above embodiments is used in the positive electrode 503, a secondary battery 500 with high capacity and excellent cycle characteristics can be achieved.

[0278] [Flexible rechargeable battery]

[0279] Next, refer to Figure 15A , Figure 15B1 , Figure 15B2 , Figure 15C and Figure 15D as well as Figure 16A and Figure 16B An example of a flexible secondary battery will be given.

[0280] Figure 15A A top view schematic diagram of the flexible secondary battery 250 is shown. Figure 15B1 , Figure 15B2 , Figure 15C They are along Figure 15A The diagram shows cross-sectional views of cut lines C1-C2, C3-C4, and A1-A2. Battery 250 includes an outer casing 251, and a positive electrode 211a and a negative electrode 211b housed within the outer casing 251. A wire 212a electrically connected to the positive electrode 211a and a wire 212b electrically connected to the negative electrode 211b extend to the outside of the outer casing 251. An electrolyte (not shown) is sealed within the area surrounded by the outer casing 251, in addition to the positive electrode 211a and the negative electrode 211b.

[0281] Figure 16A and Figure 16B The positive electrode 211a and negative electrode 211b of the battery 250 are shown. Figure 16A It is a three-dimensional diagram illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the insulator 214. Figure 16B It is a three-dimensional diagram showing wires 212a and 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0282] like Figure 16A As shown, the battery 250 includes multiple rectangular positive electrodes 211a, multiple rectangular negative electrodes 211b, and multiple separators 214. Both the positive electrodes 211a and 211b include protruding tab portions and portions other than the tabs. A positive electrode active material layer is formed on the portion of one side of the positive electrode 211a outside the tabs, and a negative electrode active material layer is formed on the portion of one side of the negative electrode 211b outside the tabs.

[0283] The positive electrode 211a and the negative electrode 211b are stacked in such a way that the surfaces of the positive electrode 211a that do not form a positive electrode active material layer are in contact with each other, and the surfaces of the negative electrode 211b that do not form a negative electrode active material layer are in contact with each other.

[0284] Furthermore, an insulator 214 is provided between the surface of the positive electrode 211a where the positive electrode active material layer is formed and the surface of the negative electrode 211b where the negative electrode active material layer is formed. For convenience, in Figure 16A The isolated body 214 is represented by a dashed line.

[0285] In addition, such as Figure 16B As shown, multiple positive electrodes 211a are electrically connected to wire 212a in junction 215a. Multiple negative electrodes 211b are electrically connected to wire 212b in junction 215b.

[0286] Next, refer to Figure 15B1 , Figure 15B2 , Figure 15C , Figure 15D Description of outer packaging 251.

[0287] The outer packaging 251 has a film shape and is folded in such a way that the positive electrode 211a and the negative electrode 211b are sandwiched between opposing portions of the outer packaging 251. The outer packaging 251 includes a folded portion 261, a pair of sealing portions 262 and a sealing portion 263. The pair of sealing portions 262 are arranged to sandwich the positive electrode 211a and the negative electrode 211b, and can therefore also be referred to as a side seal. The sealing portion 263 includes a portion that overlaps with the wires 212a and 212b and can also be referred to as a top seal.

[0288] The portion of the outer packaging 251 that overlaps with the positive electrode 211a and the negative electrode 211b preferably has a wave-like shape with alternating ridge lines 271 and valley lines 272. The sealing portions 262 and 263 of the outer packaging 251 are preferably flat.

[0289] Figure 15B1 The cross section is shown at the portion that overlaps with edge 271. Figure 15B2 The cross section is shown at the part that overlaps with the valley bottom line 272. Figure 15B1 and Figure 15B2 The cross-section corresponding to the width direction of battery 250, positive electrode 211a and negative electrode 211b.

[0290] The distance between the end of the negative electrode 211b in the width direction and the sealing portion 262 is called distance La. When the battery 250 is bent or deformed, as described later, the positive electrode 211a and the negative electrode 211b deform in a staggered manner in the length direction. At this time, if distance La is too short, the outer packaging 251 may rub strongly against the positive electrode 211a and the negative electrode 211b, causing damage to the outer packaging 251. In particular, when the metal film of the outer packaging 251 is exposed, there is a concern that the metal film may be corroded by the electrolyte. Therefore, it is preferable to set distance La as long as possible. However, if distance La is too long, it will lead to an increase in the volume of the battery 250.

[0291] Preferably, the greater the total thickness of the stacked positive electrode 211a and negative electrode 211b, the longer the distance La between the end of the negative electrode 211b and the sealing part 262.

[0292] Specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is thickness t, the distance La is preferably 0.8 times or more and 3.0 times or less than thickness t, more preferably 0.9 times or more and 2.5 times or less, and even more preferably 1.0 times or more and 2.0 times or less. When the distance La is within the above range, a compact battery with high reliability against bending can be realized.

[0293] Furthermore, when the distance between a pair of sealing portions 262 is a distance Lb, it is preferable that the distance Lb is sufficiently larger than the width Wb of the negative electrode 211b. In this case, even when the positive electrode 211a and the negative electrode 211b come into contact with the outer packaging 251 during repeated bending or other deformations of the battery 250, the positions of a portion of the positive electrode 211a and the negative electrode 211b can be offset in the width direction, thus effectively preventing friction between the positive electrode 211a and the negative electrode 211b and the outer packaging 251.

[0294] For example, the difference between the distance Lb (i.e., the distance between a pair of sealing portions 262) and the width Wb of the negative electrode 211b is preferably more than 1.6 times and less than 6.0 times the total thickness t of the positive electrode 211a and the negative electrode 211b, more preferably more than 1.8 times and less than 5.0 times, and even more preferably more than 2.0 times and less than 4.0 times.

[0295] In other words, the distance Lb, width Wb, and thickness t preferably satisfy the following formula 1.

[0296]

[0297] In this formula, 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.

[0298] Figure 15CThe diagram shows a cross-section including wire 212a, corresponding to the cross-section along the length of battery 250, positive electrode 211a, and negative electrode 211b. (See diagram for reference.) Figure 15C As shown, it is preferable to provide a space 273 in the folded portion 261 between the ends of the positive electrode 211a and the negative electrode 211b in the length direction and the outer packaging body 251.

[0299] Figure 15D This is a cross-sectional schematic diagram of battery 250 in a bent state. Figure 15D Equivalent to along Figure 15A The cross section of the cut-off line B1-B2 in the diagram.

[0300] When the battery 250 is bent, a portion of the outer packaging 251 located on the outer side of the bend deforms into an extension, while another portion of the outer packaging 251 located on the inner side of the bend deforms into a contraction. More specifically, the outer portion of the outer packaging 251 deforms in a manner where the wave amplitude decreases and the wave period increases. On the other hand, the inner portion of the outer packaging 251 deforms in a manner where the wave amplitude increases and the wave period decreases. When the outer packaging 251 deforms in this way, the stress applied to the outer packaging 251 by bending can be mitigated, thus the material forming the outer packaging 251 itself does not necessarily need to be stretchable. As a result, the battery 250 can be bent with relatively small force without damaging the outer packaging 251.

[0301] In addition, such as Figure 15D As shown, when the battery 250 is bent, the positions of the positive electrode 211a and the negative electrode 211b are respectively offset. At this time, the ends of the stacked positive electrode 211a and negative electrode 211b on the sealing part 263 side are fixed by the fixing member 217. Therefore, the multiple positive electrodes 211a and multiple negative electrodes 211b are offset in such a way that the offset increases as they get closer to the folded part 261. As a result, the stress applied to the positive electrode 211a and the negative electrode 211b can be mitigated, and the positive electrode 211a and the negative electrode 211b themselves do not necessarily need to be stretchable. As a result, the battery 250 can be bent without damaging the positive electrode 211a and the negative electrode 211b.

[0302] Furthermore, since a space 273 is provided between the end of the positive electrode 211a and the end of the negative electrode 211b and the outer packaging 251, the relative positions of the positive electrode 211a and the negative electrode 211b can be staggered in such a way that the ends of the positive electrode 211a and the negative electrode 211b located on the inside when the battery 250 is bent do not contact the outer packaging 251.

[0303] exist Figure 15A , Figure 15B1 , Figure 15B2 , Figure 15C and Figure 15D as well as Figure 16A and Figure 16B In the battery 250 shown, even if the battery 250 is repeatedly bent and stretched, the outer packaging, positive electrode 211a, and negative electrode 211b are not easily damaged, and the battery characteristics are not easily degraded. When the positive electrode active material described in the above embodiment is used in the positive electrode 211a included in the battery 250, a battery with excellent cycle characteristics can be achieved.

[0304] (Implementation Method 4)

[0305] In this embodiment, an example of an electronic device including a secondary battery according to one embodiment of the present invention is described.

[0306] first, Figures 17A to 17G Examples of electronic devices including the flexible secondary battery described in Embodiment 3 are shown. Examples of electronic devices including flexible secondary batteries include displays for television devices (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.

[0307] In addition, flexible secondary batteries can be assembled along the curved inner or outer walls of houses or high-rise buildings, or the interior or exterior of automobiles.

[0308] Figure 17A An example of a mobile phone is shown. The mobile phone 7400 includes a display 7402, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, etc., all assembled in a housing 7401. Furthermore, the mobile phone 7400 includes a secondary battery 7407. When the secondary battery of one embodiment of the present invention is used as the aforementioned secondary battery 7407, a lightweight mobile phone with a long service life can be provided.

[0309] Figure 17B The mobile phone 7400 is shown in a bent state. When the mobile phone 7400 is bent as a whole by using external force, the secondary battery 7407 included in the mobile phone 7400 is also bent. Figure 17C A bent secondary battery 7407 is shown. The secondary battery 7407 is a thin-film rechargeable battery. The secondary battery 7407 is bent and fixed. Furthermore, the secondary battery 7407 has wire electrodes 7408 electrically connected to a current collector 7409.

[0310] Figure 17D An example of a bracelet-type display device is shown. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. Figure 17EA bent secondary battery 7104 is shown. When the bent secondary battery 7104 is worn on a user's arm, the casing deforms, causing a change in the curvature of part or all of the secondary battery 7104. The radius of curvature of a bend at any point is the radius of the curve that best approximates the bend at that point. The reciprocal of the radius of curvature is the curvature. Specifically, part or all of the casing or the main surface of the secondary battery 7104 deforms in a range with a radius of curvature of 40 mm or more and 150 mm or less. High reliability can be maintained when the radius of curvature in the main surface of the secondary battery 7104 is 40 mm or more and 150 mm or less. When the secondary battery of one embodiment of the present invention is used as the above-described secondary battery 7104, a lightweight and long-lasting portable display device can be provided.

[0311] Figure 17F An example of a wristwatch-type portable information terminal is shown. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a strap 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, etc.

[0312] 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.

[0313] The display surface of the display unit 7202 is curved, allowing display to occur along the curved surface. Additionally, the display unit 7202 includes 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.

[0314] By using the operation button 7205, various functions can be achieved, such as setting the time, power switch, wireless communication switch, setting and canceling silent mode, and setting and canceling power-saving mode. For example, by configuring the operating system installed in the portable information terminal 7200, the function of the operation button 7205 can be freely configured.

[0315] The portable information terminal 7200 can use short-range communication methods based on existing communication standards. For example, the portable information terminal 7200 can communicate with a wirelessly wireless headset, thereby enabling hands-free calling.

[0316] Additionally, the portable information terminal 7200 includes 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 utilizing the input / output terminal 7206.

[0317] The display unit 7202 of the portable information terminal 7200 includes a secondary battery according to one embodiment of the present invention. When 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, it can be used in a bent state... Figure 17E The secondary battery 7104 shown is disposed in the housing 7201. Alternatively, the secondary battery 7104 may be disposed in the strap 7203, allowing it to be bent.

[0318] The portable information terminal 7200 preferably includes a sensor. For example, a fingerprint sensor, pulse sensor, body temperature sensor, or other human body sensor, touch sensor, pressure sensor, accelerometer, etc., are preferably installed as the sensor.

[0319] Figure 17G 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 include a touch sensor in the display unit 7304 and be used as a portable information terminal.

[0320] The display surface of the display unit 7304 is curved, allowing display to occur along the curved surface. The display state of the display device 7300 can be changed using short-range communication or other methods based on existing communication standards.

[0321] The display device 7300 includes input / output terminals, allowing it to directly send data to or receive data from other information terminals via connectors. Additionally, it can be charged via the input / output terminals. Alternatively, charging can be performed wirelessly without utilizing the input / output terminals.

[0322] When the secondary battery of one embodiment of the present invention is used as the secondary battery included in the display device 7300, a lightweight display device with a long service life can be provided.

[0323] then, Figure 18A and Figure 18B An example of a foldable tablet terminal is shown. Figure 18A and Figure 18B The illustrated tablet terminal 9600 includes a housing 9630a, a housing 9630b, a movable part 9640 connecting the housings 9630a and 9630b, a display unit 9631, a display mode switching switch 9626, a power 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 18A The tablet terminal 9600 is shown in the open state. Figure 18B The tablet terminal 9600 is shown in its closed state.

[0324] The tablet terminal 9600 includes a power storage unit 9635 inside the housings 9630a and 9630b. The power storage unit 9635 is disposed in the housings 9630a and 9630b through the movable part 9640.

[0325] A portion of the display unit 9631 can be a touchscreen area, and data can be input when the displayed operation keys are touched. Keyboard buttons can be displayed on the display unit 9631 by touching the keyboard display / non-display toggle button on the touchscreen using a finger or stylus.

[0326] The display mode switch 9626 can switch between portrait and landscape display, and between black-and-white and color display. The power-saving mode switch 9625 can control the display brightness based on the amount of external light detected by the light sensor built into the tablet terminal 9600 when the tablet terminal 9600 is in use. In addition to the light sensor, the tablet terminal may also include other detection devices such as a gyroscope and an accelerometer for detecting tilt.

[0327] exist Figure 18B The tablet terminal 9600 is closed. The tablet terminal includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. A secondary battery according to one embodiment of the present invention is used as the energy storage unit 9635.

[0328] The tablet terminal 9600 is foldable, so the outer casings 9630a and 9630b can be folded over each other when not in use. This protects the display unit 9631 and improves the durability of the tablet terminal 9600. By using a power storage unit 9635 that includes a high-capacity, high-cycle-performance secondary battery according to one embodiment of the present invention, a tablet terminal 9600 capable of long-term use can be provided.

[0329] Figure 18A and Figure 18B The tablet terminal shown may also have the following functions: displaying various types of information (e.g., still images, moving images, text images); displaying calendars, dates, or times on the display; touch input for touch input operations or editing of information displayed on the display; control processing through various software (programs); etc.

[0330] The solar cell 9633, mounted on the surface of the tablet terminal, can supply power to the touchscreen, display unit, and image signal processing unit. Note that the solar cell 9633 can be disposed on one or both surfaces of the housing 9630 and can efficiently charge the energy storage unit 9635.

[0331] Reference Figure 18C The block diagram Figure 18B The structure and operation of the charge / discharge control circuit 9634 shown are explained. Figure 18C 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, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to... Figure 18B The charging and discharging control circuit 9634.

[0332] 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 the voltage required to charge the energy storage unit 9635. When the display unit 9631 is operating using power from the solar cell 9633, switch SW1 is turned on, and converter 9637 boosts or bucks the power to the voltage required by the display unit 9631. When the display unit 9631 is not displaying anything, SW1 is turned off and SW2 is turned on to charge the energy storage unit 9635.

[0333] Note that the solar cell 9633 is shown as an example of a power generation unit, but one embodiment of the invention is not limited to this example. Other power generation units, such as piezoelectric elements or thermoelectric conversion elements, can also be used to charge the energy storage unit 9635. For example, a contactless power transmission module capable of wirelessly (contactlessly) transmitting and receiving power to charge the battery, or a combination of other charging methods, can also be used.

[0334] Figure 19 Other examples of electronic devices are shown. Figure 19 In this context, the display device 8000 is an example of an electronic device that includes a secondary battery 8004 according to one 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 one embodiment of the present invention is disposed in the housing 8001. The display device 8000 can receive power from commercial power sources. Alternatively, the display device 8000 can use the power stored in the secondary battery 8004. Therefore, even when power supply from commercial power sources is unavailable due to power outages or other reasons, the display device 8000 can operate by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power supply.

[0335] As the display unit 8002, semiconductor display devices such as liquid crystal display devices, light-emitting devices that provide light-emitting elements such as organic EL elements in each pixel, electrophoretic display devices, digital micromirror devices (DMD), plasma display panels (PDP), or field emission displays (FED) can be used.

[0336] In addition to display devices for receiving television broadcasts, the scope of display devices also includes all display devices for displaying information, such as display devices for personal computers and display devices for advertising.

[0337] exist Figure 19 In this example, the recessed lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, and a secondary battery 8103, etc. Although Figure 19 The illustration shows a secondary battery 8103 housed within a ceiling 8104 containing a housing 8101 and a light source 8102; however, the secondary battery 8103 can also be housed within the housing 8101. The lighting device 8100 can receive power from a commercial power source. Alternatively, the lighting device 8100 can use power stored in the secondary battery 8103. Therefore, even when power supply from a commercial power source is unavailable due to power outages or other reasons, the lighting device 8100 can operate by using the secondary battery 8103 of one embodiment of the present invention as an uninterruptible power source.

[0338] In addition, although Figure 19 The illustration shows an inlaid lighting device 8100 installed on the ceiling 8104, but in one embodiment of the present invention, the secondary battery can be used for inlaid lighting devices installed outside the ceiling 8104, such as on a side wall 8105, floor 8106, or window 8107. Alternatively, the secondary battery can be used for tabletop lighting devices, etc.

[0339] As the light source 8102, an artificial light source that uses electricity to emit light can be used. Specifically, examples of the aforementioned artificial light sources include incandescent bulbs, fluorescent lamps, and other discharge lamps, as well as light-emitting elements such as LEDs or organic EL elements.

[0340] exist Figure 19 In this context, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device including a secondary battery 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, and a secondary battery 8203, etc. Although Figure 19 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. Alternatively, the air conditioner can 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 supply from a commercial power source is unavailable due to power outages or other reasons, the air conditioner can still operate by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power supply.

[0341] In addition, although Figure 19 The example shown is a split-type air conditioner that includes an indoor unit and an outdoor unit, but the secondary battery of one embodiment of the present invention can also be used in an air conditioner that has the functions of an indoor unit and an outdoor unit in one housing.

[0342] exist Figure 19 In this context, the electric refrigerator / freezer 8300 is an example of an electronic device using a secondary battery 8304 according to one embodiment of the present invention. Specifically, the electric refrigerator / freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, and a secondary battery 8304, etc. Figure 19 In this design, a secondary battery 8304 is disposed inside the housing 8301. The electric refrigerator / freezer 8300 can receive power from a commercial power source. Alternatively, the electric refrigerator / freezer 8300 can use the power stored in the secondary battery 8304. Therefore, even when power supply from a commercial power source is unavailable due to a power outage or other reasons, the electric refrigerator / freezer 8300 can be operated by using the secondary battery 8304 of one embodiment of the present invention as an uninterruptible power source.

[0343] 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 power utilization rate) is low, electricity can be stored in secondary batteries, thereby reducing power utilization during periods when electronic devices are used. For example, in the case of an electric refrigerator / freezer 8300, at night when the temperature is low and the refrigerator door 8302 and freezer door 8303 are not opened or closed, electricity can be stored in secondary battery 8304. On the other hand, during the day when the temperature is high and the refrigerator door 8302 and freezer door 8303 are opened or closed, secondary battery 8304 can be used as an auxiliary power source, thereby suppressing daytime power utilization.

[0344] According to one embodiment of the present invention, the secondary battery can exhibit excellent cycle characteristics. Furthermore, according to one embodiment of the present invention, a high-capacity secondary battery can be achieved, while the secondary battery itself can be miniaturized and lightweight. Therefore, by using 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.

[0345] (Implementation Method 5)

[0346] In this embodiment, an example of a vehicle including a secondary battery according to one embodiment of the present invention is described.

[0347] By using secondary batteries in vehicles, it is possible to manufacture a new generation of clean energy vehicles, such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs).

[0348] Figures 20A to 20C An example of a vehicle using a secondary battery according to one embodiment of the present invention is shown. Figure 20A The illustrated vehicle 8400 is an electric vehicle powered by an electric motor. Alternatively, vehicle 8400 is a hybrid vehicle capable of appropriately using an electric motor or an engine. By using one embodiment of the invention, a vehicle with a long driving range can be realized. Vehicle 8400 includes a secondary battery. As a secondary battery, [the battery can be used to...] Figure 5C and Figure 5D The secondary battery modules shown are arranged on the floor of the vehicle for use. Additionally, 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 is used not only to power the electric motor 8406, but also to supply power to lighting devices such as the headlights 8401 or interior lights (not shown).

[0349] The secondary battery can also supply power to display devices such as the speedometer and tachometer in the car 8400. Furthermore, the secondary battery can supply power to semiconductor devices such as the navigation system in the car 8400.

[0350] Figure 20B The image shows a car 8500 including a secondary battery. The car 8500 can be charged by receiving power from an external charging device using a plug-in or contactless power supply method. Figure 20BIn this embodiment, a ground-mounted charging device 8021 is used to charge a secondary battery 8024 included in a vehicle 8500 via a cable 8022. During charging, the charging method and connector specifications can appropriately adopt methods specified by CHAdeMO (registered trademark) or Combined Charging System. The ground-mounted charging device 8021 can also be a power source for charging stations installed in commercial facilities or for home use. For example, by utilizing plug-in technology, power can be supplied from an external source to charge the secondary battery 8024 included in the vehicle 8500. AC power can be converted to DC power using a converter such as an AC / DC converter for charging.

[0351] Additionally, although not illustrated, the vehicle may also include a power receiving device, allowing it to be charged without contact by receiving power from a ground-based power supply. When using a contactless power supply system, by assembling the power supply device within the road or exterior wall, charging can be performed both while the vehicle is parked and while it is in motion. Furthermore, this contactless power supply system can be applied to 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.

[0352] Figure 20C An example of a two-wheeled vehicle using a secondary battery according to one embodiment of the present invention is shown. Figure 20C 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.

[0353] In addition, Figure 20C In the illustrated miniature motorcycle 8600, the secondary battery 8602 can be stored in the under-seat storage section 8604. Even if the under-seat storage section 8604 is small, the secondary battery 8602 can still be stored in it. Preferably, the secondary battery 8602 is removable, so that it can be moved indoors when charging and stored away before riding.

[0354] According to one embodiment of the present invention, the secondary battery can have excellent cycle characteristics and its capacity can be increased. This allows for a smaller and lighter secondary battery. The smaller size and lighter weight of the secondary battery itself contribute to vehicle weight reduction, thereby extending driving range. Furthermore, the secondary battery included in the vehicle can be used as a power source outside the vehicle. In this case, for example, the use of commercial power sources during peak electricity demand periods can be avoided. Avoiding the use of commercial power sources during peak electricity demand periods helps save energy and reduce carbon dioxide emissions. Moreover, if the cycle characteristics are excellent, the secondary battery can be used for a longer period, thereby reducing the use of rare metals such as cobalt.

[0355] This implementation method can be appropriately combined with other implementation methods.

[0356] [Example 1]

[0357] In this embodiment, cobalt is used as the transition metal in the first region of the positive electrode active material. Furthermore, positive electrode active materials manufactured by adding magnesium and fluorine to the starting materials, and a comparative example of positive electrode active materials manufactured without adding magnesium and fluorine, are prepared, and their characteristics are analyzed. In addition, the cycling characteristics are evaluated by varying the concentrations of magnesium and fluorine added to the starting materials.

[0358] <Preparation of the positive electrode active material of samples 1 to 6>

[0359] The positive electrode active materials for samples 1 to 6 were prepared by varying the concentrations of the magnesium and fluorine sources. Lithium carbonate and cobalt oxide were used as common starting materials. Magnesium oxide and lithium fluoride were used as different additive starting materials for each sample.

[0360] In Sample 1, magnesium oxide and lithium fluoride were added to the starting material in such a manner that magnesium comprised 0.5 atomic% and fluorine comprised 1 atomic% relative to the cobalt contained in the common starting material. Hereinafter, this is described as "In Sample 1, 0.5 mol% MgO and 1 mol% LiF were used as the added starting material".

[0361] Therefore, in this specification, the amount of starting material added is expressed as atomic% or mol% relative to the transition metal contained in the common starting material. Samples 2 and later are also expressed in the same manner.

[0362] In Sample 2, 0.5 mol% MgO and 0.5 mol% LiF (relative to cobalt) were used as starting materials. In Sample 3, 0.5 mol% MgO and 2 mol% LiF were used as starting materials. In Comparative Example Sample 4, 1 mol% LiF was used as a starting material without the addition of magnesium. In Comparative Example Sample 5, 0.5 mol% MgO was used as a starting material without the addition of fluorine. In Comparative Example Sample 6, neither magnesium nor fluorine was added. Table 1 shows the common starting materials and additional starting materials for each sample.

[0363] [Table 1]

[0364]

[0365] Positive electrode active material was obtained from each of the above six samples through the same steps as the manufacturing method described in Embodiment 1: mixing of starting materials, first heating, cooling, screening, second heating, cooling, and recovery. The particles produced during the above steps and the positive electrode active material after the above steps were analyzed as follows.

[0366] <STEM-EDX>

[0367] In Sample 1 and Sample 5 (comparative examples), the cross-section near the surface of the particles before the second heating was analyzed using STEM-EDX. Figures 22A to 22C The image shown is a STEM-EDX image of sample 1 before the second heating. Figures 23A to 23C The image shown is a STEM-EDX image of sample 5 (a comparative example) before the second heating. Figure 22A and Figure 23A The image shows a STEM image. Figure 22B and Figure 23B The image shows a surface analysis of magnesium. Figure 22C and Figure 23C The image shows a surface analysis of fluorine.

[0368] like Figure 22B As shown, in sample 1, which contains magnesium and fluorine as starting materials, a certain degree of magnesium segregation was also observed near the particle surface before the second heating. The segregated region was approximately 1 nm to 2 nm from the particle surface.

[0369] On the other hand, such as Figure 23B As shown in the EDX surface analysis image, no magnesium segregation was observed near the surface in sample 5, which was a starting material containing magnesium but not fluorine.

[0370] In addition, such as Figure 22C and Figure 23CAs shown, almost no fluorine was observed inside the positive electrode active material in both Sample 1 and Sample 5. This can be attributed to the fact that fluorine, a light element, is not easily detected by EDX.

[0371] X-ray photoelectron spectroscopy (XPS)

[0372] Next, in Sample 1 and Sample 5 (comparative examples), the amount of magnesium near the surface of the positive electrode active material before and after the second heating was determined.

[0373] The conditions for XPS analysis are as follows.

[0374] Measuring device: Quantera II manufactured by PHI

[0375] X-ray source: Monochromatic Al (1486.6 eV)

[0376] Detection area: 100μmφ

[0377] Detection depth: approximately 4 to 5 nm (flight angle of 45°)

[0378] Measurement spectrum: Broad spectrum, Li1s, Co2p, Ti2p, O1s, C1s, F1s, S2p, Ca2p, Mg1s, Na1s, Zr3d

[0379] Table 2 shows the results of quantifying the concentration of each element using XPS. The quantification accuracy is approximately ±1 atomic%. The detection limit is approximately 1 atomic%, but there are differences for individual elements. Because the Mg Auger peak from waveform separation was removed in Ca, the quantification error is larger than usual.

[0380] Table 3 shows the calculated proportions of each element when the cobalt content is 1.

[0381] [Table 2]

[0382]

[0383]

[0384]

[0385] [Table 3]

[0386]

[0387]

[0388]

[0389] Figure 24 A graph showing the presence ratio of magnesium in the elements shown in Table 3.

[0390] As shown in Table 2, Table 3 and Figure 24 As shown, in sample 1, which contains magnesium and fluorine as starting materials, magnesium near the surface of the positive electrode active material was present even before the second heating, as measured by XPS. After the second heating, the amount of magnesium near the surface of the positive electrode active material further increased.

[0391] In other words, it can be considered that magnesium segregation proceeds on the surface of the positive electrode active material through the second heating. Therefore, it can be confirmed that the positive electrode active material of sample 1 includes a first region inside and a second region on the surface, the first region containing lithium cobalt oxide and the second region containing magnesium.

[0392] On the other hand, in sample 5, which contained only magnesium and no fluorine as the starting material, the amount of magnesium near the surface of the positive electrode active material before and after the second heating was below the detection limit. That is to say, unexpectedly, it is known that the fluorine contained in the starting material has the effect of causing magnesium to segregate on the surface of the positive electrode active material.

[0393] <Cyclic Characteristics>

[0394] Next, coin-shaped secondary batteries of CR2032 (diameter: 20 mm, height: 3.2 mm) were fabricated using the positive electrode active materials of Sample 1 before and after the second heating, Sample 5 before and after the first heating, and Samples 2, 3, 4, and 6. Their cycle characteristics were evaluated.

[0395] As the positive electrode, a positive electrode formed by means of the above-manufactured positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) in a weight ratio of 95:2.5:2.5 is applied to the current collector.

[0396] Lithium metal is used as the counter electrode.

[0397] The electrolyte used is 1 mol / L lithium hexafluorophosphate (LiPF6). The electrolyte is a solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7 and 2 weight% vinylene carbonate (VC).

[0398] The positive and negative electrode containers are made of stainless steel (SUS).

[0399] In the cycle characteristic test, the measurement temperature was 25℃. During charging, a constant current of 68.5 mA / g per unit weight of the active material was used at an upper limit voltage of 4.6V, followed by constant voltage charging until the current density reached 1.4 mA / g. During discharging, a constant current of 68.5 mA / g per unit weight of the active material was used at a lower limit voltage of 2.5V. 30 charge-discharge cycles were performed.

[0400] Figure 25A and Figure 25B This is a graph showing the cycle characteristics of a secondary battery using the positive electrode active material before and after the second heating of Sample 1 and before and after the first heating of Sample 5. Figure 25A This is a graph showing the energy density when charging at 4.6V. Figure 25B This is a graph showing the energy density retention rate when charging at 4.6V. Energy density is the product of discharge capacity and average discharge voltage.

[0401] like Figure 25A and Figure 25B As shown, in sample 1, which contains magnesium and fluorine added as starting materials, the cycling characteristics are significantly improved by a second heating process. Its energy density is also good.

[0402] As can be seen from the XPS results above, this can be attributed to the increased amount of magnesium present near the surface of the positive electrode active material due to the second heating process.

[0403] On the other hand, in sample 5, which contained only magnesium as the starting material, no significant difference in cycling characteristics was observed before and after the second heating.

[0404] Figure 26 and Figure 27 A graph showing the cycle characteristics of secondary batteries using the positive electrode active materials of samples 1 to 6 after a second heating is presented. Figure 26 This is a graph showing the energy density when charging at 4.6V. Figure 27 This is a graph showing the energy density retention rate when charging at 4.6V.

[0405] like Figure 26 and Figure 27 As shown, the cycling characteristics of sample 4 (comparative example) with only fluorine added as a starting material and sample 5 (comparative example) with only magnesium added are lower than those of sample 6 (comparative example) without magnesium and fluorine added.

[0406] On the other hand, samples 1 to 3, which contained magnesium and fluorine in their starting materials, exhibited good cycling characteristics. Sample 1, with a magnesium to fluorine atomic ratio of 1:2, showed the best cycling characteristics. Sample 2, with a magnesium to fluorine atomic ratio of 1:4, also showed good cycling characteristics. Figure 26As shown, it not only has good cycle characteristics, but also good energy density.

[0407] It can be seen that by adding magnesium and fluorine to the starting material in this way, a positive electrode active material with good cycle characteristics can be obtained. In addition, the preferred atomic ratio of magnesium and fluorine contained in the starting material is Mg:F = 1:x (1.5≤x≤4), and it can be seen that the most preferred ratio is about Mg:F = 1:2.

[0408] <Preparation of the positive electrode active material of samples 7 and 8>

[0409] Next, the positive electrode active materials of samples 7 and 8 were prepared by changing the amount of magnesium and fluorine added while keeping the ratio of magnesium to fluorine constant (Mg:F = 1:2).

[0410] In Sample 7, 1 mol% MgO and 2 mol% LiF were used as starting materials. In Sample 8, 2 mol% MgO and 4 mol% LiF were used as starting materials. In Samples 7 and 8, the starting materials were mixed, first heated, cooled, screened, second heated, cooled, and recovered in the same manner as described in Embodiment 1. Thus, a positive electrode active material and a secondary battery were manufactured.

[0411] Table 4 shows the common starting materials and added starting materials of samples 1, 7, and 8, where the atomic ratio of magnesium to fluorine in the raw materials is Mg:F = 1:2, and sample 6, which is used as a comparative example and does not contain magnesium or fluorine.

[0412] [Table 4]

[0413]

[0414] <Cyclic Characteristics>

[0415] Figure 28A and Figure 28B The graph shows the cycle characteristics of secondary batteries using the positive electrode active materials of Sample 1, Sample 7, Sample 8 and Sample 6 (comparative example). Figure 28A This is a graph showing the energy density when charging at 4.6V. Figure 28B This is a graph showing the energy density retention rate when charging at 4.6V.

[0416] like Figure 28A and Figure 28B As shown, samples with a magnesium:fluorine atomic ratio of Mg:F = 1:2 exhibited good cycling characteristics. Among them, sample 7, using 1 mol% MgO and 2 mol% LiF as starting materials, showed the best cycling characteristics, retaining 93% of its energy density after 30 cycles. Furthermore, as... Figure 28AAs shown, it not only has good cycle characteristics, but also good energy density.

[0417] [Example 2]

[0418] This embodiment shows the results of comparing a positive electrode active material including a second region formed by magnesium segregation and a positive electrode active material including a magnesium oxide layer formed by external covering.

[0419] <Including the positive electrode active material in the second region formed through segregation>

[0420] As a positive electrode active material including a second region formed by magnesium segregation, Sample 7 of Example 1 was used as the starting material for addition, which used 1 mol% MgO and 2 mol% LiF.

[0421] <Including positive electrode active materials such as MgO formed through external coating>

[0422] As positive electrode active materials including a magnesium oxide layer formed by external coating, samples 9 (comparative example) and 10 (comparative example) are used, in which magnesium oxide is coated onto lithium cobalt oxide by polygonal barrel sputtering. The manufacturing methods of samples 9 (comparative example) and 10 (comparative example) are described below.

[0423] Lithium cobalt oxide (trade name: C-10N) manufactured by Nippon Chemical Industries, Ltd. was used. Magnesium oxide was used as the target in a polygonal barrel sputtering process. The power was set to 450 W, and Ar and O2 were used as the sputtering gases to form the film. The partial pressures of Ar and O2 were 0.6 Pa and 0.5 Pa, respectively. The processing time for sample 9 was 36 minutes, and the processing time for sample 10 was 180 minutes.

[0424] STEM observations after polygonal barrel sputtering revealed a magnesium oxide layer of approximately 1 nm to 3 nm on the surface of the positive electrode active material in sample 9. In sample 10, a magnesium oxide layer of approximately 6 nm to 8 nm was deposited on the surface of the positive electrode active material.

[0425] Then, samples 9 and 10 were heated at 800°C for 2 hours in the same manner as the second heating described in Embodiment 1. The heating rate was 200°C / h, and dry air with a dew point of -109°C was passed through at a rate of 10 L / min.

[0426] Table 5 shows the conditions of samples 7, 9 (comparative examples), and 10 (comparative examples) compared in this embodiment.

[0427] [Table 5]

[0428]

[0429] <STEM>

[0430] The cross-sections of the positive electrode active material of samples 7 and 10 (comparative examples) were observed using STEM. Figure 29A and Figure 29B STEM images of sample 7, including the second region formed by segregation, are shown. Figure 30A and Figure 30B STEM images of sample 10 (comparative example) including a magnesium oxide layer formed by external coating are shown.

[0431] In sample 7, based on differences in image brightness, it can be observed that the first and second regions are different areas. For example... Figure 29A and Figure 29B As shown, in sample 7, which includes a second region formed by segregation, a second region of about 1 nm to 2 nm was observed.

[0432] In addition, such as Figure 30A and Figure 30B As shown, in sample 10 (comparative example), a magnesium oxide layer can be observed to form on lithium cobalt oxide based on differences in image brightness, etc. In sample 10 (comparative example), a magnesium oxide layer of approximately 8 nm was observed.

[0433] In Sample 7 and Sample 10 (comparative examples), at least a portion of the orientations of cations and anions in different layers are aligned, and the crystal orientations of the first region and the second region are aligned.

[0434] <Charge and discharge characteristics>

[0435] The positive electrode active materials of Sample 7, Sample 9 (comparative example) and Sample 10 (comparative example) were used to manufacture secondary batteries in the same manner as in Example 1, and their charge-discharge characteristics were evaluated. Figure 31A , Figure 31B and Figure 31C The charge-discharge characteristics of secondary batteries using positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example) are shown respectively.

[0436] like Figures 31A to 31C As shown, compared with samples 9 and 10, which include a magnesium oxide layer formed by polygonal barrel sputtering, sample 7, which includes a second region formed by magnesium segregation, has a larger capacity and exhibits better charge-discharge characteristics.

[0437] Next, in Figure 32A and Figure 32BThe results show the evaluation of the cycle characteristics of secondary batteries using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example). The cycle characteristic tests were conducted in the same manner as in Example 1.

[0438] Figure 32A This is a graph showing the energy density when charging at 4.6V. Figure 32B This is a graph showing the energy density retention rate when charging at 4.6V. (Example) Figure 32B As shown, compared to samples 9 and 10, which include a magnesium oxide layer formed by polygonal barrel sputtering, sample 7, which includes a second region formed by segregation, exhibits very good cycling characteristics. Figure 32A As shown, sample 7 also has good energy density.

[0439] Therefore, it can be seen that compared with the magnesium oxide layer formed by polygonal barrel sputtering, the second region formed by magnesium segregation contributes to good charge-discharge characteristics and cycle characteristics.

[0440] Based on the above results, it can be estimated that, compared with the magnesium oxide layer covering the outside of the lithium cobalt oxide particles, the magnesium segregation in the starting material beforehand, forming a magnesium-containing region on the surface, contributes to the stabilization of the crystalline structure of lithium cobalt oxide.

[0441] [Example 3]

[0442] In this embodiment, the characteristics of the positive electrode active material, including the second region formed by magnesium segregation, were investigated through various analyses.

[0443] <Positive electrode active material to be analyzed>

[0444] Sample 7 from Example 1, which used 1 mol% MgO and 2 mol% LiF as starting materials, was used as the analytical sample in this example.

[0445] <STEM, FFT>

[0446] Figures 33A to 33C as well as Figures 34A to 34C The image shows a STEM-FFT image of a cross section near the surface of the positive electrode active material of sample 7, including a second region formed by segregation. Figure 33A These are STEM images of the vicinity of the positive electrode active material. Figure 33B Is Figure 33A An FFT (Fast Fourier Transform) image of the region represented by FFT1. For example... Figure 33C As shown, Figure 33B The bright spots in the FFT image are designated as A, B, C, and O.

[0447] The measured values ​​of the bright spots in the FFT image of the region represented by FFT1 are: OA = d = 0.20 nm, OB = d = 0.24 nm, and OC = d = 0.25 nm. Additionally, ∠AOB = 53°, ∠BOC = 74°, and ∠AOC = 127°.

[0448] The above results are close to those obtained from the magnesium oxide (MgO) data (ICDD45-0945) from the International Centre for Diffraction Data (ICDD), where OA(200) is d = 0.21 nm, OB(1-11) is d = 0.24 nm, OC(-1-11) is d = 0.24 nm, ∠AOB = 55°, ∠BOC = 70°, and ∠AOC = 125°. Therefore, the region represented by FFT1 is a region with a rock-salt type crystalline structure and is the image of the incident

[011] .

[0449] Figure 34A yes Figure 33A STEM image of the vicinity of the positive electrode active material. Figure 34B Shown in Figure 34A An FFT image of the region represented by FFT2. For example... Figure 34C As shown, Figure 34B The bright spots in the FFT image are designated as A, B, C, and O.

[0450] The measured values ​​of the bright spots in the FFT image of the region represented by FFT2 are: OA = d = 0.24 nm, OB = d = 0.20 nm, and OC = d = 0.45 nm. Additionally, ∠AOB = 25°, ∠BOC = 53°, and ∠AOC = 78°.

[0451] The above results are close to those obtained from the lithium cobalt oxide (LiCoO2) data (ICDD50-0653) in the ICDD database, where OA(101) is d = 0.24 nm, OB(104) is d = 0.20 nm, OC(003) is d = 0.47 nm, ∠AOB = 25°, ∠BOC = 55°, and ∠AOC = 80°. Therefore, it can be concluded that the region represented by FFT2 is the region containing lithium cobalt oxide and is the image of the

[010] incident region.

[0452] In addition, according to Figure 33A and Figure 34A The STEM images show that the image brightness of the first region and the second region is different, and that the crystal orientation of the first region and the crystal orientation of the second region are aligned.

[0453] <STEM-EDX>

[0454] Next, in Figures 35A to 35C , Figure 36 , Figures 37A1 to 37B2 The results of the analysis of the surface area and crystal defects of sample 7 using STEM-EDX are shown.

[0455] Figures 35A to 35C The results of STEM-EDX analysis near the surface of the positive electrode active material in sample 7 are shown. Figure 35A Showing STEM images, Figure 35B The image shows a surface analysis of magnesium. Figure 35C The image shows a surface analysis of fluorine.

[0456] Sample 1, as shown in Example 1, was prepared with 0.5 mol% MgO and 1 mol% LiF added as starting materials. Figures 22A to 22C Compared to sample 7, which was started with 1 mol% MgO and 2 mol% LiF, the results showed improvement. Figures 35A to 35C Magnesium was clearly observed near the surface of the positive electrode active material. This result supports the findings of Example 1, namely that the greater the amount of magnesium near the surface of the positive electrode active material, the better the cycle characteristics.

[0457] Figure 36 This is a cross-sectional TEM image of the area near the crystallization defects in the positive electrode active material of sample 7. Figure 36 In crystallization defect 1001, a portion with a brightness different from the other portions was observed and was considered a crystallization defect.

[0458] Figures 37A1 to 37B2 Show Figure 36 STEM-EDX analysis results of crystallization defect 1001.

[0459] Figure 37A1 The STEM image of crystal defect 1001 is shown. Figure 37A2 The image shows a surface analysis of magnesium. Figure 37B1 The image shows a surface analysis of fluorine. Figure 37B2 The image shows a surface analysis of zirconium.

[0460] like Figure 37A2 As shown, magnesium segregation was observed in and near the crystal defects of the positive electrode active material in sample 7. Therefore, it can be concluded that sample 7 is a positive electrode active material that includes a second region not only near the surface but also within it. Furthermore, as... Figure 37B2 As shown, more zirconium segregation was also observed within the second region. Since a ball mill was used in the mixing of the starting materials, and zirconium was used as a material in that ball mill, it is possible that zirconium was incorporated into sample 7. Furthermore, as... Figure 37B1 As shown, almost no fluorine was detected inside the second region. This can be attributed to the fact that fluorine, a light element, is not easily detected by EDX.

[0461] <ToF-SIMS>

[0462] Next, ToF-SIMS was used to analyze the positive electrode active material of sample 7, including the second region formed by segregation, to investigate the depth-direction distribution of magnesium and fluorine. Figure 38 The analysis results are shown.

[0463] Multiple particles of the positive electrode active material were used as samples, and ToF-SIMS analysis and sputtering were performed alternately to analyze from the surface to the depth of the positive electrode active material. A TOF-SIMS 5-300 (manufactured by ION-TOF) was used as the measurement device. Cs was used as the ion source for sputtering. Analysis was performed within a 50 μm square area.

[0464] Figure 38 Magnesium oxide ions ([MgO2]) are shown. 2- ) and fluoride ions (F - A graph showing the intensity of [MgO2]. The horizontal axis represents the number of measurements (cycles). Since negative ions are analyzed in this measurement, [MgO2] is used as the indicator. 2- The intensity is used to evaluate the magnesium distribution. Note that each intensity is normalized to a maximum value of 1.

[0465] like Figure 38 As shown, the depth-direction distribution of magnesium and fluorine overlaps with the peak values ​​in sample 7, which includes the second region formed by magnesium segregation.

[0466] <XPS>

[0467] Next, Table 6 and Figure 39 The results of XPS analysis of the positive electrode active material of sample 7 before and after the second heating are shown. The XPS analysis was performed in the same manner as in Example 1.

[0468] Table 6 shows the results of quantifying the concentrations of each element in sample 7 using XPS. The quantification accuracy was approximately ±1 atomic%, and the detection limit was approximately 1 atomic%, with some differences for individual elements. The Mg Auger peak, which was separated by waveform, was removed from Ca, and its quantification error was larger than usual.

[0469] [Table 6]

[0470]

[0471] The quantitative values ​​in Table 6 are those that can be analyzed by XPS, with the total amount of lithium, cobalt, titanium, oxygen, carbon, fluorine, sulfur, calcium, magnesium, sodium and zirconium being 100 atomic%.

[0472] As shown in Table 6, in the sample 7 after the second heating, including the second region formed by segregation, within a depth range of 4 nm to 5 nm from the surface to the center, when the total amount of lithium, cobalt, titanium, oxygen, carbon, fluorine, sulfur, calcium, magnesium, sodium and zirconium is 100%, the magnesium concentration is 5.5 atomic and the fluorine concentration is 1.4 atomic.

[0473] When calculated with the total amount of lithium, cobalt, oxygen, fluorine, and magnesium as 100%, the magnesium concentration is 6.7% and the fluorine concentration is 1.7%.

[0474] The ratio of magnesium to fluorine concentrations is in the range of Mg:F = y:1 (3≤y≤5), more precisely, Mg:F = 3.9:1.

[0475] Next, in Figure 39 The results of surface XPS analysis of the fluorine bonding state in sample 7 after a second heating are shown. As a comparative example, the results of a sample prepared in the same manner as sample 7, using 10 mol% LiF as the starting material without the addition of magnesium, are shown. Additionally, XPS spectra of standard samples of MgF2 and LiF are also shown.

[0476] like Figure 39 As shown, in the sample where 10 mol% LiF was used as the starting material without the addition of magnesium, the peak value of the fluorine bond energy was approximately 685 eV, which is equal to that of LiF. Therefore, it can be assumed that the main bonding state of fluorine in the surface layer of the positive electrode active material is LiF. On the other hand, in sample 7, which used 1 mol% MgO and 2 mol% LiF as the starting materials and included the second region, the peak value of the fluorine bond energy in the surface layer of the positive electrode active material was above 682 eV but less than 685 eV, more precisely, 684.3 eV, which is inconsistent with MgF2 or LiF. In other words, it can be inferred that the fluorine contained in the second region of the positive electrode active material is in a bonding state other than MgF2 or LiF.

[0477] [Example 4]

[0478] In this embodiment, the results of a study on the temperature of the second heating and the atmosphere during the second heating are explained.

[0479] The temperature of the second heating

[0480] <Preparation of the positive electrode active material for samples 11 to 13>

[0481] Prepare positive electrode active materials for samples 11 to 13 with different second heating temperatures. Among the starting materials of all samples, lithium carbonate and cobalt oxide are used as common starting materials, and 1 mol% MgO and 2 mol% LiF are used as additive starting materials.

[0482] In samples 11, 12, and 13, the positive electrode active materials were prepared at second heating temperatures of 700°C, 900°C, and 1000°C, respectively, with other conditions identical to those of sample 7 in Example 1. Note that in sample 7, the second heating temperature was 800°C. Table 7 shows the second heating temperatures for each sample.

[0483] [Table 7]

[0484]

[0485] Using the positive electrode active materials of Sample 7, Samples 11 to 13, secondary batteries were manufactured in the same manner as in Example 1, and their cycle characteristics were evaluated. Figure 40A and Figure 40B The cycling characteristics of samples 7, 11 to 13 are shown. The charge and discharge conditions are the same as in Example 1.

[0486] Figure 40A This is a graph showing the energy density when charging at 4.6V. Figure 40B This is a graph showing the energy density retention rate when charging at 4.6V. (Example) Figure 40B As shown, sample 7, with a second heating temperature of 800°C, exhibits the best cycling characteristics. Samples 11 and 12, with second heating temperatures of 700°C and 900°C respectively, exhibit the second best cycling characteristics. Even in sample 13, with a second heating temperature of 1000°C, the energy density retention rate after 20 cycles is 76%. Figure 26 Compared to the result of sample 6, which showed an energy density retention rate of 63% after 20 cycles without the addition of starting materials, sample 13 can be said to exhibit good cycling characteristics.

[0487] Therefore, the temperature of the second heating is preferably 700°C or higher and 1000°C or lower, more preferably 700°C or higher and 900°C or lower, and even more preferably around 800°C.

[0488] The Second Heating Atmosphere

[0489] <Preparation of the positive electrode active material for samples 14 to 16>

[0490] The positive electrode active materials for samples 14 to 16 were prepared by changing the second heating atmosphere from a dry atmosphere to 100% oxygen. Lithium carbonate and cobalt oxide were used as common starting materials in all samples, and 1 mol% MgO and 2 mol% LiF were used as additive starting materials. The positive electrode active materials were manufactured in the same manner as those for samples 7, 12, and 13, except that the second heating atmosphere was changed to an oxygen atmosphere.

[0491] Using the positive electrode active materials of samples 14 to 16, secondary batteries were manufactured in the same manner as in Example 1, and their cycle characteristics were evaluated together with those of samples 7, 12, and 13.

[0492] Figures 41A to 41C as well as Figures 42A to 42C The graphs show the energy density and cycling characteristics of samples 7, 12 to 16. Figures 41A to 41C It's a chart of energy density. Figures 42A to 42C It is a graph of the cyclic characteristics. Figure 41A and Figure 42A The energy density and cycle characteristics of samples 14 and 7, which were heated to a second temperature of 800°C, are shown. Figure 41B and Figure 42B The energy density and cycle characteristics of samples 15 and 12 are shown when the second heating temperature is 900°C. Figure 41C and Figure 42C The energy density and cycling characteristics of samples 16 and 13, with a second heating temperature of 1000℃, are shown in Table 8. Figures 41A to 41C as well as Figures 42A to 42C The second heating atmosphere and the second heating temperature of each sample are shown.

[0493] [Table 8]

[0494]

[0495]

[0496] like Figures 41A to 41C As shown, when the second heating is performed at 800°C, 900°C and 1000°C, the second heating performed in an oxygen atmosphere contributes to good cycle characteristics compared to a dry air atmosphere.

[0497] [Example 5]

[0498] In this embodiment, the cycling characteristics of the case where magnesium and fluorine are used as starting materials are compared with the cycling characteristics of the case where elements other than magnesium or fluorine are used.

[0499] Comparison of Fluorine and Chlorine

[0500] First, the cycling characteristics of the case where magnesium and fluorine are used as starting materials are compared with those of the case where chlorine is used instead of fluorine.

[0501] <Preparation of the positive electrode active material for samples 17 and 18>

[0502] In Sample 7, 1 mol% MgO and 2 mol% LiF were used as starting materials relative to cobalt. In Sample 17, 1 mol% MgO, 1 mol% LiF, and 1 mol% LiCl were used. In Comparative Example Sample 18, 1 mol% MgO and 2 mol% LiCl were used. In Comparative Example Sample 6, no magnesium, fluorine, or chlorine were added.

[0503] In samples 7, 17, 18, and 6, positive electrode active materials were prepared in the same manner as in Example 2, and secondary batteries using them were prepared for evaluation of their cycle characteristics. The cycle characteristic tests were conducted in the same manner as in Example 1.

[0504] <Cyclic Characteristics>

[0505] Table 9 shows the starting materials added to each sample and their energy density retention rate after 20 cycles.

[0506] [Table 9]

[0507]

[0508] As shown in Table 9, the cycling performance tends to decrease when chlorine is added instead of fluorine. However, in sample 17 containing 1 mol% fluorine and 1 mol% chlorine, the energy density retention rate after 20 cycles is over 80%. Compared with the results of sample 6 without the addition of magnesium, fluorine, and chlorine, sample 17 exhibits good cycling performance.

[0509] Comparison of Magnesium with Other Metals

[0510] Next, the cycling characteristics of cases where magnesium and fluorine are used as starting materials are compared with those of cases where other metals are used instead of magnesium.

[0511] <Preparation of the positive electrode active material for samples 19 to 29>

[0512] Sample 7 of Example 1 was used as the sample in which magnesium and fluorine were used as starting materials. In Comparative Example Sample 19, 1 mol% MgO, 1 mol% TiO2, and 2 mol% LiF were used as starting materials. In Comparative Example Sample 20, 1 mol% ZrO2 and 2 mol% LiF were used as starting materials. In Comparative Example Sample 21, 1 mol% TiO2 and 2 mol% LiF were used as starting materials. In Comparative Example Sample 22, 1 mol% V2O5 and 2 mol% LiF were used as starting materials. In Comparative Example Sample 23, 1 mol% ZnO and 2 mol% LiF were used as starting materials. In Comparative Example Sample 24, 1 mol% CaO and 2 mol% LiF were used as starting materials. In Comparative Example Sample 25, 1 mol% Al2O3 and 2 mol% LiF were used as starting materials. In Comparative Example Sample 26, 1 mol% MoO2 and 2 mol% LiF were used as starting materials. In comparative example sample 27, 1 mol% SrO and 2 mol% LiF were used as starting materials. In comparative example sample 28, 1 mol% NaF and 1 mol% LiF were used as starting materials. In comparative example sample 29, 1 mol% BaO and 2 mol% LiF were used as starting materials. As a comparative example without the addition of fluorine and any metals, sample 6 of Example 1 was used.

[0513] In samples 6, 7, 19 to 29, positive electrode active materials were prepared in the same manner as in Example 1, and secondary batteries using them were prepared for evaluation of their cycle characteristics.

[0514] <Cyclic Characteristics>

[0515] Table 10 shows the starting materials added to each sample and their energy density retention rate after 20 cycles.

[0516] [Table 10]

[0517]

[0518]

[0519] As shown in Table 10, when other metals are added to replace magnesium, there is a tendency for the cycling characteristics to decrease.

[0520] Based on the above results, it can be seen that using the combination of magnesium and fluorine as an additive starting material is very effective.

[0521] According to the above embodiments, it is known that by adding magnesium and fluorine as starting materials for the positive electrode active material, magnesium segregates onto the surface of the positive electrode active material. Furthermore, it is known that the positive electrode active material, due to the presence of a good capping layer formed through segregation, can possess high capacity and high cycle performance.

[0522] Because secondary batteries incorporating this positive electrode active material have high capacity and long lifespan, they are suitable for use in portable electronic devices. Furthermore, when applied to automobiles and other vehicles, they can avoid the use of commercial power sources during peak electricity demand periods, contributing to energy savings and reduced carbon dioxide emissions.

[0523] [Example 6]

[0524] In this embodiment, the results of preparing and evaluating the positive electrode active materials using nickel, manganese, and cobalt as the transition metals of the first region are described.

[0525] <Sample 31, Sample 32>

[0526] Prepare a sample 31 containing magnesium and fluorine and a sample 32 not containing magnesium and fluorine as a comparative example.

[0527] Sample 31 is as follows: 1 atomic% magnesium and 2 atomic% fluorine were added relative to the total amount of nickel, manganese, and cobalt in the starting materials. Furthermore, the atomic ratio of nickel, manganese, and cobalt in the starting materials was Ni:Mn:Co = 1:1:1.

[0528] First, lithium carbonate (Li₂CO₃) is used as the common starting material for lithium. Nickel oxide (NiO) is used as the nickel source. Manganese oxide (MnO₂) is used as the manganese source. Cobalt oxide (Co₃O₄) is used as the cobalt source. Magnesium oxide (MgO) is used as the magnesium source for the added starting materials. Lithium fluoride (LiF) is used as the fluorine source.

[0529] LiCo 0.323 Mn 0.333 Ni 0.333 O2+MgO 0.01 LiF 0.02 The atomic ratio of each starting material was weighed.

[0530] Next, the weighed starting materials are mixed using a ball mill.

[0531] The mixed starting materials were then calcined. The calcination was carried out at 950°C for 10 hours under the following conditions: a heating rate of 200°C / h and a dry air flow rate of 10 L / min.

[0532] Through the above process, particles containing composite oxides of lithium, nickel, manganese, cobalt, fluorine, and magnesium are synthesized.

[0533] The synthesized composite oxide particles were cooled to room temperature.

[0534] The composite oxide particles were then heated. This heating was carried out in a dry air atmosphere under the following conditions: a temperature of 800°C (heating rate of 200°C / h); and a holding time of 2 hours.

[0535] The heated particles are cooled to room temperature and then ground. In this grinding process, the particles are passed through a sieve with a pore size of 53 μm.

[0536] The crushed particles were used as the positive electrode active material of sample 31.

[0537] In sample 32, LiCo 0.333 Mn 0.333 Ni 0.333 The atomic ratio of O2 was weighed for each starting material. Furthermore, calcination was performed at 1000°C. For other manufacturing conditions, refer to the manufacturing conditions of sample 31.

[0538] Table 11 shows the manufacturing conditions for samples 31 and 32.

[0539] [Table 11]

[0540]

[0541] <Cyclic Characteristics>

[0542] Next, coin-shaped secondary batteries (diameter: 20 mm, height: 3.2 mm) of CR2032 were manufactured using the positive electrode active materials of samples 31 and 32 formed in the manner described above. Their cycle characteristics were evaluated.

[0543] The positive electrode was formed as follows: a slurry containing the positive electrode active materials of samples 31 and 32, acetylene black (AB), and polyvinylidene fluoride (PVDF) in a weight ratio of 95:2.5:2.5 was coated onto an aluminum foil current collector. N-methyl-2-pyrrolidone (NMP) was used as the solvent.

[0544] Lithium metal is used as the counter electrode.

[0545] The electrolyte used is 1 mol / L lithium hexafluorophosphate (LiPF6). The electrolyte is a solution prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7 and adding 2 weight% of vinylene carbonate (VC).

[0546] The positive and negative electrode containers are made of stainless steel (SUS).

[0547] In the cycle characteristic test, the measurement temperature was 25°C. During charging, a constant current of 68.5 mA / g per unit weight of the active material was used to charge at an upper limit voltage of 4.6V. Then, constant voltage charging was performed until the current density reached 1.4 mA / g. During discharging, a constant current of 68.5 mA / g per unit weight of the active material was used to discharge at a lower limit voltage of 2.5V.

[0548] Figure 43A The discharge capacity of the secondary battery using the positive electrode active materials of samples 31 and 32 is shown when charged at 4.6V. Figure 43B The discharge capacity retention rate is shown.

[0549] Compared with the results of sample 32 without added magnesium and fluorine, sample 31 with added magnesium and fluorine showed very good cycling characteristics.

[0550] Next, the results of various analyses performed on sample 31 are shown below.

[0551] <STEM-FFT>

[0552] Figure 44A and Figure 44B as well as Figure 45A and Figure 45B STEM image showing a cross section near the surface of the positive electrode active material of sample 31. Figure 44B Is to make Figure 44A A STEM image obtained by magnifying a portion of it. Figure 45A and Figure 45B Is to make Figure 44A The HAADF-STEM image is obtained by magnifying a portion of it.

[0553] Depend on Figure 45A and Figure 45B It can be observed that the brightness of a region approximately 0.5 nm above the surface of the positive electrode active material differs from that of other regions. This can be attributed to the higher content of magnesium, an element lighter than transition metals.

[0554] Furthermore, in a region from approximately 0.5 nm to 5 nm on the surface of the positive electrode active material, a different periodicity was observed compared to the internal region. This can be attributed to the different crystal orientation in the surface region (from approximately 0.5 nm to 5 nm) compared to the internal crystal orientation.

[0555] Figure 46A Is with Figure 45B STEM images of the same range in bright field. Figure 46B Shown in Figure 46AThe Fast Fourier Transform (FFT) image of the region represented by FFT1. For example... Figure 46B As shown, a portion of the bright spots in the FFT1 image is designated as A, B, C, and O.

[0556] The measured values ​​of the bright spots in the FFT image of the region represented by FFT1 are: OA = d = 0.22 nm, OB = d = 0.25 nm, and OC = d = 0.23 nm. Additionally, ∠AOB = 58°, ∠BOC = 69°, and ∠AOC = 127°.

[0557] The above results are close to those obtained from the magnesium oxide (MgO) data (ICDD45-0945) from the International Centre for Diffraction Data (ICDD), where OA(200) is d = 0.21 nm, OB(1-11) is d = 0.24 nm, OC(-1-11) is d = 0.24 nm, ∠AOB = 55°, ∠BOC = 70°, and ∠AOC = 125°. Therefore, the region represented by FFT1 is a region with a rock-salt type crystalline structure and is the image of the incident

[011] .

[0558] Figure 46C Shown in Figure 46A An FFT image of the region represented by FFT2. For example... Figure 46C As shown, a portion of the bright spots in the FFT2 image is designated as A, B, C, and O.

[0559] The measured values ​​of the bright spots in the FFT image of the region represented by FFT2 are: OA = d = 0.25 nm, OB = d = 0.21 nm, and OC = d = 0.49 nm. Additionally, ∠AOB = 26°, ∠BOC = 57°, and ∠AOC = 83°.

[0560] The above results are close to those obtained from lithium cobalt oxide (LiCoO2) data (ICDD50-0653) in the ICDD database, where OA(10⁻¹¹) is d = 0.24 nm, OB(10⁻¹⁴) is d = 0.20 nm, OC(0003) is d = 0.47 nm, ∠AOB = 25°, ∠BOC = 55°, and ∠AOC = 80°. Therefore, the region represented by FFT2 is a region with a layered rock-salt type crystal structure and is an image with an incident angle of [-12-10].

[0561] Figure 46D Shown in Figure 46A An FFT image of the region represented by FFT3. For example... Figure 46D As shown, a portion of the bright spots in the FFT3 image is designated as A, B, C, and O.

[0562] The measured values ​​of the bright spots in the FFT image of the region represented by FFT3 are: OA = d = 0.21 nm, OB = d = 0.26 nm, and OC = d = 0.24 nm. Additionally, ∠AOB = 56°, ∠BOC = 72°, and ∠AOC = 128°.

[0563] The above results are close to those obtained from lithium cobalt oxide (LiCoO2) data (ICDD50-0653) in the ICDD database, where OA (01-14) has d = 0.20 nm, OB (10-1-2) has d = 0.23 nm, OC (1-102) has d = 0.23 nm, ∠AOB = 55°, ∠BOC = 70°, and ∠AOC = 125°. Therefore, the region represented by FFT2 is a region with a layered rock-salt type crystal structure and is the image of incident [02-21].

[0564] In other words, it can be seen that the regions represented by FFT2 and FFT3 both have a layered rock salt crystal structure, but their crystal axis directions are different from each other.

[0565] exist Figure 45A , Figure 45B and Figure 46A Within the observable range, it was observed that even with different brightness levels, the crystal orientations were roughly aligned.

[0566] Figure 47 This shows a STEM image and the structure near the surface of the positive electrode active material inferred from the results of STEM-FFT. Figure 47 In this context, M represents any one of nickel, manganese, or cobalt.

[0567] The FFT3 region inside the positive electrode active material has a layered rock salt-type crystal structure. Furthermore, the FFT3 is an incident image [02-21] observed when lithium atoms overlap with M atoms.

[0568] Furthermore, the surface region of the positive electrode active material exhibits a layered rock-salt type crystal structure in FFT2. FFT2 is an image with an incident intensity of [-12-10], showing a recurring pattern of layers of oxygen atoms, layers of M (one of nickel, manganese, or cobalt) atoms, and layers of lithium atoms. The reason for the recurring dark and bright layers in the bright-field STEM image can be attributed to the recurring patterns of M, oxygen, and lithium layers. In other words, although both FFT3 and FFT2 possess a layered rock-salt type crystal structure, their crystal axis orientations are different.

[0569] In addition, in the region of the surface layer of the positive electrode active material, FFT1, which is closer to the surface than FFT2, has a rock salt-type crystal structure and is the incident image of

[011] .

[0570] <EDX>

[0571] Next, EDX was used to analyze the cross-section near the surface of the positive electrode active material in sample 31. Figures 48A1 to 48B2 as well as Figures 49A1 to 49B2 The results are shown in the figure.

[0572] Figure 48A1 It is a HAADF-STEM image. Figure 48A2 This is a surface analysis image of oxygen. Figure 48B1 This is a surface analysis image of magnesium. Figure 48B2 This is a surface analysis image of fluorine. Figure 49A1 Is with Figure 48A1 The same HAADF-STEM image, Figure 49A2 This is a surface analysis image of manganese. Figure 49B1 This is a surface analysis image of nickel. Figure 49B2 This is a surface analysis image of cobalt.

[0573] from Figure 48B1 Magnesium segregation was observed in a region approximately 3 nm from the surface of the positive electrode active material. According to... Figure 49A2 , Figure 49B1 , Figure 49B2 Comparison revealed a region on the surface of the positive electrode active material with lower manganese content and higher nickel and cobalt content compared to its interior. This region extends approximately 5 nm from the surface and roughly overlaps with a periodic region observed in STEM images that differs from its interior.

[0574] Therefore, it can be confirmed that the positive electrode active material of sample 31 is a positive electrode active material whose surface layer includes a region containing magnesium and whose interior part includes a region with low manganese content.

[0575] Based on the above results, it can be concluded that the molar ratio of the starting materials should be set to LiNi. 1 / 3 Mn 1 / 3 Co 1 / 3 The positive electrode active material of sample 31, which is prepared by heating O2 + 1 mol% MgO + 2 mol% LiF at 800 °C, has the following characteristics.

[0576] First, the positive electrode active material of sample 31 includes a second region containing magnesium oxide in its surface layer. Inside this positive electrode active material, near the center, there is a LiNi-containing region with a layered rock-salt type crystal structure. x Mn y Co z The region of O2(x+y+z=1), near the surface, includes LiNi with a layered rock salt-type crystalline structure. a Mn b Co c The region of O2(a+b+c=1).

[0577] Internal LiNi x Mn y Co z O2 and LiNi a Mn b Co c O2 all have a layered rock salt-type crystal structure, but their crystal axis orientations are sometimes different from each other.

[0578] The content of each element is y > b, and sometimes the manganese content relative to the sum of nickel, manganese and cobalt is lower in the region near the surface.

[0579] When the positive electrode active material of sample 31 with the above characteristics is used in a secondary battery, it exhibits very good cycle characteristics.

[0580] [Example 7]

[0581] In this embodiment, the results of analysis using EELS on a positive electrode active material prepared by adding cobalt as a transition metal and adding magnesium and fluorine as starting materials are described.

[0582] Sample 7 from Example 1, which used 1 mol% MgO and 2 mol% LiF as starting materials, was used as the analytical sample in this example.

[0583] The cobalt state at six analytical points, *1 to *6, in the cross-section of sample 7 was analyzed using EELS. Figure 50 This is a STEM image of a cross-section near the surface of the positive electrode active material of sample 7 used for EELS analysis, showing analysis points *1 (approximately 1 nm from the surface), *2 (approximately 2.5 nm), and *3 (approximately 5 nm). Additionally, *4 is approximately 10 nm from the surface of the positive electrode active material, *5 is approximately 100 nm from the surface of the positive electrode active material, and *6 is located near the center of the particles in the positive electrode active material.

[0584] Table 12 and Figure 51 The EELS intensity ratios of the L2 and L3 energy levels of cobalt are shown at each analytical point. The higher the L3 / L2 ratio, the lower the valence of cobalt.

[0585] [Table 12]

[0586] Measurement area <![CDATA[L3 / L2]]> *1 4.6 *2 3.0 *3 3.2 *4 3.0 *5 2.9 *6 3.1

[0587] From Table 12 and Figure 51 It can be seen that the L3 / L2 ratio is highest at analysis point *1, which is closest to the surface of the positive electrode active material, at 4.6. The L3 / L2 ratios of analysis points *2 to *6 are lower than those of analysis point *1, and fall within the range of 2.9 to 3.2, with no significant difference between them.

[0588] Based on the above results, it can be seen that at analysis point *1, the amount of divalent cobalt present as cobalt oxide (CoO) is relatively large, and at analysis points *2 to *6, the amount of trivalent cobalt present as lithium cobalt oxide (LiCoO2) is relatively large.

[0589] Symbol Explanation

[0590] 100: Positive electrode active material; 101: First region; 102: Second region; 103: Third region; 200: Active material layer; 201: Graphene compound; 211a: Positive electrode; 211b: Negative electrode; 212a: Wire; 212b: Wire; 214: Insulator; 215a: Junction; 215b: Junction; 217: Fixing component; 250: Secondary battery; 251: Outer packaging; 261: Folded portion; 262: Sealing part; 263: Sealing part; 271: Ridge; 272: Valley line; 273: Space; 300: 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. Material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Insulator, 500: Secondary battery, 501: Positive electrode current collector, 502: Positive electrode active material layer, 503: Positive electrode, 504: Negative electrode current collector, 505: Negative electrode active material layer, 506: Negative electrode, 507: Insulator, 508: Electrolyte, 509: Outer packaging, 510: Positive electrode wire, 511: Negative electrode wire, 600: 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, 612 900: Safety valve mechanism; 910: Circuit board; 911: Label; 912: Terminal; 913: Circuit; 914: Secondary battery; 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: Winding body; 951: Terminal; 952: Terminal; 980: Secondary battery; 993: Winding body; 994: Negative electrode; 995: Positive electrode; 996: Insulator; 997: Wire electrode; 998: Wire electrode; 1001: Crystallization defect; 7100: Portable display device. 7101: Housing; 7102: Display unit; 7103: Operation button; 7104: Secondary battery; 7200: Portable information terminal; 7201: Housing; 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: Housing; 7402: Display unit; 7403: Operation button; 7404: External connection port; 7405: Speaker; 7406: Microphone; 7407: Secondary battery; 7408: Conductor electrode; 7409: Current collector; 8000: Display device; 8001: Housing.8002: Display unit, 8003: Speaker unit, 8004: Secondary battery, 8021: Charging device, 8022: Cable, 8024: Secondary battery, 8100: Lighting device, 8101: Housing, 8102: Light source, 8103: Secondary battery, 8104: Ceiling, 8105: Side wall, 8106: Floor, 8107: Window, 8200: Indoor unit, 8201: Housing, 8202: Air outlet, 8203: Secondary battery, 8204: Outdoor unit, 8300: Electric refrigerator / freezer, 8301: Housing, 8302: Refrigerator door, 8303: Freezer door, 8304: Secondary battery, 8400: Automobile, 8 401: Headlight; 8406: Electric motor; 8500: Automobile; 8600: Motorcycle; 8601: Rearview mirror; 8602: Secondary battery; 8603: Turn signal; 8604: Under-seat storage unit; 9600: Tablet terminal; 9625: Switch; 9626: Switch; 9627: Power switch; 9628: Operating switch; 9629: Fastener; 9630: Housing; 9630a: Housing; 9630b: Housing; 9631: Display unit; 9633: Solar cell; 9634: Charging / discharging control circuit; 9635: Energy storage unit; 9636: DC-DC converter; 9637: Converter; 9640: Movable part.

[0591] This application is based on Japanese Patent Application No. 2016-200835, filed with the Japan Patent Office on October 12, 2016; Japanese Patent Application No. 2017-052309, filed with the Japan Patent Office on March 17, 2017; and Japanese Patent Application No. 2017-100619, filed with the Japan Patent Office on May 22, 2017, the entire contents of which are incorporated herein by reference.

Claims

1. A lithium-ion secondary battery, comprising: A positive electrode having positive electrode active material particles, wherein the positive electrode active material particles have a first region and a second region; negative electrode; Insulator; Electrolyte; Outer packaging; The second region is located near the surface of the positive electrode active material particles; The first region contains lithium, oxygen, cobalt, and aluminum; The second region contains magnesium, cobalt, and oxygen; The first region has a layered rock salt type crystal structure; The second region has a rock salt-type crystalline structure; The second region also forms near crystal defects within the first region; The second region formed near the crystallization defect contains magnesium; The second region formed near the crystallization defect has a rock salt-type crystallization structure; In the EELS measurement in the first measurement area, there is cobalt oxide containing divalent cobalt; The crystal orientation of the first region is roughly aligned with that of the second region.

2. A lithium-ion secondary battery, comprising: A positive electrode having positive electrode active material particles, wherein the positive electrode active material particles have a first region and a second region; negative electrode; Insulator; Electrolyte; Outer packaging; The second region covers at least a portion of the first region; The first region contains lithium, oxygen, cobalt, and aluminum; The second region contains magnesium, cobalt, and oxygen; The first region has a layered rock salt type crystal structure; The second region has a rock salt-type crystalline structure; The second region also forms near crystal defects within the first region; The second region formed near the crystallization defect contains magnesium; The second region formed near the crystallization defect has a rock salt-type crystallization structure; In the EELS measurement in the first measurement area, there is cobalt oxide containing divalent cobalt; The crystal orientation of the first region is approximately aligned with the crystal orientation of the second region; If the total amount of lithium, cobalt, magnesium, oxygen and fluorine atoms on the surface of the positive electrode active material particles, as measured by X-ray photoelectron spectroscopy, is set to 100 atomic%, then the magnesium concentration is above 1 atomic% and below 16 atomic%.

3. A lithium-ion secondary battery, comprising: A positive electrode having positive electrode active material particles, wherein the positive electrode active material particles have a first region, a second region and a third region; negative electrode; Insulator; Electrolyte; Outer packaging; The first region contains lithium, oxygen, cobalt, and aluminum; The second region contains magnesium, cobalt, and oxygen; The second region is located between the first region and the third region; The third region is in contact with the second region; The first region has a layered rock salt type crystal structure; The second region has a rock salt-type crystalline structure; The second region also forms near crystal defects within the first region; The second region formed near the crystallization defect contains magnesium and cobalt; In the EELS measurements in the first measurement region, divalent cobalt was found to be more abundant than cobalt of other valences; The crystal orientation of the first region is roughly aligned with that of the second region.

4. A lithium-ion secondary battery, comprising: A positive electrode having positive electrode active material particles, wherein the positive electrode active material particles have a first region and a second region; negative electrode; Insulator; Electrolyte; Outer packaging; The first region contains lithium, oxygen, cobalt, and aluminum; The second region contains magnesium, cobalt, and oxygen; The second region is located near the surface of the positive electrode active material particles; The first region has a layered rock salt type crystal structure; The second region has a rock salt-type crystalline structure; The second region also forms near crystal defects within the first region; The second region formed near the crystallization defect contains magnesium; The second region formed near the crystallization defect has a rock salt-type crystallization structure; In the EELS measurements in the first measurement region, divalent cobalt was found to be more abundant than cobalt of other valences; The crystal orientation of the first region is roughly aligned with that of the second region.

5. A lithium-ion secondary battery, comprising: A positive electrode having positive electrode active material particles, wherein the positive electrode active material particles have a first region and a second region; negative electrode; Insulator; Electrolyte; Outer packaging; The first region contains lithium, oxygen, cobalt, and aluminum; The second region contains magnesium, cobalt, and oxygen; The second region covers at least a portion of the first region; The first region has a layered rock salt type crystal structure; The second region has a rock salt-type crystalline structure; The second region also forms near crystal defects within the first region; The second region formed near the crystallization defect contains magnesium and cobalt; In the EELS measurements in the first measurement region, divalent cobalt was found to be more abundant than cobalt of other valences; The crystal orientation of the first region is approximately aligned with the crystal orientation of the second region; If the total amount of lithium, cobalt, magnesium, oxygen and fluorine atoms on the surface of the positive electrode active material particles, as measured by X-ray photoelectron spectroscopy, is set to 100 atomic%, then the magnesium concentration is above 1 atomic% and below 16 atomic%.

6. A lithium-ion secondary battery, comprising: A positive electrode having positive electrode active material particles, wherein the positive electrode active material particles have a first region, a second region and a third region; negative electrode; Insulator; Electrolyte; Outer packaging; The first region contains lithium, oxygen, cobalt, and aluminum; The second region contains magnesium, cobalt, and oxygen; The second region is located between the first region and the third region; The third region is in contact with the second region; The first region has a layered rock salt type crystal structure; The second region has a rock salt-type crystalline structure; The second region also forms near crystal defects within the first region; The second region formed near the crystallization defect contains magnesium; In the EELS measurements in the first measurement region, divalent cobalt was found to be more abundant than cobalt of other valences; The crystal orientation of the first region is approximately aligned with the crystal orientation of the second region; If the total amount of lithium, cobalt, magnesium, oxygen and fluorine atoms on the surface of the positive electrode active material particles, as measured by X-ray photoelectron spectroscopy, is set to 100 atomic%, then the magnesium concentration is above 1 atomic% and below 16 atomic%.

7. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium oxide, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. A portion of the magnesium in the magnesium oxide is bonded to fluorine. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

8. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium oxide, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. A portion of the magnesium in the magnesium oxide is bonded to fluorine. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

9. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium oxide, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. A portion of the magnesium in the magnesium oxide is bonded to fluorine. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

10. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium oxide, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. Some of the oxygen in the magnesium oxide is replaced by fluorine. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

11. A lithium-ion secondary battery, comprising: It has a positive electrode, a negative electrode, and an electrolyte containing positively active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium oxide, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. Some of the oxygen in the magnesium oxide is replaced by fluorine. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

12. A lithium-ion secondary battery, having It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium oxide, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. Some of the oxygen in the magnesium oxide is replaced by fluorine. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

13. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, there is a region where the distribution of fluorine overlaps with the distribution of magnesium. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

14. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, there is a region where the distribution of fluorine overlaps with the distribution of magnesium. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

15. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt and a second region containing cobalt, magnesium, and fluorine. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, there is a region where the distribution of fluorine overlaps with the distribution of magnesium. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

16. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

17. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

18. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

19. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, the maximum magnesium concentration exists. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

20. A lithium-ion secondary battery, having It has a positive electrode, a negative electrode, and an electrolyte containing positively active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, the maximum magnesium concentration exists. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

21. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, the maximum magnesium concentration exists. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

22. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has an area in contact with the decomposition products of the electrolyte. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

23. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The second region has an area in contact with the decomposition products of the electrolyte. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

24. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has an area in contact with the decomposition products of the electrolyte. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

25. A lithium-ion secondary battery, having It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, the maximum magnesium concentration exists. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has an area in contact with the decomposition products of the electrolyte. The first region contains more trivalent cobalt compared to cobalt of other valences. The second region contains more divalent cobalt compared to cobalt of other valences.

26. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, the maximum magnesium concentration exists. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has an area in contact with the decomposition products of the electrolyte. The second region has more points that can be analyzed by electron energy loss spectroscopy when cobalt exists in the divalent state compared to when it exists in the trivalent state.

27. A lithium-ion secondary battery, comprising: It contains positive electrode, negative electrode and electrolyte, which are positive active material particles. In the lithium-ion secondary battery. The positive electrode active material particles contain lithium cobalt oxide. The positive electrode active material particles have a first region containing cobalt, a second region containing cobalt, magnesium, and fluorine, and a region containing aluminum. The first region is located more within the positive electrode active material particles than the second region. The first region has a layered rock salt type crystal structure. The second region has a rock salt-type crystalline structure. In the second region, the maximum magnesium concentration exists. The aluminum-containing region is located between the first region, which has a layered rock salt-type crystalline structure, and the second region, which has a rock salt-type crystalline structure. The region containing aluminum overlaps with the first region and the second region. The second region has an area in contact with the decomposition products of the electrolyte. In electron energy loss spectroscopy, the second region has an analytical point with an L3 / L2 ratio of 3.8 or higher when the L2 energy level of cobalt is L2 and the L3 energy level of cobalt is L3.

28. The lithium-ion secondary battery according to any one of claims 22 to 27, wherein the fluorine contained in the second region is in contact with the decomposition products of the electrolyte.

29. The lithium-ion secondary battery according to any one of claims 16 to 27, wherein the second region comprises magnesium oxide, a portion of which is bonded to fluorine.

30. The lithium-ion secondary battery according to any one of claims 16 to 27, wherein the second region comprises magnesium oxide, and a portion of the oxygen contained in the magnesium oxide is replaced by fluorine.

31. The lithium-ion secondary battery according to any one of claims 16 to 27, wherein in the second region, there is a region where the distribution of fluorine overlaps with the distribution of magnesium.

32. The lithium-ion secondary battery according to claim 31, wherein in the second region, the region where the distribution of fluorine overlaps with the distribution of magnesium is observed by EDX line analysis.

33. The lithium-ion secondary battery according to any one of claims 19 to 21 and 25 to 27, wherein the maximum value of the peak value of the magnesium concentration is observed by EDX line analysis.

34. The lithium-ion secondary battery according to claim 33, wherein the second region is a region where the peak value of the magnesium concentration is greater than 1 / 5 of the maximum value.

35. The lithium-ion secondary battery according to any one of claims 7 to 18 and 22 to 24, wherein the second region is a region greater than 1 / 5 of the maximum value of the magnesium peak observed in EDX line analysis of the cross-section of the positive electrode active material particles.

36. The lithium-ion secondary battery according to claim 34, wherein the second region exists from the surface of the positive electrode active material particles.

37. The lithium-ion secondary battery of claim 35, wherein the second region exists from the surface of the positive electrode active material particles.

38. The lithium-ion secondary battery according to any one of claims 7 to 27, wherein the second region comprises CoO(II).

39. The lithium-ion secondary battery according to any one of claims 7 to 27, wherein the electrolyte comprises vinylene carbonate.

40. The lithium-ion secondary battery according to any one of claims 7 to 27, wherein the electrolyte comprises lithium hexafluoride phosphate, and the electrolyte comprises ethylene carbonate, diethyl carbonate and vinylene carbonate.

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