Lithium ion secondary battery

Abstract

To provide a positive electrode active material that is used for a lithium ion secondary battery to suppress the decrease in capacity in a charging and discharging cycle.SOLUTION: In a surface layer part of a positive electrode active material, a coating layer is formed by segregation. The positive electrode active material includes a first region and a second region. The first region exists internally. The second region exists in a part of the surface layer part and the inside. The first region contains lithium, transition metal, and oxygen. The second region contains magnesium, fluorine, and oxygen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] One aspect of the present invention relates to an article, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a method for manufacturing a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic apparatus. In particular, it relates to a positive electrode active material that can be used in a secondary battery, a secondary battery, and an electronic device having the secondary battery.

[0002] Note that in this specification, the power storage device refers to all elements and devices having a power storage function. For example, it includes storage batteries (also referred to as secondary batteries) such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors.

[0003] Also, in this specification, the electronic device refers to all devices having a power storage device. An electro-optical device having a power storage device, an information terminal device having a power storage device, etc. are all electronic devices.

Background Art

[0004] In recent years, various power storage devices such as lithium ion secondary batteries, lithium ion capacitors, and air batteries have been actively developed. In particular, lithium ion secondary batteries with high output and high capacity are rapidly expanding in demand along with the development of the semiconductor industry, for portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, or next-generation clean energy automobiles such as hybrid electric vehicles (HEVs), electric vehicles ( EVs), or plug-in hybrid electric vehicles (PHEVs). The demand for rechargeable energy is rapidly expanding, It has become an essential part of the modern information society as a supply source.

[0005] The characteristics currently required for lithium-ion secondary batteries include further increased capacity, improved cycle characteristics, improved safety in various operating environments, and improved long-term reliability.

[0006] One of the methods to increase the capacity of lithium-ion secondary batteries is to increase the charging voltage, which is known For example, the capacity of lithium cobaltate, which is often used as the positive electrode active material of lithium-ion secondary batteries, is generally 155 mAh / g when the charging voltage is 4.3 V, but when the charging voltage is increased to 4.6 V, it becomes 220 mAh / g (see Fig. 21(A)).

[0007] However, it is also known that increasing the charging voltage deteriorates the cycle characteristics. For example, general lithium cobaltate has a capacity retention rate of 95% or more after 30 cycles when the charging voltage is 4.4 V, but when the charging voltage is increased to 4.6 V, the capacity retention rate after 30 cycles drops to 50% or less (see Fig. 21(B)). Therefore, in order to improve the cycle characteristics and increase the capacity of lithium-ion secondary batteries, the improvement of the positive electrode active

[0008] material is being studied (Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

Patent Document 1

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] Thus, there is still room for improvement in lithium ion secondary batteries and cathode active materials used therein in various aspects such as capacity, cycle characteristics, charge / discharge characteristics, reliability, safety, or cost.

[0011] One aspect of the present invention is to provide a cathode active material that suppresses a decrease in capacity during charge / discharge cycles when used in a lithium ion secondary battery. Or, one aspect of the present invention is to provide a high-capacity secondary battery. Or, one aspect of the present invention is to provide a secondary battery with excellent charge / discharge characteristics. Or, one aspect of the present invention is to provide a secondary battery with high safety or reliability. Or, one aspect of the present invention is to provide a novel substance, active material, power storage device, or a method for producing them.

[0012]

[0013] Note that the description of these problems does not prevent the existence of other problems. Note that one aspect of the present invention does not need to solve all of these problems. Note that it is possible to extract other problems from the description of the specification, drawings, and claims.

Means for Solving the Problems

[0014] To achieve the above object, one aspect of the present invention is characterized in that a coating layer is formed on the surface layer portion of the cathode active material by segregation.

[0015] One aspect of the present invention is a cathode active material, and the cathode active material includes a first region, a second region, ​​​​​​​​It has a first region that exists inside the positive electrode active material, and a second region that exists in the surface layer part and a part of the inside of the positive electrode active material. The first region has lithium, a transition metal, and oxygen, and the second region has magnesium, fluorine, and oxygen, and is a positive electrode active material. Also, one aspect of the present invention is a positive electrode active material. The positive electrode active material has lithium, a transition metal,

[0016] oxygen, magnesium, and fluorine, and exists on the surface of the positive electrode active material. Taking the total amount of atoms including lithium, transition metal, oxygen, fluorine, and magnesium measured by X-ray photoelectron spectroscopy as 100 atomic%, the magnesium concentration measured by X-ray photoelectron spectroscopy on the surface of the positive electrode active material is 1 atomic% or more and 16 atomic% or less, and the fluorine concentration is 0.2 atomic% or more and 4 atomic% or less, and it is a positive electrode active material. Also, one aspect of the present invention is a positive electrode active material. The positive electrode active material has lithium, a transition metal, oxygen, magnesium, and fluorine, and the ratio of the magnesium concentration to the 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), and it is a positive electrode active material.

[0017] Also, one aspect of the present invention is a positive electrode active material. The positive electrode active material has lithium, a transition metal, oxygen, magnesium, and fluorine, and the peak position of the binding energy of fluorine on the surface of the positive electrode active material measured by X-ray photoelectron spectroscopy is 682 eV or more and less than 685 eV, and it is a positive electrode active material. Also, in the above, the transition metal preferably contains cobalt. Or, in the above

[0018] Also, one aspect of the present invention is a positive electrode active material. The positive electrode active material has lithium, a transition metal, oxygen, magnesium, and fluorine, and the peak position of the binding energy of fluorine on the surface of the positive electrode active material measured by X-ray photoelectron spectroscopy is 682 eV or more and less than 685 eV, and it is a positive electrode active material.

[0019] Also, in the above, the transition metal preferably contains cobalt. Or, in the above , the transition metal preferably includes manganese, cobalt, and nickel.

[0020] Moreover, one aspect of the present invention is a positive electrode active material, which has a first region and a second region. The first region is inside and contains lithium, a transition metal, and oxygen, and has a layered rock salt-type crystal structure. The second region exists in the surface layer part and a part of the inside, contains magnesium, fluorine, and oxygen, and has a rock salt-type crystal structure. The crystal orientations of the first region and the second region are the same, and the ratio of the magnesium concentration to the 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). Moreover, in the above, the peak position of the binding energy of fluorine on the surface of the positive electrode active material measured by X-ray photoelectron spectroscopy is preferably 682 eV or more and less than 685 eV. Moreover, one aspect of the present invention is a method for producing a positive electrode active material, which includes a step of mixing a lithium source, a transition metal source, a magnesium source, and a fluorine source, a step of heating at 800 °C or more and 1100 °C or less for 2 hours or more and 20 hours or less, and a step of heating in an atmosphere containing oxygen at 500 °C or more and 1200 °C or less for a holding time of 50 hours or less. The atomic ratio of fluorine contained in the fluorine source to magnesium contained in the magnesium source is Mg:F = 1:x (1.5 ≤ x ≤ 4). Moreover, one aspect of the present invention is a positive electrode active material, which has a first region and a second region. The first region exists inside the positive electrode active material, and the second region exists on the surface of the positive electrode active material. The crystal orientations of the first region and the second region are the same, and the ratio of the magnesium concentration to the 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). The peak position of the binding energy of fluorine on the surface of the positive electrode active material measured by X-ray photoelectron spectroscopy is preferably 682 eV or more and less than 685 eV.

[0021] Moreover, in the above, the peak position of the binding energy of fluorine on the surface of the positive electrode active material measured by X-ray photoelectron spectroscopy is preferably 682 eV or more and less than 685 eV. Moreover, one aspect of the present invention is a method for producing a positive electrode active material, which includes a step of mixing a lithium source, a transition metal source, a magnesium source, and a fluorine source, a step of heating at 800 °C or more and 1100 °C or less for 2 hours or more and 20 hours or less, and a step of heating in an atmosphere containing oxygen at 500 °C or more and 1200 °C or less for a holding time of 50 hours or less. The atomic ratio of fluorine contained in the fluorine source to magnesium contained in the magnesium source is Mg:F = 1:x (1.5 ≤ x ≤ 4).

[0022] Moreover, one aspect of the present invention is a positive electrode active material, which has a first region and a second region. The first region exists inside the positive electrode active material, and the second region exists on the surface of the positive electrode active material. The crystal orientations of the first region and the second region are the same, and the ratio of the magnesium concentration to the 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). The peak position of the binding energy of fluorine on the surface of the positive electrode active material measured by X-ray photoelectron spectroscopy is preferably 682 eV or more and less than 685 eV. Moreover, one aspect of the present invention is a method for producing a positive electrode active material, which includes a step of mixing a lithium source, a transition metal source, a magnesium source, and a fluorine source, a step of heating at 800 °C or more and 1100 °C or less for 2 hours or more and 20 hours or less, and a step of heating in an atmosphere containing oxygen at 500 °C or more and 1200 °C or less for a holding time of 50 hours or less. The atomic ratio of fluorine contained in the fluorine source to magnesium contained in the magnesium source is Mg:F = 1:x (1.5 ≤ x ≤ 4). The atomic ratio of fluorine contained in the fluorine source to magnesium contained in the magnesium source is Mg:F = 1:x (1.5 ≤ x ≤ 4). This is a method for producing a positive electrode active material.

[0023] Moreover, one aspect of the present invention is a positive electrode active material, which has a first region and a second region. The first region exists inside the positive electrode active material, and the second region exists on the surface of the positive electrode active material. The first region exists inside the positive electrode active material, and the second region exists on the surface of the positive electrode active material. It exists in the surface part and a part of the interior, and the first region has lithium, cobalt, and oxygen. The second region has cobalt, magnesium, fluorine, and oxygen, and when the positive electrode active material is analyzed by electron energy loss spectroscopy, the L3 / L of cobalt in the first region 2 is less than 3.8, and the cobalt in the second region has L3 / L2 of 3.8 or more. It is a positive electrode active material.

Advantages of the Invention

[0024] According to one aspect of the present invention, by using it in a lithium-ion secondary battery, it is possible to provide a positive electrode active material in which a decrease in capacity during charge and discharge cycles is suppressed. In addition, it is possible to provide a secondary battery with a high capacity. Further, it is possible to provide a secondary battery having excellent charge and discharge characteristics. Moreover, it is possible to provide a secondary battery with high safety or reliability. Further, it is possible to provide a novel substance, active substance, power storage device, or a method for producing them.

Brief Description of the Drawings

[0025]

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Best Mode for Carrying Out the Invention

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that its form and details can be variously changed. Also, the present invention is not construed as being limited to the description of the embodiments shown below.

[0027] In each of the drawings described in this specification, the size, thickness, etc. of each component such as the positive electrode, negative electrode, active material layer, separator, and exterior body may be exaggerated for the sake of clarity of the individual description. Therefore, each component is not necessarily limited to its size, nor is it limited to the relative size between each component.

[0028] Also, in the configuration of the present invention described in this specification, etc., the same reference numerals are commonly used for the same part or parts having the same function among different drawings, and the repeated description thereof is omitted. Also, when referring to parts having the same function, the hatch pattern is the same, and there may be cases where no particular reference numeral is attached.

[0029] Also, Miller indices are used for the notation of crystal planes and directions. In the notation of Miller indices, in crystallography, a bar is attached above the number, but in this specification, etc., due to the restrictions of the application notation, a -(minus sign) is attached before the number. Also, the individual orientation indicating the direction within the crystal is in [], the set orientation indicating all equivalent directions is in <>, the individual plane indicating the crystal plane is in (), and the set plane having equivalent symmetry is in {} respectively.

[0030] In this specification and the like, segregation refers to a phenomenon in a solid composed of a plurality of elements (for example, A, B, C) wherein a certain element (for example, B) is unevenly distributed.

[0031] In this specification and the like, the layered rock salt-type crystal structure of a composite oxide containing lithium and a transition metal means a crystal structure having a rock salt-type ion arrangement in which cations and anions are alternately arranged, and the transition metal and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. Note that there may be defects such as cation or anion deficiencies. Also, the layered rock salt-type crystal structure is, strictly speaking, a structure in which the lattice of the rock salt-type crystal is distorted in some cases.

[0032] The rock salt-type crystal structure means a structure in which cations and anions are alternately arranged. Note that there may be cation or anion deficiencies.

[0033] The anions of the layered rock salt-type crystal and the rock salt-type crystal adopt a cubic close-packed structure (face-centered cubic lattice structure). When the layered rock salt-type crystal and the rock salt-type crystal are in contact, there is a crystal plane where the cubic close-packed structure composed of anions coincides. However, since the space group of the layered rock salt-type crystal is R-3m and is different from the space group Fm-3m of the rock salt-type, the indices of the crystal planes satisfying the above conditions are different for the layered rock salt-type crystal and the rock salt-type crystal. In this specification, for the layered rock salt-type crystal and the rock salt-type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it can be said that the crystal orientations are generally consistent.

[0034] For example, lithium cobaltate having a layered rock salt-type crystal structure and ​​​​​​​When in contact with magnesium oxide, the crystal orientations are approximately the same for lithium cobaltate when the (1-1-4) plane of lithium cobaltate contacts the {001} plane of magnesium oxide, for lithium cobaltate when the (104) plane of lithium cobaltate contacts the {001} plane of magnesium oxide, for lithium cobaltate when the (0-14) plane of lithium cobaltate contacts the {001} plane of magnesium oxide, for lithium cobaltate when the (001) plane of lithium cobaltate contacts the {111} plane of magnesium oxide, for the (012) plane of lithium cobaltate when it contacts the {111} plane of magnesium oxide, etc.

[0035] The approximate alignment of the crystal orientations in the two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc. It can also be used as a material for judgment by X-ray diffraction, electron beam diffraction, neutron beam diffraction, etc. In TEM images, etc., the arrangement of cations and anions can be observed as a repetition of bright and dark lines. When the orientations of the cubic close-packed structures in layered rock-salt type crystals and rock-salt type crystals are aligned, it can be observed that the angle formed by the repetition of bright and dark lines between crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that in some cases, light elements such as oxygen and fluorine cannot be clearly observed in TEM images, etc., but in such cases, the alignment of the metal elements can be used to judge the alignment. In this specification, etc., the similarity in the structure of the two-dimensional interface is called epitaxy. Also, crystal growth having similarity in the structure of the two-dimensional interface is called epitaxial growth. Further, having a three-dimensional structural similarity or having the same crystallographic orientation is called topotaxy

[0036] ​​​​​That is. Therefore, in the case of topotaxy, when a part of the cross-section is observed, the crystal orientations of the two regions (for example the region that serves as the base and the region formed by growth) are approximately the same.

[0037] (Embodiment 1) [Structure of the positive electrode active material] First, with reference to FIG. 1, the positive electrode active material 100, which is one aspect of the present invention, will be described. As shown in FIG. 1(A ), the positive electrode active material 100 has a first region 101 and a second region 102. It can also be said that the second region 102 is on the first region 101, or the second region 102

[0038] It may be said that the second region 102 covers at least a part of the first region 101. The first region 101 and the second region 102 are regions having different compositions. However, since the second region 102 is preferably a region where specific elements are segregated, as will be described later, the boundary between the two regions may not be clear. In FIG. 1(A), the first region 101 and the second region 102 are separated by a dotted line, and the gradient of the concentration of the elements crossing the dotted line is shown in varying shades of gray. For convenience, from FIG. 1(B) onwards, the boundary between the first region 101 and the second region 102 will be shown only by a dotted line. Details of the boundary between the first region 101 and the second region 102 will be described later.

[0039] Also, as shown in FIG. 1(B), the second region 102 may be present inside the positive electrode active material. For example, when the first region 101 is polycrystalline, specific elements may segregate at grain boundaries and in their vicinity, forming the second region 102. Also, specific elements may segregate at and in the vicinity of the crystal defect portions of the positive electrode active material, forming the second region 102. Note that this In the specification and the like, a crystal defect refers to a defect observable in a TEM image or the like, or a structure in which other elements are incorporated into the crystal. and so on.

[0040] Also, as shown in FIG. 1(B), the second region 102 does not have to cover all of the first region 101. That is, the first region 101 exists inside the positive electrode active material 100, and the second region 102 exists in the surface layer portion of the positive electrode active material 100. Further, the second region 102 may exist inside the positive electrode active material 100.

[0041] In other words, the first region 101 exists inside the positive electrode active material 100, and the second region 102 exists in the surface layer portion of the positive electrode active material 100. Further, the second region 102 may exist inside the positive electrode active material 100. 2 exists in the surface layer portion of the positive electrode active material 100. Further, the second region 102 may exist inside the positive electrode active material 100. 00.

[0042] Also, the first region 101 may be referred to as, for example, solid phase A. Also, the second region 102 may be referred to as, for example, solid phase B. and so on.

[0043] If the particle size of the positive electrode active material 100 is too large, it becomes difficult for lithium to diffuse, and when coated on the current collector, the surface of the active material layer becomes too rough, etc. On the other hand, if it is too small, it becomes difficult to support the active material layer during coating on the current collector, and problems such as excessive progress of the reaction with the electrolyte also occur. Therefore, it is preferable that the D50 (also referred to as the median diameter) is 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 40 μm or less. and so on. When coating on the current collector, it becomes difficult to support the active material layer, and problems such as excessive progress of the reaction with the electrolyte also occur. Therefore, it is preferable that the D50 (also referred to as the median diameter) is 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 40 μm or less. occurs. Therefore, it is preferable that the D50 (also referred to as the median diameter) is 0.1 μm or more and 100 μm or less, and more preferably 1 μm or more and 40 μm or less. is more preferably 1 μm or more and 40 μm or less.

[0044] <First Region 101> The first region 101 contains lithium, a transition metal, and oxygen. The first region 101 may be said to have a composite oxide containing lithium and a transition metal. and so on.

[0045] 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, among manganese, cobalt, and nickel, and so on. One or more of them can be used. That is, the transition metal possessed by the first region 101 and only cobalt may be used, or two types of cobalt and manganese may be used, or three types of cobalt, manganese, and nickel may be used. Further, in addition to the transition metal, the first region 101 may have a metal other than the transition metal such as aluminum.

[0046] That is, the first region 101 can have a composite oxide containing lithium and a transition metal, such as lithium cobaltate, lithium nickelate, lithium cobaltate in which a part of cobalt is replaced by manganese, lithium nickel-manganese-cobaltate, lithium nickel-cobalt-aluminate, etc.

[0047] The first region 101 functions as a region that particularly contributes to the charge-discharge reaction among the positive electrode active materials 100. In order to increase the capacity when the positive electrode active material 100 is used in a secondary battery, it is preferable

[0048] that the first region 101 has a larger volume than the second region 102. A layered rock salt-type crystal structure is preferable as the first region 101 because lithium can diffuse two-dimensionally easily. Further, when the first region 101 has a layered rock salt-type crystal structure, unexpectedly, magnesium tends to segregate as described later. However, not all of the first region 101 needs to have a layered rock salt- type crystal structure. For example, there may be crystal defects in a part of the first

[0049] <The second region 102> The second region 102 contains magnesium, fluorine, and oxygen. For example, it can be said that the second region 102 contains magnesium oxide and part of the oxygen is substituted by fluorine.

[0050] The second region 102 covers at least a part of the first region 101. Since the magnesium oxide contained in the second region 102 is an electrochemically stable material, it is suitable as a coating layer because deterioration hardly occurs even when charge and discharge are repeated.

[0051] If the second region 102 is too thin, its function as a coating layer will deteriorate, but if it is too thick, it will cause a decrease in capacity. Therefore, the thickness of the second region is preferably 0.5 nm or more and 50 nm or less, and more preferably 0.5 nm or more and 3 nm or less.

[0052] If the second region 102 has a rock-salt type crystal structure, it is preferable because the crystal orientation is likely to be consistent with that of the first region 101 and it is likely to function as a stable coating layer. However, not all of the second region 102 needs to have a rock-salt type crystal structure. For example, a part of the second region 102 may be amorphous or may have another crystal structure.

[0053] Generally, as the cathode active material repeats charge and discharge, side reactions such as transition metals such as cobalt and manganese eluting into the electrolyte, oxygen detaching, and the crystal structure becoming unstable occur, and deterioration progresses. However, since the cathode active material 100 according to one aspect of the present invention has the second region 102 in the surface layer portion, it is possible to make the crystal structure of the composite oxide containing lithium and transition metals contained in the first region 101 more stable.

[0054] ​​​​​​​​​​Further, the second region 102 has magnesium, fluorine, and oxygen, and preferably further has the same transition metal as that of the first region 101. When the first region 101 and the second region 102 have the same transition metal, it is preferable that the valence of the transition metal is different in these two regions. More specifically, it is preferable that the transition metal in the first region 101 has more trivalent atoms than atoms of other valences, and it is preferable that the transition metal in the second region 102 has more divalent atoms than atoms of other valences.

[0055] When there are many divalent transition metals in the second region 102, many metal oxides with a transition metal:oxygen = 1:1 (atomic ratio), such as CoO(II), MnO(II), and Ni( (II), increase. These metal oxides easily form a stable solid solution with magnesium oxide, which is also an oxide of a divalent metal. Therefore, the second region 102 can become a more stable and better coating layer.

[0056] The valence of the transition metal can be analyzed by EELS (electron energy loss spectroscopy), XAFS (X-ray absorption fine structure analysis), XPS (X-ray photoelectron spectroscopy), ESR (electron spin resonance), Mössbauer spectroscopy, etc. Among them, since EELS has a high spatial resolution, it can analyze even if the second region 102 is a thin layer of several nm, which is preferable.

[0057] When analyzing the valence of the transition metal by EELS, the valence can be determined by the ratio of L3 / L2. The higher the L3 / L2, the higher the proportion of the divalent transition metal. For example, when analyzing the transition metals in the first region 101 and the second region 102 by EELS, the L3 / L2 of the transition metal in the first region 101 is less than 3.8, and the transition metal in the second region 102 has L3 When analyzing the transition metals in the first region 101 and the second region 102 by EELS, the L3 / L2 of the transition metal in the first region 101 is less than 3.8, and the transition metal in the second region 102 has L3 of the transition metal in the first region 101 is less than 3.8, and the L3 / L2 of the transition metal in the second region 102 is / L2 is preferably 3.8 or more.

[0058] In addition, the second region 102 may also contain lithium.

[0059] Also, as shown in Fig. 1(B), when the second region 102 also exists inside the first region 101 , it may be preferable because the crystal structure of the composite oxide containing lithium and the transition metal in the first region 101 can be further stabilized.

[0060] In addition, the fluorine in the second region 102 preferably exists in a bonding state other than MgF2 and LiF. Specifically, when the surface of the positive electrode active material 100 is analyzed by XPS, the peak position of the binding energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, more preferably about 684.3 eV. This is a binding energy that does not match either of MgF2 and LiF.

[0061] In this specification etc., the peak position of the binding energy of a certain element when analyzed by XPS refers to the value of the binding energy at which the intensity of the energy spectrum is maximized within the range corresponding to the binding energy of that element.

[0062] <Boundary between the first region 101 and the second region 102> The first region 101 and the second region 102 can be confirmed to have different compositions by TEM images, STEM images, FFT (Fast Fourier Transform) analysis, EDX (Energy Dispersive X-ray Analysis), depth-direction analysis by ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), XPS (X-ray Photoelectron Spectroscopy), Auger electron spectroscopy, TDS (Temperature Programmed Desorption Gas Analysis), etc. For example, in the cross-sectional TEM image and STEM image of the positive electrode active material 100, the difference in the constituent elements is observed as the difference in the brightness of the image, so it can be observed that the constituent elements of the first region 101 and the second region 102 are different. Also, in the elemental distribution image of EDX, it can be observed that the first region 101 and the second region 102 have different elements. However, it is not always necessary to be able to observe a clear boundary between the first region 101 and the second region 102 by various analyses.

[0063] In this specification and the like, the range of the second region 102 present in the surface layer portion of the positive electrode active material 100 refers to the range from the outermost surface of the positive electrode active material 100 to the depth at which the concentration of magnesium detected by depth direction analysis becomes 1 / 5 of the peak. As the depth direction analysis, the above-mentioned line analysis of EDX, and depth direction analysis using ToF-SIMS and the like can be used. The peak of the magnesium concentration preferably exists up to a depth of 2 nm from the surface of the positive electrode active material 100 toward the center, more preferably up to a depth of 1 nm, and even more preferably up to a depth of 0.5 nm. The depth at which the magnesium concentration becomes 1 / 5 of the peak, that is, the range of the second region 102, varies depending on the manufacturing method, but in the case of the manufacturing method described later, it is generally from 2 nm or more to about 5 nm from the surface of the positive electrode active material.

[0064] Regarding the second region 102 existing inside the first region 101, it also refers to a region where the concentration of magnesium detected by depth direction analysis is 1 / 5 or more of the peak.

[0065] The distribution of fluorine in the positive electrode active material 100 preferably overlaps with the distribution of magnesium. Therefore, the peak of the fluorine concentration is from the surface of the positive electrode active material 100 toward the center. ​​​​​​​​​​​​​​ It is preferably present up to 2 nm, more preferably present up to 1 nm in depth, and even more preferably present up to 0.5 nm in depth.

[0066] Thus, it can be said that the second region 102 is a concentration gradient region where the concentrations of magnesium and fluorine decrease from the surface of the positive electrode active material 100 toward the inside.

[0067] The concentrations of magnesium and fluorine can be analyzed by ToF-SIMS, XPS, Auger electron spectroscopy, TDS, etc.

[0068] Note that the measurement range of XPS is about 5 nm from the surface of the positive electrode active material 100. Therefore, the elemental concentration existing about 5 nm from the surface can be quantitatively analyzed. Therefore, when the thickness of the second region 10 2 is less than 5 nm, the region combining the second region 102 and a part of the first region 101, when the thickness of the second region 102 is 5 nm or more from the surface, the elemental concentration of the second region 102 can be quantitatively analyzed. By performing XPS analysis on the surface of the positive electrode active material 100, when the total amount of atoms including lithium, transition metals, oxygen, fluorine, and magnesium contained in the first region 101 is 100 atomic%, the magnesium concentration is 1 atomic% or more and 16 atomic% or less, and the fluorine concentration is 0.2 atomic% or more and 4 atomic % or less. Also, the ratio of the concentrations of magnesium and fluorine is preferably Mg:F = y: 1 (3 ≤ y ≤ 5) (atomic ratio), and more preferably about Mg:F = 4:1. When the magnesium concentration and the fluorine concentration are within these ranges, the positive electrode active material 100 can exhibit extremely good cycle characteristics when used in a secondary battery.

[0069] As described above, the concentrations of magnesium and fluorine gradually decrease from the surface toward the interior, so the first region 101 may have elements that the second region 102 such as magnesium has. Similarly, the second region 102 may have elements that the first region 101 has. Also, the first region 101 may have other elements such as carbon, sulfur, silicon, sodium, calcium, chlorine, zirconium, etc. The second region 102 may have other elements such as carbon, sulfur, silicon, sodium, calcium, chlorine, zirconium, etc.

[0070] [Segregation] The second region 102 can also be formed by methods such as sputtering, solid-phase method, liquid-phase methods including sol-gel method, etc. However, the inventors of the present invention have clarified that after mixing a magnesium source and a fluorine source as starting materials and heating, magnesium can be segregated to form the second region 102. Furthermore, it has been clarified that the positive electrode active material having the second region 102 formed in this way has extremely excellent characteristics.

[0071] For example, in Example 4 of Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2016-076454), after synthesizing a composite oxide containing magnesium, the powder of the composite oxide and lithium fluoride are mixed and heated to form a surface oxide fluorinated and lithiated on the surface of the composite oxide. It is described that magnesium was not detected from the surface oxide by this method.

[0072] However, the inventors of the present invention simultaneously mix a magnesium source and a fluorine source as starting materials, ​​​​​​​​​As a result, magnesium oxide could be segregated to the surface layer of the positive electrode active material 100. Intention Surprisingly, the inventors have revealed that fluorine added to the starting materials has the effect of segregating magnesium. Inventors have revealed.

[0073] In order to form the second region 102 by segregation of magnesium, magnesium can be segregated not only to the surface layer of the positive electrode active material 100 but also to grain boundaries and their vicinity, crystal defects and their vicinity. The second region 102 formed in grain boundaries and their vicinity and crystal defects and their vicinity can contribute to further stabilization of the crystal structure of the composite oxide containing lithium and transition metal that the first region 101 has. The second region 102 formed in grain boundaries and their vicinity and crystal defects and their vicinity can contribute to further stabilization of the crystal structure of the composite oxide containing lithium and transition metal that the first region 101 has. The second region 102 formed in grain boundaries and their vicinity and crystal defects and their vicinity can contribute to further stabilization of the crystal structure of the composite oxide containing lithium and transition metal that the first region 101 has. The second region 102 formed in grain boundaries and their vicinity and crystal defects and their vicinity can contribute to further stabilization of the crystal structure of the composite oxide containing lithium and transition metal that the first region 101 has.

[0074] In order to effectively perform the segregation of the second region 102, the concentrations of magnesium and fluorine in the raw materials are preferably Mg:F = 1:x (1.5 ≤ x ≤ 4) (atomic ratio), and more preferably about Mg:F = 1:2 :F = 1:x (1.5 ≤ x ≤ 4) (atomic ratio), and more preferably about Mg:F = 1:2 (atomic ratio).

[0075] On the other hand, the concentrations of magnesium and fluorine in the second region 102 formed as a result of segregation are preferably Mg:F = y:1 (3 ≤ y ≤ 5) (atomic ratio), and more preferably about Mg:F = 4:1 g:F = y:1 (3 ≤ y ≤ 5) (atomic ratio), and more preferably about Mg:F = 4:1 (atomic ratio).

[0076] Since the second region 102 formed by segregation is formed by epitaxial growth, the crystal orientations of the first region 101 and the second region 102 may be generally in agreement in part. That is, the first region 101 and the second region 102 may be topotactic. When the crystal orientations of the first region 101 and the second region 102 are generally in agreement, the second region 102 can function as a better coating layer. Since the second region 102 formed by segregation is formed by epitaxial growth, the crystal orientations of the first region 101 and the second region 102 may be generally in agreement in part. That is, the first region 101 and the second region 102 may be topotactic. When the crystal orientations of the first region 101 and the second region 102 are generally in agreement, the second region 102 can function as a better coating layer. That is, the first region 101 and the second region 102 may be topotactic. When the crystal orientations of the first region 101 and the second region 102 are generally in agreement, the second region 102 can function as a better coating layer. When the crystal orientations of the first region 101 and the second region 102 are generally in agreement, the second region 102 can function as a better coating layer. When the crystal orientations of the first region 101 and the second region 102 are generally in agreement, the second region 102 can function as a better coating layer.

[0077] <Third region 103> So far, an example in which the positive electrode active material 100 has the first region 101 and the second region 102 has been described. However, one aspect of the present invention is not limited to this. For example, as shown in FIG. 1(C), the positive electrode active material 100 may have a third region 103. The third region 103 can be provided, for example, so as to be in contact with at least a part of the second region 102. The third region 103 may be a film having carbon such as a graphene compound, or may be a film having lithium or a decomposition product of the electrolytic solution. When the third region 103 is a film having carbon, the conductivity between the positive electrode active materials 100 and between the positive electrode active material 100 and the current collector can be enhanced. Also, when the third region 103 is a film having lithium or a decomposition product of the electrolytic solution, an excessive reaction with the electrolytic solution can be suppressed, and the cycle characteristics can be improved when used in a secondary battery.

[0078] Furthermore, a buffer region may be provided between the first region 101 and the second region 102. The buffer region preferably has metals such as titanium, aluminum, zirconium, and vanadium in addition to lithium, transition metals, and oxygen. The buffer region may overlap with the first region 101 and the second region 102. When the positive electrode active material 100 has a buffer region, the crystal structures of the first region 101 and the second region 102 can be further stabilized, and a positive electrode active material with even better cycle characteristics can be obtained, which is preferable.

[0079] [Production method] Having the first region 101 and the second region 102, and forming the second region 102 by segregation The method for producing the positive electrode active material 100 in the case will be described with reference to FIG. 2. In the present embodiment, when the transition metal included in the first region 101 is cobalt, that is, when the first region 101 has lithium cobaltate, it will be described. Further, the case of forming the second region 102 having magnesium oxide and fluorine by segregation will be described.

[0080] First, starting materials are prepared (S11). Specifically, a lithium source, a cobalt source, a magnesium source, and a fluorine source are each weighed. As the lithium source, for example, lithium carbonate, lithium fluoride, lithium hydroxide, or the like can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, cobalt oxyhydroxide, cobalt carbonate, cobalt oxalate, cobalt sulfate, or the like can be used. As the magnesium source, for example, magnesium oxide, magnesium fluoride, or the like can be used. As the fluorine source, for example, lithium fluoride, magnesium fluoride, or the like can be used. That is, lithium fluoride can be used as both the lithium source and the fluorine source, and magnesium fluoride can be used as both the magnesium source and the fluorine source.

[0081] In the present 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 the lithium source and the fluorine source.

[0082] The atomic ratio of magnesium to fluorine in the raw materials is preferably Mg:F = 1:x (1.5 ≦ x ≦ 4) (atomic ratio), and more preferably about Mg:F = 1:2 (atomic ratio) because The ratio of magnesium oxide to lithium fluoride is preferably MgO:LiF = 1:x (1.5 ≤ x ≤ 4) ( molar ratio), and more preferably about MgO:LiF = 1:2 (molar ratio).

[0083] The molar ratio of each raw material can be, for example, as follows. 1 / 2·Li2CO3 + ((1 - z) / 3)·Co3O4 + z·MgO + 2z·LiF (z = 0.01)

[0084] Next, the weighed starting materials are mixed (S12). For mixing, for example, a ball mill, a bead mill, etc. can be used.

[0085] Next, the material mixed in S12 is heated (S13). This step may be referred to as the first heating or firing for the purpose of distinction from the subsequent heating step. The first heating is preferably performed at 800°C or higher and 1050°C or lower, and more preferably at 900°C or higher and 1000°C or lower. The heating time is preferably 2 hours or more and 20 hours or less. The first heating is preferably performed in a dried atmosphere such as dry air. The dried atmosphere preferably has a dew point of -50°C or lower, and more preferably -100°C or lower. In this embodiment, heating is performed at 1000°C for 10 hours, the temperature is raised at 200°C / h, and dry air with a dew point of -109°C is flowed at 10 L / min. By the first heating in S13, a composite oxide containing lithium and a transition metal in the first region 101 can be synthesized. Also, by this first heating, a part of the magnesium and fluorine contained in the starting materials segregates to the surface layer portion of the composite oxide containing lithium and a transition metal. However

[0086] ​​​​​​​​​​At this point, most of the magnesium and fluorine are in a state of being dissolved in the composite oxide containing lithium and transition metals. It is in a solid solution state.

[0087] Next, the material heated in S13 is cooled to room temperature (S14). The cooling is preferably carried out over the same or more time as the heating up. For example, it can be carried out over a time of 10 hours or more and 15 hours or less. After cooling, it is preferable to sieve the synthesized material. In this embodiment, it is sieved using a 53 μm mesh. It is preferable to sieve the synthesized material. In this embodiment, it is sieved using a 53 μm mesh. In this embodiment, it is sieved using a 53 μm mesh.

[0088] In addition, particles of a composite oxide containing lithium, cobalt, fluorine, and magnesium synthesized in advance as starting materials may be used. In this case, steps S12 to S14 can be omitted. can be omitted.

[0089] Next, a second heating is performed on the material cooled in S14 (S15). This step may be referred to as the second heating or annealing for the purpose of distinguishing it from the previous heating step. 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, etc., but it is preferable to carry out the holding time at a specified temperature for 50 hours or less, and 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 about 800 °C It is also preferable to heat in an atmosphere containing oxygen. In this embodiment, it is heated at 800 °C for 2 hours, the temperature increase is 200 °C / h, and dry air with a dew point of -109 °C is passed at 10 L / min. for 2 hours, the temperature increase is 200 °C / h, and dry air with a dew point of -109 °C is passed at 10 L / min.

[0090] By performing the second heating in S15, it is possible to promote the segregation of magnesium and fluorine contained in the starting materials to the surface layer of the composite oxide containing lithium, manganese, and transition metals.

[0091] Finally, the material heated in S15 is cooled to room temperature. The cooling is preferably performed over the same or a longer time as the heating. Then, the cooled material is recovered (S16), and the positive electrode active material 100 having the first region 101 and the second region 102 can be obtained. By using the positive electrode active material described in this embodiment, a secondary battery with high capacity and good cycle characteristics can be obtained. This embodiment can be used in appropriate combination with other embodiments.

[0092]

[0093] (Embodiment 2) In this embodiment, examples of other materials that can be used in the secondary battery having the positive electrode active material 100 described in the previous embodiment will be described. In this embodiment, a secondary battery in which the positive electrode, negative electrode, and electrolyte are wrapped in an outer package will be described as an example.

[0094] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector.

[0095] [Positive Electrode Active Material Layer] The positive electrode active material layer has a positive electrode active material. Further, the positive electrode active material layer may have a conductive auxiliary agent and a binder.

[0096] As the positive electrode active material, the positive electrode active material 100 described in the previous embodiment can be used. By using the positive electrode active material 100 described in the previous embodiment, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0097] ​​​​​​​​​ As the conductive assistant, a carbon material, a metal material, a conductive ceramic material, or the like can be used. Also, a fibrous material may be used as the conductive assistant. The content of the conductive assistant with respect to the total amount of the active material layer is preferably 1 wt% or more and 10 wt% or less, and more preferably 1 wt% or more and 5 wt% or less.

[0098] The conductive assistant can form an electrical conduction network in the electrode. By the conductive assistant, the electrical conduction path between the positive electrode active materials can be maintained. By adding the conductive assistant to the active material layer, an active material layer having high electrical conductivity can be realized.

[0099] As the conductive assistant, for example, natural graphite, artificial graphite such as mesocarbon microbeads, carbon fibers, etc. can be used. As the carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. Also, as the carbon fibers, carbon nanofibers, carbon nanotubes, etc. can be used. Carbon nanotubes can be produced, for example, by a vapor growth method. Also, as the conductive assistant, for example, carbon materials such as carbon black (acetylene black (AB), etc.), graphite (black lead) particles, graphene, fullerenes, etc. can be used. Also, for example, metal powders, metal fibers, conductive ceramic materials, etc. such as copper, nickel, aluminum, silver, gold, etc. can be used.

[0100] Also, a graphene compound may be used as the conductive assistant.

[0101] The graphene compound has excellent electrical properties of having high electrical conductivity, high flexibility and high It may have excellent physical properties such as mechanical strength. Also, graphene compounds have a planar shape. Graphene compounds enable surface contact with low contact resistance. Also, even when thin, it may have very high conductivity and can efficiently form conductive paths within the active material layer in a small amount. Therefore, using a graphene compound as a conductive aid is preferable because it can increase the contact area between the active material and the conductive aid. Also it is preferable because it may be able to reduce electrical resistance. Here, as an example of the graphene compound for example, it is particularly preferable to use graphene or multi - graphene or reduced Graphene O xide (hereinafter, RGO). Here, RGO refers to a compound obtained by reducing, for example, graphene oxide (GO).

[0102] When using an active material with a small particle size, for example, an active material of 1 μm or less, the specific surface area of the active material is large, and more conductive paths connecting the active materials are required. Therefore, the amount of the conductive aid tends to be large and the loading amount of the active material relatively decreases. When the loading amount of the active material decreases, the capacity of the secondary battery decreases. In such a case, when using a graphene compound as the conductive aid the graphene compound can efficiently form conductive paths even in a small amount so that it is not necessary to reduce the loading amount of the active material, which is particularly preferable.

[0103] Hereinafter, as an example, a cross - sectional configuration example of using a graphene compound as a conductive aid in the active material layer 200 will be described.

[0104] Fig. 3(A) shows a longitudinal sectional view of the active material layer 200. The active material layer 200 is a granular positive electrode active material It includes 100, a graphene compound 201 as a conductive assistant, and a binder (not shown). Here, for example, graphene or multi - graphene may be used as the graphene compound 201. Here, the graphene compound 201 preferably has a sheet - like shape. Also, the graphene compound 201 may be formed by a plurality of multi - graphenes and / or a plurality of graphenes partially overlapping to form a sheet - like shape.

[0105] In the longitudinal section of the active material layer 200, as shown in FIG. 3(A), the sheet - like graphene compound 201 is dispersed substantially uniformly inside the active material layer 200. In FIG. 3(A), the graphene compound 201 is schematically represented by a thick line, but actually it is a thin film having a thickness of a single layer or multiple layers of carbon molecules. A plurality of graphene compounds 201 are formed so as to wrap, cover, or adhere onto the surfaces of a plurality of granular positive - electrode active materials 100, so they are in surface contact with each other.

[0106] Here, when a plurality of graphene compounds bond to each other, a network - like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed. When the active material is covered by the graphene net, the graphene net can also function as a binder that binds the active materials to each other. Therefore, the amount of the binder can be reduced or the binder can be not used, so that the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the capacity of the energy storage device can be increased.

[0107] Here, graphene oxide is used as the graphene compound 201 and mixed with the active material to form the active material​​​​​​ After forming the layer to be layer 200, it is preferably reduced. In the formation of the graphene compound 201 , by using graphene oxide with extremely high dispersibility in a polar solvent, graphene compound 201 can be dispersed substantially uniformly inside the active material layer 200. Uniformly remove the solvent by volatilization from the dispersion medium containing uniformly dispersed graphene oxide, and reduce the graphene oxide Therefore, the graphene compounds 201 remaining in the active material layer 200 partially overlap each other and are dispersed to the extent of surface contact with each other, so that a three-dimensional conductive path can be formed. Note that the reduction of graphene oxide may be performed, for example, by heat treatment or by using a reducing agent.

[0108] Therefore, unlike granular conductive aids such as acetylene black that make point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance. Therefore, it can improve the electrical conductivity between the granular positive electrode active material 100 and the graphene compound 201 with a smaller amount than ordinary conductive aids. Therefore, the ratio in the active material layer 200 of the positive electrode active material 100 can be increased. Thereby, the discharge capacity of the power storage device can be increased.

[0109] As the binder, for example, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene -styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Also as the binder , fluororubber can be used.

[0110] Also, as the binder, for example, it is preferable to use a water-soluble polymer. Water-soluble polymers As the child, for example, polysaccharides or the like can be used. As the polysaccharide, carboxymethyl cellulose (CMC), methylcellulose, ethylcellulose, hydroxypropyl cellulose, cellulose derivatives such as diacetyl cellulose, regenerated cellulose, starch, etc. can be used. Further, it is more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0111] Alternatively, as the binder, polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate (PMMA)), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene lene, isobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose and other materials are preferably used.

[0112] The binder may be used in combination of a plurality of the above.

[0113] For example, a material having a particularly excellent viscosity adjustment effect may be used in combination with other materials. For example, rubber materials and the like are excellent in adhesive force and elastic force, but may be difficult to adjust the viscosity when mixed with a solvent. In such a case, for example, it is preferable to mix with a material having a particularly excellent viscosity adjustment effect. As the material having a particularly excellent viscosity adjustment effect, for example, a water-soluble polymer may be used. Further, as the water-soluble polymer having a particularly excellent viscosity adjustment effect, the above-mentioned polysaccharides, for example, cal ​Boxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxy propyl cellulose and cellulose derivatives such as diacetyl cellulose, regenerated cellulose, etc., or starch can be used.

[0114] In addition, cellulose derivatives such as carboxymethyl cellulose can be made into salts such as sodium salts and ammonium salts of carboxymethyl cellulose, which increases solubility and makes it easier to exhibit the effect as a viscosity modifier. By increasing solubility, the dispersion of the active material and other components can also be enhanced when preparing the electrode slurry. In this specification, cellulose and cellulose derivatives used as electrode binders shall include those salts.

[0115] Water-soluble polymers stabilize the viscosity by dissolving in water, and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, etc. in an aqueous solution. Also, due to having functional groups, they are expected to be easily and stably adsorbed on the surface of the active material. Also, cellulose derivatives such as carboxymethyl cellulose, for example, have many materials with functional groups such as hydroxyl groups and carboxyl groups. Due to having functional groups, it is expected that the polymers interact with each other and widely cover the surface of the active material.

[0116] When the binder covering the surface of the active material or in contact with the surface forms a film, it is expected to serve as a passive film and suppress the decomposition of the electrolyte. Here, the passive film is a film without electron conductivity or a film with extremely low electrical conductivity. For example, on the surface of the active material ​​​​​​​​​​When a dynamic film is formed, it is possible to suppress the decomposition of the electrolyte at the battery reaction potential. In addition, the passive film preferably suppresses the electrical conductivity while allowing lithium ions to conduct. Furthermore, it is more desirable.

[0117] <Positive current collector> As the positive current collector, materials with high conductivity such as metals like stainless steel, gold, platinum, aluminum, titanium, and their alloys can be used. Also, the material used for the positive current collector preferably does not dissolve at the potential of the positive electrode. Additionally, an aluminum alloy added with elements such as silicon, titanium, neodymium, scandium, and molybdenum to improve heat resistance can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as foil, plate (sheet), net, punched metal, expanded metal, etc. The current collector is preferably one with a thickness of 5 μm or more and 30 μm or less.

[0118] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. Also, the negative electrode active material layer may have a conductive assistant and a binder.

[0119] <Negative electrode active material> As the negative electrode active material, for example, alloy-based materials, carbon-based materials, etc. can be used.

[0120] As the negative electrode active material, it is possible to perform charge and discharge reactions through alloying and dealloying reactions with lithium. Capable elements can be used. For example, at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger capacity compared to carbon. In particular, silicon has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. exist. Here, elements capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium, and compounds containing such elements, etc. may be referred to as alloy-based materials in some cases. At least one of the materials containing them can be used. Such elements have a larger capacity compared to carbon. Especially, silicon has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3 Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. exist. Here, elements capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium, and compounds containing such elements, etc. may be referred to as alloy-based materials in some cases.

[0121] In this specification, etc., SiO refers to, for example, silicon monoxide. Alternatively, SiO can also be expressed as SiO x . Here, x preferably has a value near 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less. x

[0122] As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.

[0123] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. ​​​​​​​ This is possible. Here, spherical graphite having a spherical shape can be used as artificial graphite. For example, MCMB may have a spherical shape, which is preferable. Also, it is relatively easy to reduce the surface area of MCMB, and this may be preferable. Examples of natural graphite include scaly graphite, spheroidized natural graphite, and the like.

[0124] Graphite exhibits a potential as low as that of lithium metal when lithium ions are inserted into the graphite (when forming a lithium-graphite intercalation compound) (0.05 V or more and 0.3 V or less vs. Li / L i ). As a result, a lithium-ion secondary battery can exhibit a high operating voltage. Furthermore, + graphite has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to lithium metal, and thus is preferable.

[0125] Also, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4T i5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5) , tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0126] Also, as the negative electrode active material, Li3N-type structured Li Li 3-x M x N (M = Co, Ni, Cu), which is a complex nitride of lithium and a transition metal, can be used. For example, Li 2.6 Co 0.4 N3 exhibits a large charge-discharge capacity (900 mAh / g, 1890 mAh / cm 3 ), and is preferable.

[0127] ​ When using a complex nitride of lithium and a transition metal, since the negative electrode active material contains lithium ions, it can be combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material, which is preferable. Even when using a material containing lithium ions as the positive electrode active material, by previously desorbing the lithium ions contained in the positive electrode active material, a complex nitride of lithium and a transition metal can be used as the negative electrode active material.

[0128] In addition, a material in which a conversion reaction occurs can also be used as the negative electrode active material. For example, transition metal oxides such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), which do not form an alloy with lithium, can be used as the negative electrode active material. As materials in which a conversion reaction occurs, further, oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, sulfides such as CoS, 0.89 NiS, and CuS, nitrides such as Zn3N2, Cu3N, and Ge3 N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3 also cause it.

[0129] As the conductive aid and binder that the negative electrode active material layer can have, the same materials as those that the positive electrode active material layer can have can be used.

[0130] <Negative electrode current collector> For the negative electrode current collector, the same materials as those for the positive electrode current collector can be used. It should be noted that it is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0131] [Electrolyte solution] The electrolyte solution has a solvent and an electrolyte. As the solvent of the electrolyte solution, an aprotic organic solvent is preferable. and, for example, ethylene carbonate (EC), propylene carbonate (PC), butyl ene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrola ctone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate propyl, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1 ,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide xide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tet rahydrofuran, sulfolane, sultone, etc., can be used singly or in any combination and ratio of two or more of these.

[0132] In addition, by using a polymer material that is gelled as a solvent for the electrolyte, safety against liquid leakage and the like is enhanced. Also, thinning and weight reduction of the secondary battery are possible. Representative examples of the gelled polymer material include silicone gel, acrylic gel, acrylonitrile gel, poly ylene oxide-based gel, polypropylene oxide-based gel, gel of fluorine-based polymer, etc.

[0133] In addition, by using one or more ionic liquids (room temperature molten salts) that are flame retardant and hardly volatile as the solvent for the electrolyte, even if the internal temperature rises due to internal short circuit, overcharge, etc. of the power storage device, rupture and ignition of the power storage device can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. As the organic cation used in the electrolyte, quaternary Ammonium cations, tertiary sulfonium cations, quaternary phosphonium cations, etc. include aliphatic onium cations such as , and aromatic cations such as imidazolium cations and pyridinium cations. In addition, as anions used in the electrolyte, monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions, etc. are included.

[0134] In addition, as electrolytes dissolved in the above solvents, for example, LiPF6, LiClO4, Li AsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4 , Li2B 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO 3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2) 2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. of lithium salts can be used alone or in any combination and ratio of two or more of these. It is possible.

[0135] For the electrolyte used in the power storage device, it is preferable to use a highly purified electrolyte with a low content of particulate dust and elements other than the constituent elements of the electrolyte (hereinafter, simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less. Preferably, the weight ratio of impurities to the electrolyte is 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less. Specifically, it is preferable to make the weight ratio of impurities to the electrolyte 1% or less, preferably 0.1% or less, and more preferably 0.01% or less. Preferably, it is 0.01% or less.

[0136] In addition, vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), LiBOB, and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolytic solution. The concentration of the added material may be, for example, 0.1 wt% or more and 5 wt% or less based on the entire solvent.

[0137] Alternatively, a polymer gel electrolyte obtained by swelling a polymer with an electrolytic solution may be used. By using a polymer gel electrolyte, the safety against leakage and the like is enhanced. In addition, the secondary battery can be made thinner and lighter.

[0138] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, fluorine-based polymer gel, etc. can be used.

[0139] As the polymer, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. In addition, the formed polymer may have a porous shape.

[0140] Alternatively, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide-based or oxide-based material, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide)-based material can be used. When using a solid electrolyte, the installation of a separator and a spacer becomes unnecessary. Also, the electric ​​​​​​​Since the entire battery can be solidified, the risk of liquid leakage is eliminated and the safety is significantly improved.

[0141] [Separator] Moreover, the secondary battery preferably has a separator. Examples of the separator include fibers having cellulose such as paper and non-woven fabrics, glass fibers, ceramics, or synthetic fibers made of nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into a bag shape and arranged to wrap either the positive electrode or the negative electrode.

[0142] The separator may have a multilayer structure. For example, a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof can be coated on an organic material film such as polypropylene or polyethylene. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0143] Coating with a ceramic-based material improves the oxidation resistance, so it is possible to suppress the deterioration of the separator during high-voltage charge and discharge and improve the reliability of the secondary battery. Also, coating with a fluorine-based material makes it easier for the separator and the electrode to adhere, and it is possible to improve the output characteristics. Coating with a polyamide-based material, especially aramid, improves the heat resistance, so the safety of the secondary battery ​​​​​​​​​​​The safety can be improved.

[0144] For example, a mixed material of aluminum oxide and aramid may be coated on both sides of a polypropylene film. Also, a mixed material of aluminum oxide and aramid may be coated on the surface of the polypropylene film that contacts the positive electrode, and a fluorine-based material may be coated on the surface that contacts the negative electrode.

[0145] When using a separator with a multilayer structure, even if the overall thickness of the separator is thin, the safety of the secondary battery can be maintained, so the capacity per unit volume of the secondary battery can be increased.

[0146] (Embodiment 3) In this embodiment, an example of the shape of the secondary battery having the positive electrode active material 100 described in the previous embodiment will be described. The materials used in the secondary battery described in this embodiment can refer to the description of the previous embodiment.

[0147] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. Fig. 4(A) is an external view of a coin-type (single-layer flat type) secondary battery, and Fig. 4(B) is a cross-sectional view thereof.

[0148] The coin-type secondary battery 300 has a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal, which are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. Also, the negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

[0149] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, the active material layers may be formed on only one side.

[0150] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel etc.) that are corrosion-resistant to the electrolytic solution can be used. Also, in order to prevent corrosion by the electrolytic solution, it is preferable to coat with nickel, aluminum, etc. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307 respectively.

[0151] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with the electrolyte, and as shown in Fig. 4(B), with the positive electrode can 301 facing downwards, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped via the gasket 303 to manufacture the coin-type secondary battery 300.

[0152] By using the positive electrode active material described in the previous embodiment for the positive electrode 304, a coin-type secondary battery 300 with high capacity and excellent cycle characteristics can be obtained.

[0153] [Cylindrical secondary battery] Next, an example of a cylindrical secondary battery will be described with reference to Fig. 5. As shown in Fig. 5(A), the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0154] FIG. 5(B) is a diagram schematically showing a cross section of a cylindrical secondary battery. Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. The battery can 602 has one end closed and the other end open. For the battery can 602, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys of these or alloys of these with other metals (for example, stainless steel, etc.) can be used. Also, in order to prevent corrosion by the electrolytic solution, it is preferable to coat with nickel or aluminum, etc. Inside the battery can 602, the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. Further, the inside of the battery can 602 where the battery element is provided is filled with a non-aqueous electrolytic solution (not shown). The non-aqueous electrolytic solution can be the same as that used in a coin-type secondary battery. For the positive electrode and negative electrode used in the cylindrical secondary battery, since they are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 6 03 is resistance-welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602 respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature C oefficient) 611.

[0155] Since the positive electrode and negative electrode used in the cylindrical secondary battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 6 03 is resistance-welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602 respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature C oefficient) 611. The safety valve mechanism 612 releases the positive electrode cap 601 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 cuts off the electrical connection between the positive electrode 604 and the positive electrode 604. It is a thermal resistor whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current. It prevents abnormal heat generation. The PTC element is made of barium titanate (BaTiO3) Semiconductor ceramics and the like can be used.

[0156] 5C, a plurality of secondary batteries 600 are mounted on the conductive plate 613 and the conductive plate 614. A module 615 may be formed by sandwiching the secondary batteries 600 between them. They may be connected in series, or may be connected in parallel and then in series. By configuring a module 615 having a plurality of secondary batteries 600, It is possible to extract a large amount of power.

[0157] 5(D) is a top view of the module 615. The conductive plate 613 is dotted for clarity. As shown in FIG. 5(D), the module 615 is a module that electrically connects a plurality of secondary batteries 600. The conductive plate 613 may be placed on the conductive wire 616. In addition, even if a temperature control device 617 is provided between the plurality of secondary batteries 600, When the secondary battery 600 is overheated, the temperature control device 617 cools it down. If 600 is too cold, it can be heated by the temperature control device 617. This makes the performance of the module 615 less susceptible to the outside temperature.

[0158] By using the positive electrode active material 100 described in the previous embodiment for the positive electrode 604, it is possible to achieve high capacity and small capacity. It is possible to obtain a cylindrical secondary battery 600 with excellent discharging characteristics.

[0159] [Structural Example of Secondary Battery] Another structural example of the secondary battery will be described with reference to FIGS. 6 to 9.

[0160] FIGS. 6(A) and 6(B) are views showing the external appearance of a battery pack. The battery pack has a circuit substrate 900 and a secondary battery 913. The secondary battery 913 has a terminal 951 and a terminal 9 52 and is covered with a label 910. The battery pack may also have an antenna 914.

[0161] The circuit substrate 900 is fixed with a seal 915. The circuit substrate 900 has a circuit 912. The terminal 911 is electrically connected to the terminals 951 and 952 of the secondary battery 913 via the circuit substrate 900. The terminal 911 is also electrically connected to the antenna 914 and the circuit 912 via the circuit substrate 900. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0162] The circuit 912 has, for example, a function as a protection circuit that protects the secondary battery 913 from overcharging, over-discharging, and overcurrent. The circuit 912 may be provided on the back surface of the circuit substrate 900. Note that the antenna 914 is not limited to a coil shape, and may be, for example, linear or plate-shaped. Also, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. The antenna 914 has a function capable of performing data communication with, for example, an external device. The battery pack and via the antenna 914 ​​​As a communication method with other devices, a response method that can be used between the battery pack and other devices, such as NFC, can be applied.

[0163] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of being able to shield the electromagnetic field generated by the secondary battery 913, for example. The layer 916 can be made of, for example, a magnetic material.

[0164] Note that the structure of the battery pack is not limited to that shown in FIG. 6.

[0165] For example, as shown in FIGS. 7(A-1) and 7(A-2), an antenna 918 may be provided on a pair of opposing surfaces of the secondary battery 913 shown in FIGS. 6(A) and 6(B). FIG. 7(A-1) is an external view seen from one side direction of the pair of surfaces, and FIG. 7(A-2) is an external view seen from the other side direction of the pair of surfaces. For the same parts as those shown in FIGS. 6(A) and 6(B), the description of the battery pack shown in FIGS. 6(A) and 6(B) can be appropriately incorporated.

[0166] As shown in FIG. 7(A-1), the antenna 914 is provided with the layer 916 sandwiched between a pair of surfaces of the secondary battery 913, and as shown in FIG. 7(A-2), the other side of the pair of surfaces of the secondary battery 913 is provided with the antenna 918 with the layer 917 sandwiched therebetween. The layer 917 has a function of being able to shield the electromagnetic field generated by the secondary battery 913, for example. The layer 917 can be made of, for example, a magnetic material.

[0167] With the above structure, two antennas can be provided in the battery pack, and the sizes of both the antenna 914 and the antenna 918 can be increased.​​​​​​

[0168] Antenna 918 can apply an antenna with a shape applicable to antenna 914. . Furthermore, antenna 918 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. That is, antenna 914 may be made to function as one of the two conductors of the capacitor. Thereby, power can be exchanged not only by the electromagnetic field and magnetic field but also by the electric field.

[0169] Alternatively, as shown in Fig. 7(B-1), a display device 920 may be provided in the battery pack shown in Figs. 6(A) and 6(B). The display device 920 is electrically connected to terminal 911. Note that, for the same parts as those of the battery pack shown in Figs. 6(A) and 6(B), the description of the battery pack shown in Figs. 6(A) and 6(B) can be appropriately cited.

[0170] The display device 920 may display, for example, an image indicating whether it is being charged or not, an image indicating the power storage amount, etc. As the display device 920, for example, an electronic paper, a liquid crystal display device, an electroluminescence (also referred to as EL) display device, etc. can be used. For example, by using an electronic paper, the power consumption of the display device 920 can be reduced.

[0171] Alternatively, as shown in Fig. 7(B-2), a sensor 921 may be provided in the secondary battery 913 shown in Figs. 6(A) and 6(B). The sensor 921 is electrically connected to terminal 911 via terminal 922 and circuit board 900. Note that, for the same parts as those of the power storage device shown in Figs. 6(A) and 6(B), the description of the power storage device shown in Figs. 6(A) and 6(B) can be appropriately cited. . ​​​​​​​​​​​​

[0172] As the sensor 921, for example, it may have a function capable of measuring displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light , liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. By providing the sensor 921, for example, data (such as temperature) indicating the environment where the power storage device is placed can be detected and stored in the memory in the circuit 912.

[0173] Furthermore, a structural example of the secondary battery 913 will be described with reference to FIGS. 8 and 9.

[0174] The secondary battery 913 shown in FIG. 8(A) has a wound body 950 provided with a terminal 951 and a terminal 952 inside a housing 930. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In FIG. 8(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminal 951 and the terminal 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

[0175] Note that, as shown in FIG. 8(B), the housing 930 shown in FIG. 8(A) may be formed of a plurality of materials. For example, the secondary battery 913 shown in FIG. 8(B) has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the region surrounded by the housing 930a and the housing 930b.

[0176] The housing 930a can be made of an insulating material such as organic resin. By using a material such as organic resin on the surface on which the secondary battery 913 is formed, If the shielding of the electric field by the housing 930a is small, the shielding of the electric field by the housing 930a can be suppressed. Antennas such as antenna 914 and antenna 918 may be provided inside the housing 930b. For example, a metal material can be used.

[0177] Furthermore, the structure of the wound body 950 is shown in FIG. 9. The wound body 950 includes a negative electrode 931 and a positive electrode The winding body 950 has a separator 932 and a separator 933. A negative electrode 931 and a positive electrode 932 are stacked one on top of the other, and the laminated sheet is wound to form a wound body. The negative electrode 931, the positive electrode 932, and the separator 933 may be stacked in a plurality of layers. May be layered.

[0178] The negative electrode 931 is connected to the terminal 911 shown in FIG. 6 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG. Connected.

[0179] By using the positive electrode active material described in the above embodiment for the positive electrode 932, it is possible to achieve high capacity cycling. The secondary battery 913 can have excellent characteristics.

[0180] [Laminated secondary battery] Next, an example of a laminated secondary battery will be described with reference to FIGS. If the laminated secondary battery is made flexible, it will have at least one flexible portion. If the secondary battery is mounted in an electronic device that also has a battery, the secondary battery can be bent according to the deformation of the electronic device. can.

[0181] With reference to FIG. 10, the laminated secondary battery 980 will be described. The laminated secondary battery 980 has a wound body 993 shown in FIG. 10(A). The wound body 993 includes a negative electrode 994 , a positive electrode 995, and a separator 996. The wound body 993 is similar to the wound body 950 described in FIG. 9, in which the negative electrode 994 and the positive electrode 995 overlap with each other with the separator 996 interposed therebetween, and the laminated sheet is wound.

[0182] Note that the number of laminations of the laminate composed of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required capacity and the element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of a lead electrode 997 and a lead electrode 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrode 997 and the lead electrode 998.

[0183] As shown in FIG. 10(B), the wound body 993 described above is housed in a space formed by thermocompression bonding or the like a film 981 serving as an exterior body and a film 98 2 having a recess, whereby the secondary battery 980 shown in FIG. 10(C) can be manufactured. The wound body 99 3 has a lead electrode 997 and a lead electrode 998, and is impregnated with an electrolytic solution inside the film 981 and the film 982 having a recess.

[0184] For the film 981 and the film 982 having a recess, a metal material such as aluminum or a resin material can be used. If a resin material is used as the material of the film 981 and the film 982 having a recess, when a force is applied from the outside, the film 981 and the recess The film 982 can be deformed, and a flexible secondary battery can be manufactured. This is achievable.

[0185] Also, although FIGS. 10(B) and 10(C) show examples using two films, a space can be formed by bending a single film, and the above-described winding body 99 3 can be housed in the space.

[0186] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, a secondary battery 980 with high capacity and excellent cycle characteristics can be obtained.

[0187] Also, in FIG. 10, an example of a secondary battery 9 80 having a winding body in a space formed by a film serving as an exterior body was described. However, for example, as shown in FIG. 11, a secondary battery having a plurality of strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film serving as an exterior body may also be used. This is acceptable.

[0188] The laminated secondary battery 500 shown in FIG. 11(A) includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte 508, and an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509 . Also, the interior of the exterior body 509 is filled with the electrolyte 508. As the electrolyte 508, the electrolyte shown in Embodiment 2 can be used. In the laminated secondary battery 500 shown in FIG. 11(A), the positive electrode current collector 501 and the negative

[0189] electrode current collector 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, the positive electrode A part of the current collector 501 and the negative electrode current collector 504 may be exposed to the outside from the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed to the outside from the exterior body 509, and the lead electrode may be ultrasonically bonded to the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 so that the lead electrode is exposed to the outside. In the laminated secondary battery 500, the exterior body 509 is provided with a metal thin film excellent in flexibility, such as aluminum, stainless steel, copper, or nickel, on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide. Further, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the exterior body on the metal thin film. A three-layer laminated film can be used.

[0190]

[0191]

[0192]

[0192] Combined, it can be made into a secondary battery that can be thinned and has excellent flexibility.

[0193] Here, an example of the external view of the laminated secondary battery 500 is shown in FIGS. 12 and 13. FIG. 1 12 and FIG. 13 have a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0194] FIG. 14(A) shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 50 1, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. Also, the positive electrode 503 has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504 and is formed. Also, the negative electrode 506 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region region. The area and shape of the tab regions of the positive electrode and the negative electrode are not limited to the examples shown in FIG. 14(A).

[0195] [Manufacturing method of laminated secondary battery] Here, an example of the manufacturing method of the laminated secondary battery whose external view is shown in FIG. 12 will be described with reference to FIGS. 14 (B) and (C).

[0196] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 14(B) shows the laminated negative electrode 506, separator 507, and positive electrode 503. Here, an example of using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. Next, the joining of the tab regions of the positive electrode 503 to each other and the joining of the positive electrode lead electrode 510 to the tab region of the outermost positive electrode are performed. For the joining, for example, ultrasonic welding or the like can be used. Similarly, the joining of the tab regions of the negative electrode 506 to each other and the joining of the negative electrode lead to the tab region of the outermost negative electrode are performed. ​Perform the bonding of the anode electrode 511.

[0197] Next, arrange the negative electrode 506, the separator 507, and the positive electrode 503 on the exterior body 509.

[0198] Next, as shown in Fig. 14(C), bend the exterior body 509 at the portion indicated by the dashed line. After that, bond the outer peripheral portion of the exterior body 509. For bonding, for example, thermocompression bonding or the like may be used. At this time , provide a region (hereinafter referred to as the inlet) that is not bonded to a part (or one side) of the exterior body 509 so that the electrolyte 508 can be filled later.

[0199] Next, introduce the electrolyte 508 into the interior of the exterior body 509 through the inlet provided in the exterior body 509. The introduction of the electrolyte 508 is preferably carried out under a reduced-pressure atmosphere or an inert gas atmosphere. And finally, bond the inlet. In this way, a secondary battery 500, which is a laminated secondary battery, can be manufactured.

[0200] By using the positive electrode active material described in the previous embodiment for the positive electrode 503, a secondary battery 500 with high capacity and excellent cycle characteristics can be obtained.

[0201] [Bendable Secondary Battery] Next, an example of a bendable secondary battery will be described with reference to Figs. 15 and 16. .

[0202] Fig. 15(A) shows a schematic top view of a bendable battery 250. Figs. 15(B1), (B2), and (C) are schematic cross-sectional views taken along the cut lines C1-C2, cut lines C3-C4 and cut lines A1-A2 in Fig. 15(A), respectively. The battery 250 includes an exterior body 251 and an exterior body It has a positive electrode 211a and a negative electrode 211b housed inside 251. The positive electrode 211a and the electrically connected lead 212a, and the negative electrode 211b and the electrically connected lead 21 2b extend outside the exterior body 251. Also, in the region surrounded by the exterior body 251, in addition to the positive electrode 211a and the negative electrode 211b, an electrolytic solution (not shown) is enclosed.

[0203] The positive electrode 211a and the negative electrode 211b of the battery 250 will be described with reference to FIG. 16. FIG. 16(A) is a perspective view for explaining the lamination order of the positive electrode 211a, the negative electrode 211b, and the separator 214. FIG. 16(B) is a perspective view showing the leads 2 12a and 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0204] As shown in FIG. 16(A), the battery 250 has a plurality of strip-shaped positive electrodes 211a, a plurality of strip-shaped negative electrodes 211b, and a plurality of separators 214. The positive electrode 211a and the negative electrode 211 b each have a protruding tab portion and a portion other than the tab. On the surface of one side of the positive electrode 211a other than the tab, a positive electrode active material layer is formed, and on the surface of one side of the negative electrode 211b other than the tab, a negative electrode active material layer is formed.

[0205] The positive electrode 211a and the negative electrode 211b are laminated so that the surfaces of the positive electrode 211a where the positive electrode active material layer is not formed face each other, and the surfaces of the negative electrode 211b where the negative electrode active material is not formed face each other. are laminated.

[0206] Also, a separator 214 is provided between the surface of the positive electrode 211a where the positive electrode active material is formed and the surface of the negative electrode 211b where the negative electrode active material is formed. In FIG. 16(A), the separator 214 is shown by a dotted line for easy viewing. ​​​

[0207] Also, as shown in FIG. 16(B), the plurality of positive electrodes 211a and the leads 212a are electrically connected at the joint 215 a. Also, the plurality of negative electrodes 211b and the leads 212b are electrically connected at the joint 2 15b.

[0208] Next, the exterior body 251 will be described with reference to FIGS. 15(B1), (B2), (C), and (D).

[0209] The exterior body 251 has a film-like shape and is bent in two so as to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a bent portion 261, a pair of seal portions 2 62, and a seal portion 263. The pair of seal portions 262 are provided with the positive electrode 211a and the negative electrode 211b interposed therebetween and can also be called side seals. Also, the seal portion 26 3 has a portion overlapping the leads 212a and the leads 212b and can also be called a top seal.

[0210] The exterior body 251 preferably has a corrugated shape in which ridge lines 271 and valley lines 2 72 are alternately arranged in a portion overlapping the positive electrode 211a and the negative electrode 211b. Also, the seal portions 26 2 and the seal portion 263 of the exterior body 251 are preferably flat.

[0211] FIG. 15(B1) is a cross-section cut at a portion overlapping the ridge line 271, and FIG. 15(B2) is a cross-section cut at a portion overlapping the valley line 272. FIGS. 15(B1) and (B2) both correspond to cross-sections in the width direction of the battery 250 and the positive electrode 211a and the negative electrode 211b.

[0212] Here, let the distance between the end portion in the width direction of the negative electrode 211b and the seal portion 262 be the distance La ]​​​. When the battery 250 is deformed such as being bent, as will be described later, the positive electrode 211a and the negative electrode 211b are deformed so as to be displaced from each other in the length direction. At this time, if the distance La is too short, the outer body 251 and the positive electrode 211a and the negative electrode 211b rub strongly, and the outer body 251 may be damaged and break. In particular, when the metal film of the outer body 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is made too large, the volume of the battery 250 will increase and increase.

[0213] Also, the thicker the total thickness of the stacked positive electrode 211a and negative electrode 211b, the more preferable it is to increase the distance La between the negative electrode 211 b and the seal portion 262.

[0214] More specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is defined as thickness t, the distance La is 0.8 times or more and 3.0 times or less of the thickness t, preferably 0.9 times or more and 2.5 times or less, more preferably 1.0 times or more and 2.0 times or less It is preferable that it is below. By setting the distance La within this range, a compact and highly reliable battery against bending can be realized.

[0215] Also, when the distance between the pair of seal portions 262 is defined as distance Lb, it is preferable to make the distance Lb sufficiently larger than the width Wb of the negative electrode 211b. Thereby, when the battery 250 is repeatedly deformed such as being bent even if the positive electrode 211a and the negative electrode 211b come into contact with the outer body 251, a part of the positive electrode 211a and the negative electrode 211b can be displaced in the width direction. Therefore, the positive Effectively prevent the positive electrode 211a and the negative electrode 211b from rubbing against the exterior body 251 This can be achieved.

[0216] For example, the difference between the distance Lb between a pair of seal portions 262 and the width Wb of the negative electrode 211b is preferably 1.6 times or more and 6.0 times or less, more preferably 1.8 times or more and 5.0 times or less, still more preferably 2.0 times or more and 4.0 times or less the thickness t of the positive electrode 211a and the negative electrode 211b. That is, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of the following formula (1). Here, a satisfies 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, more preferably 1.0 or more and 2.0 or less. .

[0217] In other words, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of the following formula (1). .

[0218]

Equation

[0219] Here, a satisfies 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, more preferably 1.0 or more and 2.0 or less. .

[0220] Also, FIG. 15(C) is a cross section including the lead 212a and corresponds to a cross section in the longitudinal direction of the battery 250, the positive electrode 211a, and the negative electrode 211b. As shown in FIG. 15(C), it is preferable that a space 273 is provided between the longitudinal ends of the positive electrode 211a and the negative electrode 211b and the exterior body 251 at the bent portion 261. FIG. 15(D) shows a schematic cross-sectional view when the battery 250 is bent. FIG. 15(D) corresponds to the cross section taken along the cutting line B1-B2 in FIG. 15(A). When the battery 250 is bent, a part of the exterior body 251 located on the outer side of the bend extends, and a part located on the inner side contracts.

[0221] FIG. 15(D) shows a schematic cross-sectional view when the battery 250 is bent. FIG. 15(D) corresponds to the cross section taken along the cutting line B1-B2 in FIG. 15(A). .

[0222] When the battery 250 is bent, a part of the exterior body 251 located on the outer side of the bend extends, and a part located on the inner side Some of the others are deformed so as to shrink. More specifically, the portion located outside the exterior body 251 is deformed such that the amplitude of the wave is small and the period of the wave is large. On the other hand, the exterior body 251 the portion located inside is deformed such that the amplitude of the wave is large and the period of the wave is small . Thus, when the exterior body 251 is deformed, the stress applied to the exterior body 251 due to bending is relaxed, so that the material itself constituting the exterior body 251 does not need to expand and contract. As a result, the exterior body 251 can be bent with a small force without being damaged.

[0223] Also, as shown in FIG. 15(D), when the battery 250 is bent, the positive electrode 211a and the negative electrode 21 1b are relatively displaced from each other. At this time, the plurality of stacked positive electrodes 211a and negative electrodes 211b are displaced such that the amount of displacement increases as they approach the bent portion 261 because one end on the seal portion 263 side is fixed by the fixing member 217. As a result, the stress applied to the positive electrode 21 1a and the negative electrode 211b is relaxed, and the positive electrode 211a and the negative electrode 211b themselves do not need to expand and contract. As a result, the battery 250 can be bent without the positive electrode 211a and the negative electrode 211b being damaged.

[0224] Also, since there is a space 273 between the ends of the positive electrode 211a and the negative electrode 211b and the exterior body 251, when bent, the ends of the positive electrode 211a and the negative electrode 211b located inside can be relatively displaced without contacting the exterior body 251.

[0225] The battery 250 illustrated in FIGS. 15 and 16 is less likely to be damaged, such as damage to the exterior body, damage to the positive electrode 211a and the negative electrode 211b, etc., even when repeatedly bent and stretched, and the battery characteristics are also less likely to deteriorate. It is a battery. By using the positive electrode active material described in the previous embodiment for the positive electrode 211a of the battery 250, a battery with a higher capacity and excellent cycle characteristics can be obtained.

[0226] (Embodiment 4) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device will be described.

[0227] First, an example of mounting a bendable secondary battery, which was partially described in Embodiment 3, on an electronic device is shown in FIG. 17. As an electronic device to which a bendable secondary battery is applied, for example, a television set (also referred to as a TV or television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone ( also referred to as a cellular phone or mobile phone device), a portable game machine, a portable information terminal, an audio playback device, a pachinko machine, and other large game machines such as these can be mentioned.

[0228] In addition, it is also possible to incorporate a secondary battery having a flexible shape along the inner wall or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0229] FIG. 17(A) shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 incorporated in a housing 7401, as well as operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 has a secondary battery 7407. By using the secondary battery of one aspect of the present invention for the secondary battery 7407 described above, a lightweight and long - life mobile phone can be provided.

[0230] ​​​​​Figure 17(B) shows the state in which the mobile phone 7400 is bent. When the mobile phone 740 0 is deformed by an external force and bent as a whole, the secondary battery provided inside it 7407 is also bent. Also, at that time, the state of the bent secondary battery 7407 is shown in Fig. 17(C ). The secondary battery 7407 is a thin rechargeable battery. The secondary battery 7407 is in a bent state and fixed. Incidentally, the secondary battery 7407 has a lead electrode 7408 electrically connected to the current collector 7409 .

[0231] Figure 17(D) shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104 . Also, Fig. 17(E) shows the state of the bent secondary battery 7104. When the secondary battery 7104 is bent and worn on the user's arm, the housing deforms and the curvature of part or all of the secondary battery 7104 changes. Incidentally, the degree of bending at any point on the curve represented by the value of the radius of the corresponding circle is the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, when the radius of curvature is in the range of 40 mm or more and 150 mm or less, part or all of the main surface of the housing or the secondary battery 7104 changes . If the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm or more and 150 mm or less, high reliability can be maintained. By using the secondary battery of one aspect of the present invention for the above secondary battery 7104, a lightweight and long-life portable display device can be provided . .

[0232] Figure 17(F) shows an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 72 05, input / output terminals 7206, etc​

[0233] The mobile information terminal 7200 can execute various applications such as mobile phones, e-mails, text viewing and creation, music playback, Internet communication, and computer games.

[0234] The display unit 7202 is provided with a curved display surface and can perform display along the curved display surface. In addition, the display unit 7202 is equipped with a touch sensor and can be operated by touching the screen with a finger or a stylus. For example, by touching the icon 7207 displayed on the display unit 7202, an application can be launched.

[0235] In addition to time setting, the operation button 7205 can perform various functions such as turning on and off the power, turning on and off wireless communication, executing and canceling the silent mode, and executing and canceling the power-saving mode. For example, the functions of the operation button 7205 can also be freely set by the operating system incorporated in the mobile information terminal 7200.

[0236] In addition, the mobile information terminal 7200 can execute communication-standardized short-range wireless communication. For example, it can communicate with a wireless headset to make hands-free calls.

[0237] In addition, the mobile information terminal 7200 is equipped with an input / output terminal 7206 and can directly exchange data with other information terminals via a connector. In addition, charging can also be performed via the input / output terminal 7206. Note that the charging operation may also be performed by wireless power supply without passing through the input / output terminal 7206.

[0238] The display unit 7202 of the mobile information terminal 7200 has a secondary battery according to one aspect of the present invention. By using the secondary battery according to one aspect of the present invention, a lightweight and long-life mobile information terminal can be provided. For example, the secondary battery 7104 shown in FIG. 17(E) can be incorporated in a curved state inside the housing 7201 or in a state where it can be curved inside the band 7203.

[0239] The mobile information terminal 7200 preferably has a sensor. Examples of the sensor include human body sensors such as fingerprint sensors, pulse sensors, body temperature sensors, etc., and touch sensors, pressure sensors, acceleration sensors, etc. are preferably mounted.

[0240] FIG. 17(G) shows an example of a bracelet-type display device. The display device 7300 has a display unit 7 304 and has a secondary battery according to one aspect of the present invention. Further, the display device 7300 can be provided with a touch sensor on the display unit 7304, and can also function as a mobile information terminal.

[0241] The display surface of the display unit 7304 is curved, and display can be performed along the curved display surface. Further, the display device 7300 can change the display state by means of communication-standardized short-range wireless communication or the like.

[0242] The display device 7300 is provided with input / output terminals and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminals. Note that the charging operation may be performed by wireless power supply without passing through the input / output terminals.

[0243] By using the secondary battery according to one aspect of the present invention as the secondary battery of the display device 7300, it is lightweight. ​​A display device with a long lifespan can be provided in terms of quantity.

[0244] Next, FIGS. 18(A) and 18(B) show an example of a foldable tablet terminal. The tablet terminal 9600 shown in FIGS. 18(A) and 18(B) includes a housing 9630a, a housing 9630b, a movable part 9640 connecting the housing 9630a and the housing 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 wider display unit can be achieved. FIG. 18(A) shows the tablet terminal 9600 in an open state, and FIG. 18(B) shows the tablet terminal 9600 in a closed state.

[0245] Also, the tablet terminal 9600 has a power storage body 9635 inside the housing 9630a and the housing 9630b. The power storage body 9635 is provided through the movable part 9640 and extends across the housing 9630a and the housing 9630b.

[0246] A part of the display unit 9631 can be a touch panel area, and data can be input by touching the displayed operation keys. Also, by touching the position where the keyboard display switching button of the touch panel is displayed with a finger or a stylus, etc., the keyboard buttons can be displayed on the display unit 9631.

[0247] Also, the display mode switching switch 9626 can select switching of the display orientation such as vertical display or horizontal display, and switching between black-and-white display and color display. The power saving mode switching switch The touch 9625 can optimize the display brightness according to the amount of external light detected by the optical sensor built into the tablet terminal 9600 during use. The tablet terminal can incorporate not only an optical sensor but also other detection devices such as sensors for detecting inclination, such as a gyro and an acceleration sensor.

[0248] Figure 18(B) shows a closed state, and the tablet terminal includes a housing 9630, a solar cell 96 33, and a charge / discharge control circuit 9634 including a DCDC converter 9636. Also, as the power storage body 9635, a secondary battery according to an aspect of the present invention is used.

[0249] Since the tablet terminal 9600 is foldable in two, it can be folded so that the housing 9630a and the housing 9630b overlap each other when not in use. By folding, the display unit 9631 can be protected, thus enhancing the durability of the tablet terminal 9600. Also, since the power storage body 9635 using the secondary battery according to an aspect of the present invention has a high capacity and good cycle characteristics, a tablet terminal that can be used for a long time over a long period can be provided.

[0250] In addition, the tablet terminals shown in FIGS. 18(A) and 18(B) can also have various functions, such as a function of displaying various information (still images, moving images, text images, etc.), a function of displaying a calendar, date, or time on the display unit, a touch input function of touch input operating or editing the information displayed on the display unit, a function of controlling processing by various software (programs), and the like.

[0251] The solar cell 9633 attached to the surface of the tablet terminal generates power for the touch panel, ​​​​It can be supplied to a display unit, a video signal processing unit, etc. Note that the solar cell 9633 can be provided on one side or both sides of the housing 9630, and can be configured to efficiently charge the power storage body 9635.

[0252] Also, the configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 18(B) will be described with reference to the block diagram in Fig. 18( C). Fig. 18(C) shows the solar cell 9633, the power storage body 963 5, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631. The power storage body 9635, the DCDC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the parts of the charge / discharge control circuit 96 34 shown in Fig. 18(B).

[0253] First, an example of the operation when power is generated by the solar cell 9633 due to external light will be described. The power generated by the solar cell is stepped up or down by the DCDC converter 9636 to obtain a voltage for charging the power storage body 9635. When the power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 9637 steps up or down the voltage to the required voltage for the display unit 9631. When the display on the display unit 9631 is not performed, SW1 can be turned off and SW2 can be turned on to charge the power storage body 9635.

[0254] Note that the solar cell 9633 is shown as an example of a power generation means, but it is not particularly limited, and the power storage body 9635 can be charged by other power generation means such as a piezoelectric element (piezoelectric element) or a thermoelectric conversion element (Peltier element). For example, a configuration for wireless (non-contact) power transmission and reception can also be used. ​​​​It may be configured to include a contactless power transmission module for charging or to combine other charging means. It may also be.

[0255] FIG. 19 shows an example of another electronic device. In FIG. 19, the display device 8000 is an example of an electronic device using the secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 800 0 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, etc. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can be supplied with power from a commercial power source, or can use the power stored in the secondary battery 8004. Therefore , even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power supply, the display device 8000 can be used . The display unit 8002 may be a light-emitting device having a light-emitting element such as a liquid crystal display device, an organic EL element, etc. in each pixel, an electrophoretic display device, a DMD (Digital Micromirror Devi ce), a PDP (Plasma Display Panel), a FED (Field

[0256] Emission Display), etc., and a semiconductor display device can be used. In addition to being used for receiving TV broadcasts, the display device includes all display devices for information display, such as those for personal computers and advertising displays. ce), PDP (Plasma Display Panel), FED (Field Emission Display), etc.

[0257] Note that the display device includes all display devices for information display, such as those for personal computers and advertising displays, in addition to those for receiving TV broadcasts.

[0258] In FIG. 19, the stationary lighting device 8100 is a secondary battery 81 according to one aspect of the present invention. This is an example of an electronic device using 03. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, etc. In FIG. 19, the case where the secondary battery 8103 is provided inside the ceiling 8104 where the housing 81 01 and the light source 8102 are installed is illustrated , but the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power supply from a commercial power source, or can use the power stored in the secondary battery 8103. Therefore, even when the power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power supply , the lighting device 8100 can be used. Note that in FIG. 19, the installed lighting device 8100 provided on the ceiling 8104 is illustrated

[0259] , but the secondary battery according to one aspect of the present invention can also be used for installed lighting devices provided on the side wall 8105, the floor 8 106, the window 8107, etc., other than the ceiling 8104, and can also be used for desktop type lighting devices and the like. In addition, as the light source 8102, an artificial light source that artificially obtains light using power can be used

[0260] . Specifically, incandescent bulbs, discharge lamps such as fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements can be cited as examples of the above artificial light sources. In FIG. 19, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is

[0261] an example of an electronic device using a secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, etc. In FIG. 19 , illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, but the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power supply from a commercial power source, or can use the power stored in the secondary battery 8203. In particular, when the secondary battery 82 03 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8203 according to an aspect of the present invention as an uninterruptible power supply, the air conditioner can be used.

[0262] Note that in FIG. 19, a separate type air conditioner composed of an indoor unit and an outdoor unit is illustrated, but the secondary battery according to an aspect of the present invention can also be used in an integrated type air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0263] In FIG. 19, the electric refrigerator 8300 is an example of an electronic device using the secondary battery 8304 according to an aspect of the present invention. Specifically, the electric refrigerator 8300 includes a housing 8301, a door for the storage room 8302, a door for the freezer room 8303, the secondary battery 8304, and the like. In FIG. 19, the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator 8300 can receive power supply from a commercial power source, or can use the power stored in the secondary battery 8304. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8304 according to an aspect of the present invention as an uninterruptible power supply, the electric refrigerator 8300 can be used. ​​​​

[0264] In addition, during times when electronic devices are not in use, especially when the total amount of power that can be supplied by the commercial power supplier is low, During the time period when the ratio of the amount of electricity actually used (called the electricity usage rate) is low, By storing power in the battery, it is possible to prevent power usage rates from increasing outside of the above time periods. For example, in the case of the electric refrigerator-freezer 8300, when the temperature is low and the refrigerator compartment door 830 2. During the night when the freezer door 8303 is not opened or closed, the secondary battery 8304 stores power. Then, as the temperature rises, the refrigerator door 8302 and the freezer door 8303 are opened and closed. By using the secondary battery 8304 as an auxiliary power source during the daytime, the daytime power usage rate can be kept low.

[0265] In addition to the electronic devices described above, the secondary battery according to one embodiment of the present invention can be mounted in various electronic devices. According to one embodiment of the present invention, the cycle characteristics of the secondary battery can be improved. According to this aspect, a high-capacity secondary battery can be obtained, and therefore the secondary battery itself can be made small and lightweight. Therefore, the secondary battery according to one embodiment of the present invention can be By incorporating this technology into electronic devices, the electronic devices can be made lighter and have a longer lifespan. The embodiment can be implemented in appropriate combination with other embodiments.

[0266] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle will be described.

[0267] When a secondary battery is installed in a vehicle, it becomes a hybrid vehicle (HEV), an electric vehicle (EV), or a powertrain. This will enable the realization of next-generation clean energy vehicles such as plug-in hybrid vehicles (PHEVs). 。

[0268] In FIG. 20, a vehicle using a secondary battery, which is one aspect of the present invention, is illustrated. FIG. 20(A) The automobile 8400 shown is an electric vehicle that uses an electric motor as a power source for running Or it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for running By using one aspect of the present invention, a vehicle with a long cruising range can be realized In addition, the automobile 8400 has a secondary battery. The secondary battery May be arranged and used with respect to the floor portion inside the vehicle, the modules of the secondary battery shown in FIGS. 12(C) and 12(D) Alternatively, a battery pack in which a plurality of secondary batteries shown in FIG. 17 are combined may be installed with respect to the floor portion inside the vehicle The secondary battery not only drives the electric motor 8406 But also can supply power to light-emitting devices such as the headlight 8401 and the room light (not shown)

[0269] In addition, the secondary battery can supply power to display devices such as the speedometer and tachometer of the automobile 8400 In addition, the secondary battery can supply power to semiconductor devices such as the navigation system of the automobile 8400

[0270] The automobile 8500 shown in FIG. 20(B) can be charged by receiving power supply from an external charging facility by a plug-in method, a non-contact power supply method, etc. to the secondary battery of the automobile 8500 FIG. 20(B) shows a state in which charging is being performed from a ground-mounted charging device 8021 to a secondary battery 8024 mounted on the automobile 8500 via a cable 802[[]] When charging The charging method, the specifications of the connector, etc. are predetermined ones such as CHAdeMO (registered trademark) and Combo ​​​ It may be appropriately performed in this manner. The charging device 8021 may be a charging station provided in a commercial facility or may also be a household power source. For example, by plug-in technology, the secondary battery 8024 mounted on the vehicle 8500 can be charged by external power supply. Charging can be performed by converting AC power into DC power through a conversion device such as an AC-DC converter and the like.

[0271] Also, although not shown, a power receiving device may be mounted on the vehicle, and power may be supplied non-contact from a power transmission device on the ground for charging. In the case of this non-contact power supply method, by incorporating the power transmission device into a road or an outer wall charging can be performed not only while the vehicle is stopped but also while it is running. Also, using this non-contact power supply method, power may be transmitted and received between vehicles. Further, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or running. For such non-contact power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0272] Also, FIG. 20(C) is an example of a two-wheeled vehicle using a secondary battery according to an aspect of the present invention. The scooter 8600 shown in FIG. 20 (C) includes a secondary battery 8602, a side mirror 8601, and a direction indicator lamp 8603. The secondary battery 8602 can supply electricity to the direction indicator lamp 8603 and the like.

[0273] Also, the scooter 8600 shown in FIG. 20(C) can store the secondary battery 860 2 in the under-seat storage 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small . The secondary battery 8602 is removable Preferably, during charging, the secondary battery 8602 is carried indoors for charging and stored before driving. Preferably, it is stored before driving.

[0274] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be reduced in size and weight. If the secondary battery itself can be reduced in size and weight, it contributes to reducing the weight of the vehicle, thereby improving the cruising range. In addition, the secondary battery mounted on the vehicle can also be used as a power supply other than the vehicle. In this case, for example, it is possible to avoid using the commercial power supply during the peak of power demand. If it is possible to avoid using the commercial power supply during the peak of power demand, it can contribute to energy saving and reduction of carbon dioxide emissions. In addition, if the cycle characteristics are good, the secondary battery can be used for a long time, so the amount of use of rare metals such as cobalt can be reduced. Preferably, it is stored before driving. If the secondary battery itself can be reduced in size and weight, it contributes to reducing the weight of the vehicle, thereby improving the cruising range. In addition, the secondary battery mounted on the vehicle can also be used as a power supply other than the vehicle. In this case, for example, it is possible to avoid using the commercial power supply during the peak of power demand. If it is possible to avoid using the commercial power supply during the peak of power demand, it can contribute to energy saving and reduction of carbon dioxide emissions. In addition, if the cycle characteristics are good, the secondary battery can be used for a long time, so the amount of use of rare metals such as cobalt can be reduced. Preferably, it is stored before driving. Preferably, it is stored before driving.

[0275] This embodiment can be implemented in appropriate combination with other embodiments.

Example

[0276] In this example, cobalt was applied as the transition metal in the first region of the positive electrode active material. Then, a positive electrode active material prepared by adding magnesium and fluorine to the starting material, and a positive electrode active material prepared without adding magnesium and fluorine as a comparative example were prepared and their characteristics were analyzed. In addition, the cycle characteristics were evaluated by changing the concentrations of magnesium and fluorine added to the starting material. In addition, the cycle characteristics were evaluated by changing the concentrations of magnesium and fluorine added to the starting material. Preferably, it is stored before driving.

[0277] <Preparation of positive electrode active materials of Samples 1 to 6> Cathode active materials from Sample 1 to Sample 6 were prepared by changing the concentrations of the magnesium source and the fluorine source. Lithium carbonate and cobalt oxide were used as common starting materials. Magnesium oxide and lithium fluoride were used as different added starting materials for each sample. For Sample 1, magnesium oxide and lithium fluoride were used as added starting materials so that 0.5 atomic% of magnesium and 1 atomic% of fluorine were contained in the cobalt included in the common starting materials. Hereinafter, Sample 1 will be described as using 0.5 mol% MgO and 1 mol% LiF as added starting materials. As described above in this specification etc., the amount of the added starting material will be indicated by atomic% or mol% with respect to the transition metal contained in the common starting materials. The same notation will be used for Samples 2 and later.

[0278]

[0279]

[0280] For Sample 2, 0.5 mol% MgO and 0.5 mol% LiF with respect to cobalt were used as added starting materials. For Sample 3, 0.5 mol% MgO and 2 mol% LiF were used as added starting materials. For Sample 4 as a comparative example, 1 mol% LiF was used as the added starting material and no magnesium was added. For Sample 5 as a comparative example, 0.5 mol% MgO was used as the added starting material and no fluorine was added. For Sample 6 as a comparative example, neither magnesium nor fluorine was added. The common starting materials and added starting materials for each sample are shown in Table 1.

[0281]

Table 1

[0282] Regarding the above six samples, in the same manner as the production method described in Embodiment 1, the starting materials were mixed, first heating was performed, after cooling, sieving was carried out, second heating was performed, cooled, recovered, and a positive electrode active material was obtained. The particles during these processes and the positive electrode active material after these processes were analyzed as follows.

[0283] <stem-edx> For Sample 1 and Sample 5 (comparative example), the cross-section near the surface of the particles before the second heating was analyzed using STEM-EDX. Figures 22 and 23 show the STEM-EDX images of Sample 1 and Sample 5 (comparative example) before the second heating, respectively. Figures 22(A) and 2 3(A) are STEM images, Figures 22(B) and 23(B) are magnesium mappings, and Figures 22(C) and 23(C) are fluorine mappings.

[0284] As shown in Figure 22(B), in Sample 1 containing magnesium and fluorine in the starting material, some magnesium was segregated near the surface of the particles even before the second heating. The segregated region was about 1 nm to 2 nm from the surface of the particles.

[0285] On the other hand, as shown in the EDX mapping of Figure 23(B), in Sample 5 containing magnesium but not containing fluorine in the starting material, segregation of magnesium near the surface was not observed.

[0286] As shown in Figures 22(C) and 23(C), for both Sample 1 and Sample 5, fluorine was hardly observed inside the positive electrode active material. This was considered to be because fluorine, which is a light element, is difficult to detect by EDX.

[0287] <X-ray Photoelectron Spectroscopy (XPS)> Next, for Sample 1 and Sample 5 (comparative example), the amount of magnesium near the surface of the positive electrode active material was analyzed before and after the second heating.

[0288] The conditions for XPS analysis were as follows. Measuring device: QuanteraII manufactured by PHI X-ray source: Monochromatic Al (1486.6 eV) Detection area: 100 μmφ Detection depth: Approximately 4 - 5 nm (extraction angle 45°) Measurement spectrum: Wide, Li1s, Co2p, Ti2p, O1s, C1s, F1s, S 2p, Ca2p, Mg1s, Na1s, Zr3d

[0289] The results of quantifying the concentrations of each element using XPS are shown in Table 2. The quantification accuracy is about ±1 atomi c%, and the detection limit is about 1 atomic% depending on the element. Also, for Ca, since the Mg Auger peak separated in the waveform is removed, the quantification error is larger than usual.

[0290] Also, the results of calculating the abundance ratios of each element with cobalt set to 1 are shown in Table 3.

[0291]

Table 2

[0292]

Table 3

[0293] Among the abundance ratios of the elements shown in Table 3, the one for magnesium presented as a graph is shown in Figure 2 4.

[0294] As shown in Table 2, Table 3, and Figure 24, in Sample 1 which has magnesium and fluorine as additive starting materials, even before the second heating, magnesium was present near the surface of the cathode active material measurable by XPS . After the second heating, the amount of magnesium near the surface of the cathode active material further increased. That is, it is considered that the segregation of magnesium to the surface of the cathode active material progressed due to the second heating

[0295] ​ Thus, the positive electrode active material of Sample 1 has a first region inside and a second region in the surface layer portion. The first region has lithium cobaltate, and the second region has magnesium. It was confirmed that it is a positive electrode active material.

[0296] On the other hand, in Sample 5 which has no fluorine as an additive starting material and has only magnesium, magnesium near the surface of the positive electrode active material was below the detection limit both before and after the second heating. Thus, it was revealed that fluorine contained in the starting material has the unexpected effect of segregating magnesium to the surface layer portion of the positive electrode active material.

[0297] <Cycle characteristics> Next, CR2032 type (diameter 20 mm, height 3.2 mm) coin-type secondary batteries 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, Sample 3, Sample 4, and Sample 6, and their cycle characteristics were evaluated.

[0298] For the positive electrode, a slurry obtained by mixing the positive electrode active material prepared above, acetylene black (AB), and polyvinylidene fluoride (PVDF) at a weight ratio of positive electrode active material:AB:PVDF = 95:2.5:2.5 was applied to a current collector.

[0299] Lithium metal was used for the counter electrode.

[0300] As the electrolyte contained in the electrolytic solution, 1 mol / L lithium hexafluorophosphate (LiPF6) was used. In the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was mixed at 2 wt%. This mixture was used.

[0301] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) were used.

[0302] The measurement temperature for the cycle characteristic test was set at 25°C. Charging was performed at a constant current of 68 .5 mA / g and an upper limit voltage of 4.6 V, and then constant voltage charging was performed until the current density reached 1.4 mA / g. Discharging was performed at a constant current of 68.5 mA / g per active material weight and a lower limit voltage of 2.5 V. Charge-discharge was performed for 30 cycles each.

[0303] Figures 25(A) and 25(B) show graphs of the cycle characteristics of secondary batteries using the positive electrode active materials before and after the second heating of Sample 1 and before and after the first heating of Sample 5. Figure 25(A) is a graph of the energy density during charging at 4.6 V, and Figure 25(B) is a graph of the energy density retention rate during charging at 4.6 V. The energy density is the product of the discharge capacity and the average discharge voltage.

[0304] As shown in Figure 25, in Sample 1 having magnesium and fluorine in the added starting material, the cycle characteristics were significantly improved by performing the second heating. Also, the energy density was good.

[0305] This is presumably because, as was also clarified from the above XPS results, the amount of magnesium present near the surface of the positive electrode active material increased by performing the second heating.

[0306] On the other hand, in Sample 5 having only magnesium in the added starting material, no significant difference in cycle characteristics was observed before and after the second heating.

[0307] Next, Figures 26 and 27 show the positive electrode active materials of Samples 1 to 6 after the second heating. The graph of the cycle characteristics of the secondary battery is shown. Fig. 26 is a graph of the energy density when charging at 4.6V and Fig. 27 is a graph of the energy density retention rate when charging at 4.6V.

[0308] As shown in Fig. 26 and Fig. 27, Sample 4 (comparative example) with only fluorine added to the starting material and Sample 5 (comparative example) with only magnesium added showed inferior cycle characteristics compared to Sample 6 (comparative example) without adding both magnesium and fluorine. On the other hand, Samples 1 to 3 with magnesium and fluorine added to the starting material showed good

[0309] cycle characteristics. The best cycle characteristics were shown by Sample 1 with an atomic ratio of magnesium to fluorine of 1:2. Next, Sample 2 with a content ratio of magnesium to fluorine of 1:4 showed good cycle characteristics. Also, as is clear from Fig. 26 not only the cycle characteristics but also the energy density was good. Thus, it became clear that by adding magnesium and fluorine to the starting material, a positive electrode active material showing good cycle characteristics can be obtained. Also, the atomic ratio of magnesium and fluorine contained in the starting material is preferably Mg:F = 1:x (1.5 ≦ x ≦ 4), and it became clear that Mg:F = about 1:2 is most preferable.

[0310] In this way, it became clear that by adding magnesium and fluorine to the starting material, a positive electrode active material showing good cycle characteristics can be obtained. Also, the atomic ratio of magnesium and fluorine contained in the starting material is preferably Mg:F = 1:x (1.5 ≦ x ≦ 4), and it became clear that Mg:F = about 1:2 is most preferable. Next, while keeping the ratio of magnesium and fluorine constant (Mg:F = 1:2), the positive electrode active materials of Sample 7 and Sample 8 were prepared by changing the addition amount.

[0311] <Preparation of positive electrode active materials of Samples 7 and 8> Next, while keeping the ratio of magnesium and fluorine constant (Mg:F = 1:2), the positive electrode active materials of Sample 7 and Sample 8 were prepared by changing the addition amount.

[0312] ​​​Sample 7 used 1 mol% MgO and 2 mol% LiF as the additive starting materials. Sample 8 used 2 mol% MgO and 4 mol% LiF as the additive starting materials. For Samples 7 and 8, the starting materials were mixed in the same manner as the production method described in Embodiment 1, heated for the first time, cooled, sieved, heated for the second time, cooled, collected, and a positive electrode active material was produced, and a secondary battery was produced.

[0313] The common starting materials and additive starting materials of Samples 1, 7, and 8, in which the atomic ratio of magnesium to fluorine in the raw materials is Mg:F = 1:2, and Sample 6 (comparative example) without added magnesium and fluorine are shown in Table 4.

[0314] [Table 4]

[0315] <Cycle characteristics> Graphs of the cycle characteristics of secondary batteries using the positive electrode active materials of Samples 1, 7, 8, and Sample 6 (comparative example) are shown in FIGS. 28(A) and 28(B). FIG. 28(A) is a graph of the energy density during charging at 4.6 V, and FIG. 28(B) is a graph of the energy density retention rate during charging at 4.6 V. As shown in FIGS. 28(A) and 28(B), all the samples in which the atomic ratio of magnesium to fluorine in the raw materials is Mg:F = 1:2 showed good cycle characteristics. Among them, Sample 7, which used 1 mol% MgO and 2 mol% LiF as the additive starting materials, showed the best cycle characteristics, and the energy density retention rate after 30 cycles was 93%. Also,

[0316] ​​​​​As is also clear from Fig. 28(A), not only the cycle characteristics but also the energy density were good. There was.

Example

[0317] In this example, the results of comparing a positive electrode active material having a second region formed by segregation of magnesium with a positive electrode active material having a magnesium oxide layer formed by external coating are shown. Are shown.

[0318] <Positive electrode active material having a second region formed by segregation> As the positive electrode active material having a second region formed by segregation of magnesium, Sample 7 of Example 1 using 1 mol% MgO and 2 mol% LiF as starting materials was used. Was used.

[0319] <Positive electrode active material having external coating MgO> As the positive electrode active material having a magnesium oxide layer formed by external coating, the positive electrode active materials of Sample 9 (comparative example) and Sample 10 (comparative example) obtained by coating magnesium oxide on lithium cobaltate using a polygonal barrel sputter were used. The production methods of Sample 9 (comparative example) and Sample 10 (comparative example) are described below. (Comparative example) and the positive electrode active material of Sample 10 (comparative example) were used. The production methods of Sample 9 (comparative example) and Sample 10 (comparative example) are described below.

[0320] Lithium cobaltate manufactured by Nippon Chemical Industry Co., Ltd. (product name; C-10N) was used. For the polygonal barrel sputter, magnesium oxide was used as the target, and film formation was performed using 450 W of power and Ar and O2 as sputtering gases. The partial pressures of Ar and O2 were 0.6 Pa and 0.5 Pa, respectively. The treatment time was 36 minutes for Sample 9 and 180 minutes for Sample 10. .5 Pa. .

[0321] After STEM observation was performed after the multi-angle barrel sputtering process, in Sample 9, a magnesium oxide layer with a thickness of about 1 nm to 3 nm was attached to the surface of the positive electrode active material. In addition, in Sample 10, a magnesium oxide layer with a thickness of about 6 nm to 8 nm was attached to the surface of the positive electrode active material.

[0322] Thereafter, 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 temperature was raised at 200°C / h, and dry air with a dew point of -109°C was flowed at 10 L / min.

[0323] The conditions of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example) to be compared in this example are shown in Table 5.

[0324]

Table 5

[0325] <stem> The cross-sections of the positive electrode active materials of Sample 7 and Sample 10 (comparative example) were observed using STEM. The STEM images of Sample 7 having a second region formed by segregation are shown in FIGS. 29(A) and 29(B). The STEM images of Sample 10 (comparative example) having a magnesium oxide layer formed by external coating are shown in FIGS. 30(A) and 30(B). In Sample 7, it was possible to observe that the first region and the second region were different regions from the difference in image brightness and the like. As shown in FIG. 29, in Sample 7 having a second region formed by segregation, a second region of about 1 nm to 2 nm was observed.

[0326] In Sample 7, it was possible to observe that the first region and the second region were different regions from the difference in image brightness and the like. As shown in FIG. 29, in Sample 7 having a second region formed by segregation, a second region of about 1 nm to 2 nm was observed. In Sample 7 having a second region formed by segregation, a second region of about 1 nm to 2 nm was observed. In Sample 7 having a second region formed by segregation, a second region of about 1 nm to 2 nm was observed.

[0327] Also in Sample 10 (comparative example), as shown in FIG. 30, it was possible to observe that a magnesium oxide layer was formed on lithium cobaltate from the difference in image brightness and the like. In Sample 10 (comparative example), a magnesium oxide layer of about 8 nm was observed. Also in Sample 10 (comparative example), as shown in FIG. 30, it was possible to observe that a magnesium oxide layer was formed on lithium cobaltate from the difference in image brightness and the like. In Sample 10 (comparative example), a magnesium oxide layer of about 8 nm was observed. In Sample 10 (comparative example), a magnesium oxide layer of about 8 nm was observed.

[0328] In both Sample 7 and Sample 10 (comparative example), the arrangement of cations and anions between different layers was at least partially aligned, and it was observed that the crystal orientations of the first region and the second region were consistent. In both Sample 7 and Sample 10 (comparative example), the arrangement of cations and anions between different layers was at least partially aligned, and it was observed that the crystal orientations of the first region and the second region were consistent. In both Sample 7 and Sample 10 (comparative example), the arrangement of cations and anions between different layers was at least partially aligned, and it was observed that the crystal orientations of the first region and the second region were consistent.

[0329] <Charge and Discharge Characteristics> Using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), secondary batteries were fabricated in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. FIGS. 31(A), 31(B), and 31(C) show graphs of the charge and discharge characteristics of the secondary batteries using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), respectively. Using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), secondary batteries were fabricated in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. FIGS. 31(A), 31(B), and 31(C) show graphs of the charge and discharge characteristics of the secondary batteries using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), respectively. Using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), secondary batteries were fabricated in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. FIGS. 31(A), 31(B), and 31(C) show graphs of the charge and discharge characteristics of the secondary batteries using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), respectively. Using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), secondary batteries were fabricated in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. FIGS. 31(A), 31(B), and 31(C) show graphs of the charge and discharge characteristics of the secondary batteries using the positive electrode active materials of Sample 7, Sample 9 (comparative example), and Sample 10 (comparative example), respectively.

[0330] As shown in FIG. 31, a sample having a second region formed by segregation of magnesium Sample 7 had a larger capacity and better charge-discharge characteristics than sample 9 having a magnesium oxide layer formed by polygonal barrel sputtering and sample 10.

[0331] <Cycle characteristics> Next, FIGS. 32(A) and 32(B) show the results of evaluating 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 test was conducted in the same manner as in Example 1.

[0332] FIG. 32(A) is a graph of the energy density during charging at 4.6 V, and FIG. 32(B) is a graph of the energy density retention rate during charging at 4.6 V. As shown in FIG. 32(B), sample 7 having the second region formed by segregation had extremely better cycle characteristics than sample 9 and sample 10 having a magnesium oxide layer formed by polygonal barrel sputtering. Also, as shown in FIG. 32(A), the energy density was also better for sample 7.

[0333] Thus, it was revealed that the second region formed by segregation of magnesium contributes more to better charge-discharge characteristics and cycle characteristics than the magnesium oxide layer formed by polygonal barrel sputtering.

[0334] From these results, it was speculated that the region containing magnesium formed as a result of segregation of magnesium originally contained in the starting material to the surface contributes more to the stabilization of the crystal structure of lithium cobaltate than the magnesium oxide layer coated from the outside of the lithium cobaltate particles. ​​​​​​​​

Example

[0335] In this example, the characteristics of the positive electrode active material having the second region formed by the segregation of magnesium were clarified by various analyses.

[0336] <Positive electrode active material analyzed> Sample 7 of Example 1, which used 1 mol% MgO and 2 mol% LiF as the additive starting materials, was used as the analysis sample for this example.

[0337] <STEM, FFT> The STEM-FFT images of the cross-section near the surface of the positive electrode active material of Sample 7 having the second region formed by segregation are shown in FIGS. 33 and 34. FIG. 33(A) is the STEM image near the surface of the positive electrode active material, and the FFT (Fast Fourier Transform) image of the region indicated by FFT1 in FIG. 33(A) is FIG. 33(B). A part of the bright spots in the FFT image of FIG. 33(B) is shown in FIG. 33(C) and is designated as A, B, C, and O.

[0338] Regarding the bright spots in the FFT image of the region indicated by FFT1, the measured values were: for OA, d = 0.20 nm; for OB, d = 0.24 nm; and for OC, d = 0.25 nm. Also, ∠AOB = 53°, ∠BOC = 74°, and ∠AOC = 127°.

[0339] This is from the data of magnesium oxide (MgO) in the ICDD (International Centre for Diffraction Data) database (ICDD45 - 0945), where for OA(200), d = 0.21 nm; for OB(1 - 11), d = 0.24 nm; for OC(-1 - 11), d = 0.24 nm; and ∠AOB = 55°. °, ∠BOC = 70°, and ∠AOC = 125°. Therefore, the area shown by FFT1 is an area having a rock-salt type crystal structure and was found to be an image of

[0011] incidence .

[0340] Fig. 34(A) is the same STEM image near the surface of the positive electrode active material as Fig. 33(A), and the FFT image of the area shown by FFT2 in Fig. 34( A) is Fig. 34(B). Some of the bright spots in the FFT image in Fig. 34(B) are called A, B, C, and O as shown in Fig. 34(C).

[0341] Regarding the bright spots in the FFT image of the area shown by FFT2, the measured values were respectively, OA with d = 0.2 4 nm, OB with d = 0.20 nm, and OC with d = 0.45 nm. Also, ∠AOB = 2 5°, ∠BOC = 53°, and ∠AOC = 78°.

[0342] This is close to the data of lithium cobaltate (LiCoO2) in the ICDD database ( ICDD50 - 0653), where d for OA(101) is 0.24 nm, OB( 104) is 0.20 nm, OC(003) is 0.47 nm, ∠AOB = 25°, ∠BOC = 55°, and ∠AOC = 80°. Therefore, the area shown by FFT2 is an area having lithium cobaltate and was found to be an image of

[0010] incidence.

[0343] Also, from the STEM images in Fig. 33(A) and Fig. 34(A), it was observed that the brightness of the images differed between the first area and the second area, and furthermore, it was observed that the crystal orientations were consistent in the first area and the second area.

[0344] <stem-edx> Next, the results of analyzing the vicinity of the surface and the vicinity of crystal defects of Sample 7 using STEM-EDX are shown in FIGS. 35 to 37. The results are shown in FIGS. 35 to 37.

[0345] FIG. 35 shows the STEM-EDX analysis results of the vicinity of the surface of the positive electrode active material of Sample 7. FIG. 35 (A) is a STEM image, FIG. 35(B) is a mapping of magnesium, and FIG. 35(C) is a mapping of fluorine. is a mapping of fluorine.

[0346] For Sample 1 (FIG. 22) using the starting material added with 0.5 mol% MgO and 1 mol% LiF in Example 1, compared with Sample 7 (FIG. 35) using the starting material added with 1 mol% MgO and 2 mol% LiF, magnesium in the vicinity of the surface of the positive electrode active material was more clearly observed in Sample 7 (FIG. 35). This supports the result of Example 1 that the cycle characteristics are better as the amount of magnesium in the vicinity of the surface of the positive electrode active material increases. magnesium in the vicinity of the surface of the positive electrode active material was more clearly observed. This supports the result of Example 1 that the cycle characteristics are better as the amount of magnesium in the vicinity of the surface of the positive electrode active material increases. This supports the result of Example 1 that the cycle characteristics are better as the amount of magnesium in the vicinity of the surface of the positive electrode active material increases. This supports the result of Example 1 that the cycle characteristics are better as the amount of magnesium in the vicinity of the surface of the positive electrode active material increases.

[0347] FIG. 36 is a cross-sectional TEM image of the vicinity of the crystal defect of the positive electrode active material of Sample 7. In the crystal defect 1001 in the figure, a portion with a different brightness from the others considered to be crystal defects was observed. In the crystal defect 1001 in the figure, a portion with a different brightness from the others considered to be crystal defects was observed.

[0348] The results of analyzing the portion of the crystal defect 1001 in FIG. 36 using STEM-EDX are shown in FIG. 37. shown in FIG. 37.

[0349] FIG. 37(A-1) is a STEM image of the crystal defect 1001 portion, FIG. 37(A-2) is a mapping of magnesium, FIG. 37(B-1) is a mapping of fluorine, and FIG. 37(B-2) is a mapping of zirconium. is a mapping of magnesium, FIG. 37(B-1) is a mapping of fluorine, and FIG. 37(B-2) is a mapping of zirconium. is a mapping of zirconium.

[0350] As shown in FIG. 37(A-2), in the crystal defect and its vicinity of the positive electrode active material of Sample 7, , segregation of magnesium was observed. Therefore, it was shown that Sample 7 is a positive electrode active material having a second region not only near the surface but also inside the sample. Also, as shown in Fig. 37(B-2), a large amount of segregation of zirconium was also observed in the second region inside the sample. The process of mixing the starting materials is carried out by a ball mill, and since zirconium is used as the material of the ball mill, there is a possibility that zirconium has been mixed into Sample 7. Also, as shown in Fig. 37(B-1 ), almost no fluorine was detected in the second region inside the sample. This was considered to be because fluorine, which is a light element, is difficult to detect by EDX. )

[0351] <tof-sims> Next, for the positive electrode active material of Sample 7 having the second region formed by segregation, mag To examine the depth direction distribution of nesium and fluorine, analysis was performed using ToF-SIMS The results are shown in Fig. 38.

[0352] Using a plurality of positive electrode active material particles as samples, ToF-SIMS analysis and sputtering were alternately repeatedly, and analysis was performed in the depth direction from the surface of the positive electrode active material. The measuring device was TOF.S IMS5-300 (manufactured by ION-TOF), and Cs was used as the ion source for sputtering Analysis was also performed in a range of about 50 μm square.

[0353] Magnesium oxide ion ([MgO2] 2- ) and fluorine ion (F - ) intensities are plotted in Fig. 38 with the horizontal axis being the number of measurements (number of cycles). In this measurement, since analysis is being performed on negative ions, the distribution of magnesium is evaluated by the intensity of [MgO2] 2- . Each intensity is normalized with the maximum value set to 1. As shown in Fig. 38, in Sample

[0354] 7 having the second region formed by magnesium segregation, it is clearly shown that the depth direction distributions and peaks of magnesium and fluorine overlap .

[0355] <xps> Next, regarding the positive electrode active material of Sample 7, the results of analysis using XPS before and after the second heating are shown in Table 6 and FIG. 39. The XPS analysis was performed in the same manner as in Example 1.

[0356] The results of quantifying the concentration of each element in Sample 7 using XPS are shown in Table 6. The quantification accuracy is about ±1 atomic%, and the detection limit is about 1 atomic% depending on the element. Also, for Ca, the Mg Auger peak separated by waveform is removed, so the quantification error is larger than usual.

[0357]

Table 6

[0358] The quantitative values in Table 6 exist in the range from a depth of 4 nm to 5 nm from the surface of the positive electrode active material towards the center, which can be analyzed by XPS, and are the numerical values when the total amount of lithium, cobalt, titanium, oxygen, carbon, fluorine, sulfur, calcium, magnesium, sodium, and zirconium is 100 atomic%. c%.

[0359] As shown in Table 6, in the range from a depth of 4 nm to 5 nm from the surface towards the center of Sample 7 having the second region formed by segregation after the second heating, 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%.

[0360] In addition, when the total amount of lithium, cobalt, oxygen, fluorine, and magnesium is 100%, ​The calculated magnesium concentration was 6.7%, and the calculated fluorine concentration was 1.7%. 。

[0361] Also, the ratio of the magnesium and fluorine concentrations was within the range of Mg:F = y:1 (3 ≤ y ≤ 5), and more precisely, it was about Mg:F = 3.9:1.

[0362] Next, the results of analyzing the bonding state of fluorine in Sample 7 after the second heating by surface XPS analysis are shown in Fig. 39. As a comparative example, the results of a sample prepared in the same manner as Sample 7 except that 10 mol% LiF was used as the additive starting material and magnesium was not added are shown. Also shown are the XPS spectra of the standard samples of MgF2 and LiF.

[0363] As shown in Fig. 39, in the sample using 10 mol% LiF as the additive starting material and not adding magnesium, the peak of the binding energy of fluorine is about 685 eV, which coincides with that of LiF, and it was considered that LiF was the main bonding state of the fluorine present in the surface layer of the positive electrode active material. On the other hand, in Sample 7 using 1 mol% MgO and 2 mol% LiF as the additive starting material and having the second region, the peak of the binding energy of the fluorine present in the surface layer of the positive electrode active material is above 682 eV and less than 685 eV, more precisely 684.3 eV

[0364]

Example

[0364] In this example, when producing a positive electrode active material having a second region formed by segregation, the first The results of examining the temperature of the second heating and the atmosphere during the second heating will be described. .

[0365] <<Temperature of the second heating>> <Preparation of the positive electrode active materials of Samples 11 to 13> Positive electrode active materials of Samples 11 to 13 were prepared while changing the temperature of the second heating. All the starting materials used lithium carbonate and cobalt oxide as common starting materials, and 1 mol% MgO and 2 mol% LiF as additive starting materials.

[0366] Except that the temperature of the second heating was 700 °C for Sample 11, 900 °C for Sample 12, and 1000 °C for Sample 13, the positive electrode active materials were prepared in the same manner as Sample 7 of Example 1. The temperature of the second heating of Sample 7 is 800 °C. The temperature of the second heating of each sample is shown in Table 7.

[0367]

Table 7

[0368] Using the positive electrode active materials of Sample 7 and Samples 11 to 13, secondary batteries were prepared in the same manner as in Example 1, and the cycle characteristics were evaluated. The cycle characteristics of Sample 7 and Samples 11 to 13 are shown in Fig. 40. The charge and discharge conditions were the same as in Example 1.

[0369] Fig. 40(A) is a graph of the energy density during charging at 4.6 V, and Fig. 40(B) is a graph of the energy density retention rate during charging at 4.6 V. As shown in Fig. 40(B), Sample 7 with the second heating temperature of 800 °C showed the best cycle characteristics. Samples 11 with the second heating temperature of 700 °C and 12 with the second heating temperature of 900 °C had the next best cycle characteristics. This was the characteristic. Even in Sample 13 with the second heating temperature set to 1000 °C, after 20 cycles the energy density retention rate was 76%. This is compared with the case of Sample 6 without the added starting material shown in Fig. 26, where the energy density retention rate after 20 cycles was 63%. It can be said that good cycle characteristics were shown.

[0370] From this, it became clear that the temperature of the second heating is preferably 700 °C or higher and 1000 °C or lower, more preferably 700 °C or higher and 9 00 °C or lower, and even more preferably about 800 °C.

[0371] ≪Atmosphere of the second heating≫ <Production of the positive electrode active material of Samples 14 to 16> The positive electrode active materials of Samples 14 to 1 6 were produced with the atmosphere of the second heating changed from dry air to 100% oxygen. All of the starting materials used lithium carbonate and cobalt oxide as the common starting materials, and 1 mol% MgO and 2 mol% LiF as the added starting materials. The positive electrode active materials were produced in the same manner as in Samples 7, 12, and 13, except that the second heating was changed to an oxygen atmosphere.

[0372] Using the positive electrode active materials of Samples 14 to 16, secondary batteries were produced in the same manner as in Example 1, and the cycle characteristics were evaluated together with Samples 7, 12, and 13.

[0373] Graphs of the energy density and cycle characteristics of Samples 7, 12 to 16 are shown in Figs. 41 and 42. Fig. 41 shows the energy density, and Fig. 42 shows the cycle characteristics graph. Figs. 41(A) and 42(A) are for the case where the temperature of the second heating was set to 800 °C. Sample 14 and Sample 7, Figures 41(B) and 42(B) are samples at 900 °C Sample 15 and Sample 12, Figures 41(C) and 42(C) are samples at 1000 °C show the cycle characteristics of Sample 16 and Sample 13. Also, Table 8 shows the atmosphere of the second heating and the temperature of the second heating for each

[0374] [Table 8]

[0375] As shown in Figure 41, when the second heating was performed at 800 °C, 900 °C, and 1000 °C, the second heating showed better cycle characteristics when performed in an oxygen atmosphere than when performed in dry air.

Example

[0376] In this example, the cycle characteristics were compared when magnesium and fluorine were used as the additive starting materials and when elements other than magnesium

[0377] ≪Comparison between Fluorine and Chlorine≫ First, the cycle characteristics were compared when magnesium and fluorine were used as the additive starting materials and when chlorine was used instead of

[0378] <Preparation of Cathode Active Material for Samples 17 and 18> For Sample 7, 1 mol% MgO and 2 mol% LiF were used as the additive starting materials with respect to cobalt. For Sample 17, 1 mol% MgO, 1 mol% LiF, and 1 mol% LiCl were used. For Sample 18, as a comparative example, 1 mol% MgO and 2 mol% It was not added.

[0379] For Sample 7, Sample 17, Sample 18, and Sample 6, the positive electrode active materials were prepared in the same manner as in Example 2, and secondary batteries using them were fabricated and their cycle characteristics were evaluated. The cycle characteristic test was conducted in the same manner as in Example 1.

[0380] <Cycle Characteristics> Table 9 shows the added starting materials for each sample and the energy density retention rates after 20 cycles for each.

[0381]

Table 9

[0382] As shown in Table 9, when chlorine was added instead of fluorine, the cycle characteristics tended to deteriorate. However, Sample 17, which contained 1% each of fluorine and chlorine, had an energy density retention rate of 80% or more after 20 cycles. This was better cycle characteristics compared to Sample 6, which did not contain any of magnesium, fluorine, or chlorine.

[0383] ≪Comparison between Magnesium and Other Metals≫ Next, the cycle characteristics were compared when magnesium and fluorine were used as the added starting materials and when other metals were used instead of magnesium.

[0384] <Fabrication of Positive Electrode Active Materials for Samples 19 to 29> As a sample using magnesium and fluorine as the added starting materials, Sample 7 of Example 1 was used. As a comparative example, Sample 19 used 1 mol% MgO, 1 mol% TiO2, and 2 mol% LiF as the added starting materials. As a comparative example, Sample 20 used 1 m ol% ZrO2 and 2 mol% LiF were used. Sample 21 was used as a comparative example with 1 mo l% TiO2 and 2 mol% LiF. Sample 22 was used as a comparative example with 1 mol % V2O5 and 2 mol% LiF. Sample 23 was used as a comparative example with 1 mol% ZnO and 2 mol% LiF. Sample 24 was used as a comparative example with 1 mol% C aO and 2 mol% LiF. Sample 25 was used as a comparative example with 1 mol% Al2 O3 and 2 mol% LiF. Sample 26 was used as a comparative example with 1 mol% MoO 2 and 2 mol% LiF. Sample 27 was used as a comparative example with 1 mol% SrO, 2 mol% LiF. Sample 28 was used as a comparative example with 1 mol% NaF, 1 m ol% LiF. Sample 29 was used as a comparative example with 1 mol% BaO and 2 mol % LiF. Also, as a comparative example without adding any fluorine or metal, Sample 6 of Example 1 was used.

[0385] For Sample 6, Sample 7, and Samples 19 to 29, the positive electrode active materials were prepared in the same manner as in Example 1, and secondary batteries using them were fabricated and their cycle characteristics were evaluated .

[0386] <Cycle Characteristics> Table 10 shows the added starting materials for each sample and the energy density retention rate after 20 cycles for each .

[0387]

Table 10

[0388] As shown in Table 10, when other metals are added instead of magnesium, the cycle characteristics deteriorate There was a tendency.

[0389] From these results, it became clear that it is extremely effective to use a combination of magnesium and fluorine as the additive starting materials.

[0390] From the previous examples, by adding magnesium and fluorine as the starting materials for the positive electrode active material, it became clear that magnesium segregates on the surface of the positive electrode active material. Also, because it has a good coating layer formed by segregation, it became clear that it becomes a positive electrode active material with high capacity and excellent cycle characteristics.

[0391] Since a secondary battery having such a positive electrode active material has high capacity and long life, it is suitable for portable electronic devices. Furthermore, if it is applied to vehicles such as automobiles, it is also possible to avoid using commercial power sources during peak power demand, and it can also contribute to energy conservation and reduction of carbon dioxide emissions.

Example

[0392] In this example, a positive electrode active material to which nickel, manganese, and cobalt were applied as transition metals in the first region was prepared, and the results of the evaluation will be described.

[0393] <Sample 31, Sample 32> Sample 31 having magnesium and fluorine and Sample 32 having no magnesium and fluorine as a comparative example were prepared.

[0394] Sample 31 was a sample in which 1 atomic% of magnesium and 2 atomic% of fluorine were added to the sum of nickel, manganese, and cobalt as the starting materials. Also, the starting materials ​​​​​​​​​The atomic ratio of nickel, manganese, and cobalt was set to Ni:Mn:Co = 1:1:1.

[0395] First, lithium carbonate (Li2CO3) was used as the lithium source of the common starting materials. Nickel oxide (NiO) was used as the nickel source. Manganese dioxide (MnO2) was used as the manganese source. Cobalt oxide (Co3O4) was used as the cobalt source. Magnesium oxide (MgO) was used as the magnesium source of the added starting materials. Lithium fluoride (LiF) was used as the fluorine source.

[0396] Each starting material was weighed so as to have an atomic ratio of LiCo 0.323 Mn 0.333 Ni 0.333 O2 + MgO 0.01 LiF 0.02

[0397] Next, the weighed starting materials were mixed using a ball mill.

[0398] Next, the mixed starting materials were fired. The firing was carried out at 950 °C for 10 hours, with a heating rate of 200 °C / h, and a flow rate of 10 L / min in a dry atmosphere.

[0399] In the above process, composite oxide particles containing lithium, nickel, manganese, cobalt, magnesium, and fluorine were synthesized.

[0400] The synthesized composite oxide particles were cooled to room temperature.

[0401] Next, the composite oxide particles were heated. The heating was carried out at 800 °C (heating rate: 200 °C / hour) for 2 hours in a dry air atmosphere.

[0402] The heated powder was cooled to room temperature and subjected to a crushing process. The crushing process was carried out by sieving, and a sieve with a mesh opening of 53 μm was used. The particles obtained after the crushing process were used as the positive electrode active material of Sample 31.

[0403]

[0404] Sample 32 was weighed so that the atomic ratio of each starting material was LiCo 0.333 Mn 0.333 Ni 0.333 O2. Also, the firing was carried out at 1000 °C. Otherwise, it was prepared in the same manner as Sample 31.

[0405] The preparation conditions of Sample 31 and Sample 32 are shown in Table 11.

[0406]

[0407] <Cycle characteristics>

[0408]

[0409]

[0410] Next, using the positive electrode active materials of Sample 31 and Sample 32 prepared as described above, a coin-type secondary battery of CR2032 type (diameter 20 mm, height 3.2 mm) was fabricated, and its cycle characteristics were evaluated. For the positive electrode, a slurry obtained by mixing the positive electrode active materials of Sample 31 and Sample 32, acetylene black (AB ) and polyvinylidene fluoride (PVDF) at a ratio of positive electrode active material:AB:PVDF = 95:2.5 :2.5 (weight ratio) was applied to a current collector of aluminum foil. Also, N-methyl-2-pyrrolidone (NMP) was used as the solvent.

[0409] Lithium metal was used for the counter electrode.

[0410] The electrolyte used in the electrolytic solution is 1 mol / L lithium hexafluorophosphate (LiPF6). The electrolyte contains ethylene carbonate (EC) and diethyl carbonate (DEC). C:DEC = 3:7 (volume ratio) was mixed and vinylene carbonate (VC) was added. The material used was one containing 100% by weight of cellulose acetate.

[0411] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0412] The measurement temperature for the cycle characteristic test was 25°C. Charging was performed at a current density of 68 per unit weight of active material. The current density was then increased to 1.4mA / g at a constant current of 0.5mA / g and an upper voltage limit of 4.6V. The battery was charged at a constant voltage up to 1000 kJ / g. The discharge was performed at a constant voltage of 68.5 mA / g. The current was measured at a lower limit voltage of 2.5V.

[0413] The discharge of secondary batteries using the positive electrode active materials of Sample 31 and Sample 32 when charged to 4.6 V The capacitance is shown in FIG. 43(A), and the discharge capacity retention rate is shown in FIG. 43(B).

[0414] Compared with sample 32, which did not contain magnesium and fluoride, Sample 31, to which fluorine was added, showed extremely good cycle characteristics.

[0415] Next, the results of various analyses performed on Sample 31 are shown below.

[0416] <stem-fft> STEM images of the cross-section near the surface of the positive electrode active material of Sample 31 are shown in FIGS. 44 and 45. FIG. 44(B) is an enlarged STEM image of a part of FIG. 44(A). FIGS. 45(A) and 45(B) are enlarged HAADF-STEM images of a part of FIG. 44(A).

[0417] As is apparent from FIG. 45, in the region about 0.5 nm from the surface of the positive electrode active material, a different brightness was observed compared to other regions. This was considered to be because there was a large amount of magnesium, an element lighter than the transition metals. As is apparent from FIG. 45, in the region about 0.5 nm from the surface of the positive electrode active material, a different brightness was observed compared to other regions. This was considered to be because there was a large amount of magnesium, an element lighter than the transition metals. As is apparent from FIG. 45, in the region about 0.5 nm from the surface of the positive electrode active material, a different brightness was observed compared to other regions. This was considered to be because there was a large amount of magnesium, an element lighter than the transition metals.

[0418] Also, in the region from about 0.5 nm to about 5 nm from the surface of the positive electrode active material, a different regularity was observed compared to the internal region. This was considered to be because the crystal orientation was different between the region from about 0.5 nm to about 5 nm from the surface and the region inside that. Also, in the region from about 0.5 nm to about 5 nm from the surface of the positive electrode active material, a different regularity was observed compared to the internal region. This was considered to be because the crystal orientation was different between the region from about 0.5 nm to about 5 nm from the surface and the region inside that. Also, in the region from about 0.5 nm to about 5 nm from the surface of the positive electrode active material, a different regularity was observed compared to the internal region. This was considered to be because the crystal orientation was different between the region from about 0.5 nm to about 5 nm from the surface and the region inside that.

[0419] FIG. 46(A) is a bright-field STEM image of the same range as FIG. 45(B). The FFT (Fast Fourier Transform) image of the region indicated by FFT1 in FIG. 46(A) is FIG. 46(B). As shown in FIG. 46(B) for some of the bright spots in the FFT1 image, they were named A, B, C, and O. image, they were named A, B, C, and O.

[0420] Regarding the bright spots in the FFT image of the region indicated by FFT1, the measured values were: for OA, d = 0.2 2 nm, for OB, d = 0.25 nm, and for OC, d = 0.23 nm. Also, ∠AOB = 5 8°, ∠BOC = 69°, and ∠AOC = 127°.

[0421] This is the data of magnesium oxide (MgO) in the ICDD (International Centre for Diffra ction Data) database (I Obtained from CDD45 - 0945), for OA(200), d = 0.21nm, OB(1 -11), d = 0.24nm, OC(-1 - 11), d = 0.24nm, ∠AOB = 55 °, ∠BOC = 70°, ∠AOC = 125° are close. Therefore, the region shown by FFT1 is a region with a rock - salt - type crystal structure and is presumed to be the image of

[0011] incidence.

[0422] Also, the FFT image of the region shown by FFT2 in Fig. 46(A) is Fig. 46(C). Part of the bright spots of the FFT image is denoted as A, B, C, and O as shown in Fig. 46(C).

[0423] Regarding the bright spots of the FFT image of the region shown by FFT2, the measured values are respectively, for OA, d = 0.2 5nm, for OB, d = 0.21nm, for OC, d = 0.49nm. Also, ∠AOB = 2 6°, ∠BOC = 57°, ∠AOC = 83°.

[0424] This is close to the data of lithium cobalt oxide (LiCoO2) in the ICDD database ( ICDD50 - 0653), for OA(10 - 11), d = 0.24nm, O B(10 - 14), d = 0.20nm, OC(0003), d = 0.47nm, ∠AOB = 25°, ∠BOC = 55°, ∠AOC = 80°. Therefore, the region shown by FFT2 is a region with a layered rock - salt - type crystal structure and is presumed to be the image of [-12 - 10] incidence.

[0425] Also, the FFT image of the region shown by FFT3 in Fig. 46(A) is Fig. 46(D). Part of the bright spots of the FFT3 image is denoted as A, B, C, and O as shown in Fig. 46(D). .

[0426] ​Regarding the bright spots in the FFT image of the region shown by FFT3, the measured values were as follows: for OA, d = 0.2 1 nm, for OB, d = 0.26 nm, and for OC, d = 0.24 nm. Also, ∠AOB = 5 6°, ∠BOC = 72°, and ∠AOC = 128°.

[0427] This is close to the values obtained from the data of lithium cobalt oxide (LiCoO2) in the ICDD database ( ICDD50 - 0653): for OA (01 - 14), d = 0.20 nm, O B (10 - 1 - 2), d = 0.23 nm, OC (1 - 102), d = 0.23 nm, ∠A OB = 55°, ∠BOC = 70°, and ∠AOC = 125°. Therefore, the region shown by FFT2 is inferred to be a region with a layered rock salt - type crystal structure and is the image of [02 - 21] incidence.

[0428] That is, it was clarified that the regions shown by FFT2 and FFT3 have the same layered rock salt - type crystal structure but different crystal axis directions.

[0429] Also, in the observable range of FIGS. 45(A), 45(B), and 46(A), it was observed that the crystal orientations were generally consistent even though the brightness was different.

[0430] Fig. 47 shows the STEM image together with the structure near the surface of the positive electrode active material inferred from the results of STEM - FFT. In Fig. 47, M represents either nickel, manganese, or cobalt.

[0431] FFT3, which is the region inside the positive electrode active material, has a layered rock salt - type crystal structure. Also, it is the image of [02 - 21] incidence where lithium and M atoms overlap and are observed.

[0432] ​​Further, FFT2, which is the region of the surface layer of the positive electrode active material, has a layered rock salt-type crystal structure. Also, in the image of [-12-10] incidence, the repetition of the layer of oxygen atoms, the layer of M (any one of nickel, manganese, and cobalt) atoms, and the layer of lithium atoms can be observed. In the bright-field STEM image, the repetition of the dark and bright layers is considered to be due to the repetition of the layer of M and the layers of oxygen and lithium. That is, FFT3 and FFT2 have the same layered rock salt-type crystal structure, but the directions of the crystal axes are different. Also, FFT1, which is a region closer to the surface than FFT2 in the region of the surface layer of the positive electrode active material, has a rock salt-type crystal structure and is an image of

[0011] incidence.

[0433]

[0434] <edx> Next, the cross section near the surface of the positive electrode active material of Sample 31 was analyzed using EDX. 48 and 49.

[0435] Figure 48(A-1) is a HAADF-STEM image, Figure 48(A-2) is oxygen mapping, 48(B-1) is the mapping of magnesium, and 48(B-2) is the mapping of fluorine. Also, Figure 49(A-1) is the same HAADF-STEM image as Figure 48(A-1), and Figure 49 (A-2) is the manganese mapping, Figure 49 (B-1) is the nickel mapping, Figure 49 (B-2) is the mapping of cobalt.

[0436] First, from Figure 48(B-1), magnesium is distributed in the region of about 3 nm from the surface of the positive electrode active material. It was observed that the particles were being analyzed. From the comparison of -2), it can be seen that there is less manganese in the surface layer of the positive electrode active material than in the interior, and there is less nickel and It was observed that there was a region with a high concentration of cobalt and Zn. This region was about 5 nm from the surface. This region almost overlapped with the region in which a different regularity from the interior was observed in the STEM image.

[0437] Therefore, in sample 31, the positive electrode active material has a region containing magnesium in the surface layer portion, and It was confirmed that the positive electrode active material had a region with a low manganese content in a part of the .

[0438] Taking the above results into consideration, the molar ratio of the starting materials is LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 +1mol%MgO+2mol%LiF, and a sample prepared by heating at 800℃ It was revealed that the positive electrode active material No. 31 has the following characteristics.

[0439] First, in the positive electrode active material of Sample 31, there exists a second region having magnesium oxide in the surface layer portion. Inside, there is a region having LiNi x Mn y Co z O2 (x + y + z = 1) with a layered rock salt-type crystal structure in a portion closer to the center, and a region having LiNi with a layered rock salt-type crystal structure in a portion closer to the surface. a Mn b Co c O2 (a + b + c = 1). It has these.

[0440] The internal LiNi x Mn y Co z O2 and LiNi a Mn b Co c O2 have the same layered rock salt-type crystal structure, but the directions of the crystal axes may be different.

[0441] Also, regarding the content ratios of the respective elements, y > b, and the content ratio of manganese with respect to the sum of nickel, manganese, and cobalt may be low in the region closer to the surface. When the positive electrode active material of Sample 31 having the above characteristics is used in a secondary battery, it exhibits extremely good

[0442] cycle characteristics.

Example

Example

[0443] In this example, the results of analyzing a positive electrode active material prepared by applying cobalt as a transition metal and adding magnesium and fluorine to the starting materials using EELS will be described. For the positive electrode active material prepared using 1 mol% MgO and 2 mol% LiF as the additive starting materials in Example 1. It will be explained.

[0444] Ple 7 was used as the analytical sample for this example.

[0445] The state of cobalt at six analysis points *1 to *6 in the cross section of sample 7 was analyzed by EELS. FIG. 50 shows the vicinity of the surface of the positive electrode active material of Sample 7 used in the EELS analysis. The cross-section of the sample is shown in STEM image. *1 (approximately 1 nm deep from the surface) and *2 (approximately 2.5 nm deep from the surface) are shown in the image. The analysis points are shown as *1 (approximately 5 nm) and *2 (approximately 10 nm) from the surface of the positive electrode active material. m, *5 is approximately 100 nm from the surface of the positive electrode active material, *6 is near the center of the particle of the positive electrode active material .

[0446] The EELS spectrum intensity ratios of the cobalt L2 and L3 levels at each analysis point are shown in Table 1. 2 and Figure 51. The higher the L3 / L2 ratio, the lower the valence of cobalt.

[0447] [Table 12]

[0448] As is clear from Table 12 and Figure 51, the L3 The highest value of L3 / L2 was 4.6. Also, the L3 / L2 from analysis point *2 to analysis point *6 was 4.6. *It was lower than 1 and was within the range of 2.9 to 3.2, so no significant difference was observed.

[0449] From these results, it is clear that at the analysis point*1, cobalt exists in the divalent form as cobalt oxide (CoO). It was estimated that there was a lot of cobalt. It was speculated that most of the cobalt exists in the trivalent form as lithium (LiCoO2). [Explanation of symbols]

[0450] 100 Cathode 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 Lead 212b Lead 214 Separator 215a Junction 215b Junction 217 Fixing member 250 Battery 251 Outer package 261 Bending part 262 Sealing part 263 Sealing part 271 Ridge line 272 Valley line 273 Space 300 Secondary battery 301 Positive electrode can 302 Negative electrode can 303 Gasket 304 Positive electrode 305 Positive electrode current collector 306 Positive electrode active material layer 307 Negative electrode 308 Negative electrode current collector 309 Negative electrode active material layer 310 Separator 500 Secondary battery 501 Positive electrode current collector 502 Positive electrode active material layer 503 Positive electrode 504 Negative electrode current collector 505 Negative electrode active material layer 506 Negative electrode 507 Separator 508 Electrolyte 509 Outer package 510 Positive electrode lead electrode 511 Negative electrode lead electrode 600 Secondary battery 601 Positive electrode cap 602 Battery can 603 Positive terminal 604 Positive electrode 605 Separator 606 Negative electrode 607 Negative terminal 608 Insulating plate 609 Insulating plate 611 PTC element 612 Safety valve mechanism 900 Circuit board 910 Label 911 Terminal 912 Circuit 913 Secondary battery 914 Antenna 915 Seal 916 Layer 917 Layer 918 Antenna 920 Display device 921 Sensor 922 Terminal 930 Housing 930a Housing 930b Housing 931 Negative electrode 932 Positive electrode 933 Separator 950 Wound body 951 Terminal 952 Terminal 980 Secondary battery 993 Wound body 994 Negative electrode 995 Positive electrode 996 Separator 997 Lead electrode 998 Lead electrode 1001 Crystal defect 7100 Portable display device 7101 Housing 7102 Display section 7103 Operation button 7104 Secondary battery 7200 Portable information terminal 7201 Housing 7202 Display section 7203 Band 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 Lead 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 8301 Housing 8302 Refrigerator Door 8303 Freezer Door 8304 Secondary Battery 8400 Automobile 8401 Headlight 8406 Electric Motor 8500 Automobile 8600 Scooter 8601 Side mirror 8602 Secondary battery 8603 Direction indicator 8604 Under-seat storage 9600 Tablet terminal 9625 Switch 9626 Switch 9627 Power switch 9628 Operation switch 9629 Fastener 9630 Housing 9630a Housing 9630b Housing 9631 Display unit 9633 Solar cell 9634 Charge and discharge control circuit 9635 Energy storage element 9636 DCDC converter 9637 Converter 9640 Movable part< / edx> ​​​ < / xps> ​ ​​ < / stem> ​​

Claims

1. Having a positive electrode, The positive electrode has a positive electrode active material, The positive electrode active material has a first region and a second region, The first region has lithium, cobalt, aluminum and oxygen, The second region has magnesium, fluorine and oxygen, The second region covers at least a part of the first region, The second region contains magnesium oxide in which a part of oxygen is substituted with fluorine, A lithium ion secondary battery.

2. Having a positive electrode, The positive electrode has a positive electrode active material, The positive electrode active material has a first region and a second region, The first region has lithium, cobalt, aluminum and oxygen, The second region has magnesium, fluorine and oxygen, The second region covers at least a part of the first region, The positive electrode active material has a peak position of the binding energy of fluorine measured by X-ray photoelectron spectroscopy of 682 eV or more and less than 685 eV, A lithium ion secondary battery.

3. Having a positive electrode, The positive electrode has a positive electrode active material, The positive electrode active material has a first region and a second region, The first region has lithium, cobalt, aluminum and oxygen, The second region has cobalt, magnesium, fluorine and oxygen, The second region covers at least a part of the first region, When the positive electrode active material is analyzed by electron energy loss spectroscopy, with the L2 level of cobalt as L2 and the L3 level of cobalt as L3, the spectral intensity ratio L3 / L2 of cobalt in the first region is less than 3.8, and the spectral intensity ratio L3 / L2 of cobalt in the second region is 3.8 or more, A lithium ion secondary battery.

4. In any one of Claims 1 to 3, Taking the total amount of atoms including lithium, cobalt, oxygen, fluorine and magnesium measured by X-ray photoelectron spectroscopy of the positive electrode active material as 100 atomic%, the magnesium concentration is 1 atomic% or more and 16 atomic% or less, A lithium ion secondary battery.

5. In Claim 1 or Claim 3, The positive electrode active material has a peak position of the binding energy of fluorine measured by X-ray photoelectron spectroscopy of 682 eV or more and less than 685 eV, A lithium ion secondary battery.

6. In any one of Claims 1 to 5, The positive electrode active material has a buffer region between the first region and the second region, The buffer region contains aluminum, a lithium-ion secondary battery. **Claim 7** In any one of Claims 1 to 5, the positive electrode active material has a region that overlaps with the first region and the second region, the overlapping region contains aluminum, a lithium-ion secondary battery.

Images