Manufacturing method for positive electrode active material, and battery

Abstract

To provide a novel positive electrode active material, and a battery with excellent charging and discharging characteristics.SOLUTION: A battery includes a positive electrode. The positive electrode contains lithium cobaltate. The lithium cobaltate contains magnesium, aluminum, and nickel. In XPS analysis of the lithium cobaltate, when the concentration of the cobalt is 1, the concentration of magnesium (Mg / Co) is 0.50 or more and 0.90 or less and the half width of Mg1s peak is 1.0 eV or more and 2.6 eV or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] One aspect of the present invention relates to an object, 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 power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof.

[0002] In the present specification, the electronic device generally refers to all devices having a power storage device, and electro-optical devices having a power storage device, information terminal devices having a power storage device, etc. are all electronic devices.

Background Art

[0003] In recent years, various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries have been actively developed. In particular, lithium-ion secondary batteries with high output and high capacity have rapidly expanded their demand along with the development of the semiconductor industry and have become indispensable in modern information societies as a source of rechargeable energy.

[0004] Among them, for secondary batteries for mobile electronic devices, etc., there is a high demand for secondary batteries with a large discharge capacity per unit weight and excellent cycle characteristics. In order to meet these demands, improvements to the positive electrode active material of secondary batteries have been actively carried out (for example, Patent Document 1 and Patent Document 2). In addition, research on the crystal structure of the positive electrode active material has also been conducted (Non-Patent Documents 1 to 3).

[0005] X-ray Diffraction (XRD) is also one of the techniques used for analyzing the crystal structure of the cathode active material. By using the ICSD (Inorganic Crystal Structure Database) introduced in Non-Patent Document 4, the XRD data can be analyzed. For example, the lattice constant of lithium cobaltate described in Non-Patent Document 5 can be referred to from the ICSD. For the Rietveld method analysis, for example, the analysis program RIETAN-FP (Non-Patent Document 6) can be used. Also, as software for drawing the crystal structure, VESTA (Non-Patent Document 7) can be used.

[0006] Also, as image processing software, for example, ImageJ (Non-Patent Documents 8 to 10) is known. By using this software, for example, the shape of the cathode active material can be analyzed.

[0007] Microelectron diffraction is also effective for identifying the crystal structure of the cathode active material, particularly the crystal structure of the surface layer. For the analysis of the electron diffraction pattern, for example, the analysis program ReciPro (Non-Patent Document 11) can be used. Also, STEM (Scanning Transmission Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy) can be used for elemental analysis of the cathode active material. Non-Patent Document 12 is known as the detection limit (also referred to as the lower detection limit) when using STEM-EDX.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Non-Patent Document 9

Non-Patent Document 10

Non-Patent Document 11

[0010] There is still room for improvement in lithium-ion secondary batteries in various aspects such as output characteristics, discharge capacity, cycle characteristics, reliability, safety, and cost. For example, in order to suppress changes in the crystal structure on the surface of the positive electrode active material, the surface of the positive electrode active material may be coated with an inert oxide, but there is a risk that the insertion and extraction of lithium may be inhibited by the film. When the insertion and extraction of lithium ions are inhibited, a decrease in the discharge capacity during high-rate discharge (also referred to as a decrease in output characteristics or rate characteristics), a decrease in the charge-discharge capacity in a low-temperature environment, and other deteriorations in the characteristics of the secondary battery are a concern.

[0011] Therefore, one aspect of the present invention aims to provide a positive electrode active material that can be used in a lithium-ion secondary battery and promotes the insertion and extraction of lithium ions. Or, one aspect of the problem is to provide a positive electrode active material or a composite oxide in which a decrease in discharge capacity during high-rate discharge is suppressed. Or, one aspect of the problem is to provide a positive electrode active material or a composite oxide in which a decrease in discharge capacity in a low-temperature environment is suppressed. Or, one aspect of the problem is to provide a positive electrode active material or a composite oxide in which a decrease in discharge capacity during charge-discharge cycles is suppressed. Or, one aspect of the problem is to provide a positive electrode active material or a composite oxide whose crystal structure is difficult to collapse even when charge-discharge is repeated. Or, one aspect of the problem is to provide a positive electrode active material or a composite oxide having a large discharge capacity. Or, one aspect of the problem is to provide a secondary battery with high safety or reliability, an electronic device having the secondary battery, or a vehicle having the secondary battery.

[0012] Another aspect of the present invention aims to provide a positive electrode active material, a composite oxide, a power storage device, or a method for producing them.

[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] One aspect of the present invention is a battery having a positive electrode, the positive electrode having lithium cobaltate, the lithium cobaltate having magnesium, aluminum, and nickel, and in the XPS analysis of the lithium cobaltate, when the concentration of cobalt is set to 1, the concentration of magnesium (Mg / Co) is 0.50 or more and 0.90 or less, and in the XPS analysis, the full width at half maximum of the Mg1s peak is 1.0 eV or more and 2.6 eV or less.

[0015] In the above-described battery, when the concentration of magnesium in XPS analysis is set to 1, the concentration of fluorine (F / Mg) is preferably 0.10 or more and 0.20 or less. Further, when the concentration of cobalt in XPS analysis is set to 1, the concentration of aluminum (Al / Co) is preferably 0.01 or more and 0.04 or less, and the concentration of nickel (Ni / Co) is preferably 0.01 or more and 0.07 or less.

[0016] In any one of the above-described batteries, lithium cobaltate having a layered rock salt crystal structure of space group R-3m is used as the positive electrode, lithium metal is used as the negative electrode, and a mixture in which 2 wt% of vinylene carbonate is mixed with lithium hexafluorophosphate, ethylene carbonate, and diethyl carbonate is used as the electrolyte. The current value is set to 0.5C (where 1C = 200 mA / g is satisfied) until a voltage of 4.60 V in a 45°C environment, and then constant voltage charging is performed until the current value becomes 0.05C. When the positive electrode is analyzed by powder X-ray diffraction using CuKα1 line in an argon atmosphere, the XRD pattern preferably has diffraction peaks at at least 2θ = 19.25 ± 0.12° and 2θ = 45.47 ± 0.10°.

[0017] Alternatively, one aspect of the present invention includes a first step of mixing lithium cobaltate and lithium fluoride to produce a first mixture, a second step of heating the first mixture at a temperature of 900°C or higher and 950°C or lower for a time of 2 hours or longer and 10 hours or shorter, a third step of mixing a magnesium source with the first mixture to produce a second mixture, a fourth step of heating the second mixture at a temperature of 850°C or higher and 950°C or lower for a time of 2 hours or longer and 60 hours or shorter, a fifth step of mixing a nickel source and an aluminum source with the second mixture to produce a third mixture, and a sixth step of heating the third mixture at a temperature of 800°C or higher and 900°C or lower for a time of 2 hours or longer and 20 hours or shorter. It is a method for producing a positive electrode active material.

[0018] In the method for producing the above-described positive electrode active material, when performing EELS analysis on a portion within 2 nm from the surface of the first mixture that has undergone the second step, the valence of cobalt is preferably 2.35 or more and 2.90 or less.

[0019] Alternatively, in the method for producing the above-described positive electrode active material, in the third step, it is preferable to mix lithium fluoride in addition to the magnesium source.

[0020] In any one of the above-described methods for producing a positive electrode active material, in the third step, when using magnesium fluoride as the magnesium source and setting the number of moles of lithium cobaltate to 100, it is preferably mixed so that the number of moles of magnesium fluoride is 0.5 or more and 3.0 or less.

[0021] Also, in the method for producing the above-described positive electrode active material, in the fifth step, it is preferable to use nickel hydroxide as the nickel source and aluminum hydroxide as the aluminum source. Further, when the number of moles of lithium cobaltate is 100, it is preferably mixed so that the number of moles of nickel hydroxide is 0.05 or more and 4.0 or less, and the number of moles of aluminum hydroxide is 0.05 or more and 4.0 or less.

Advantages of the Invention

[0022] According to one aspect of the present invention, it is possible to provide a positive electrode active material that can be used in a lithium-ion secondary battery and promotes the insertion and extraction of lithium ions. Or, it is possible to provide a positive electrode active material or a composite oxide in which a decrease in discharge capacity during high-rate discharge is suppressed. Or, it is possible to provide a positive electrode active material or a composite oxide in which a decrease in discharge capacity in a low-temperature environment is suppressed. Or, it is possible to provide a positive electrode active material or a composite oxide in which a decrease in discharge capacity during charge-discharge cycles is suppressed. Or, it is possible to provide a positive electrode active material or a composite oxide whose crystal structure is difficult to collapse even when charge-discharge is repeated. Or, it is possible to provide a positive electrode active material or a composite oxide having a large discharge capacity. Or, it is possible to provide a secondary battery with high safety or reliability, an electronic device having the secondary battery, or a vehicle having the secondary battery.

[0023] Also, according to one aspect of the present invention, it is possible to provide a positive electrode active material, a composite oxide, an energy storage device, or a method for producing them.

[0024] Note that the description of these effects does not prevent the existence of other effects. Note that one aspect of the present invention does not necessarily have to have all of these effects. Note that other effects will be obvious from the description in the specification, drawings, claims, etc., and it is possible to extract these other effects from the description in the specification, drawings, claims, etc.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

Figure 34

Figure 35

Figure 36

Figure 37

Figure 38

Figure 39

Figure 40

Figure 41

Figure 42

Figure 43

Figure 44

Figure 45

Figure 46

Figure 47

Figure 48

Embodiments for Carrying Out the Invention

[0026] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings and the like. However, the present invention is not construed as being limited to the following embodiments. It is possible to change the embodiments for carrying out the invention without departing from the gist of the present invention.

[0027] In this specification and the like, the space group is represented using the Short notation of the international notation (or Hermann-Mauguin symbol). Also, the crystal plane and crystal direction are represented using Miller indices. In crystallography, the notations of the space group, crystal plane, and crystal direction are represented by numbers with a bar on top, but in this specification and the like, due to formatting constraints, instead of putting a bar on top of the number, a -(minus sign) may be attached before the number for expression. Also, the individual orientation indicating the direction within the crystal is represented by [ ], the set orientation indicating all equivalent directions is represented by < >, the individual plane indicating the crystal plane is represented by ( ), and the set plane having equivalent symmetry is represented by {}, respectively. Also, the trigonal crystal represented by the space group R-3m is generally represented by a composite hexagonal lattice of a hexagonal crystal for easier understanding of the structure, and in this specification and the like, unless otherwise specified, the space group R-3m will be represented by a composite hexagonal lattice. Also, (hkil) may be used as the Miller index in addition to (hkl). Here, i is -(h + k).

[0028] Note that in this specification and the like, the particle is not limited to only referring to a spherical shape (circular cross-sectional shape), and examples of the cross-sectional shape of each particle include an elliptical shape, a rectangular shape, a trapezoidal shape, a triangular shape, a quadrangular shape with rounded corners, an asymmetric shape, etc., and furthermore, each particle may be amorphous.

[0029] The theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium in the positive electrode active material has been removed. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 275 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0030] Also, the degree to which insertable and removable lithium remains in the positive electrode active material is indicated by x in the composition formula, for example, Li x in MO2. Here, M represents a transition metal, and in this specification and the like, unless otherwise specified, M is cobalt and / or nickel. In the case of the positive electrode active material in a lithium-ion secondary battery, x = (theoretical capacity - charged capacity) / theoretical capacity can be used. For example, when a lithium-ion secondary battery using Li x MO2 as the positive electrode active material is charged to 219.2 mAh / g, Li 0.2 MO2 or x = 0.2 can be stated. When x in Li x MO2 is small, for example, it means 0.1 < x ≤ 0.24.

[0031] When properly synthesized lithium cobaltate before being used in the positive electrode approximately satisfies the stoichiometric ratio, it is LiCoO2 and x = 1. Also, the lithium cobaltate contained in the lithium-ion secondary battery in the state where discharge has ended can also be said to be LiCoO2 and x = 1. The state where discharge has ended (discharged state) mentioned here refers to, for example, a state where the current is 100 mA / g or less and the voltage becomes 3.0 V or 2.5 V or less.

[0032] Li x The charged capacity and / or discharged capacity used for calculating x in Li

[0033] Also, the space group of the positive electrode active material and the like is identified by XRD, electron diffraction, neutron diffraction, or the like. Therefore, in this specification and the like, belonging to a certain space group, being a member of a certain space group, or being a certain space group can be paraphrased as being identified as a certain space group.

[0034] Also, if the anions have a structure in which three layers are stacked with each other shifted like ABCABC, it shall be called a cubic close-packed structure. Therefore, the anions do not necessarily have to be a strict cubic lattice. At the same time, since real crystals always have defects, the analysis results do not necessarily have to be as per the theory. For example, in an FFT (Fast Fourier Transform) pattern such as an electron diffraction pattern or a TEM (Transmission Electron Microscope) image, spots may appear at positions slightly different from the theoretical positions. For example, if the deviation in orientation from the theoretical position is 5° or less, or 2.5° or less, it can be said that it has a cubic close-packed structure.

[0035] Also, the distribution of a certain element shall refer to a region where the element is continuously detected within a range that is not noise by a certain continuous analysis method. The region where it is continuously detected within a range that is not noise can also be said to be a region that is always detected when the analysis is performed multiple times, for example.

[0036] In this specification and the like, the positive electrode active material may be expressed as a composite oxide, a positive electrode material, a positive electrode material, a positive electrode material for a secondary battery, a positive electrode material for a lithium ion secondary battery, or the like.

[0037] Also, when describing the characteristics of individual particles of the positive electrode active material in the following embodiments and the like, not all particles necessarily have to have those characteristics. For example, if 50% or more, preferably 70% or more, more preferably 90% or more of randomly selected three or more particles of the positive electrode active material have those characteristics, it can be said that there is a sufficient effect of improving the characteristics of the positive electrode active material and the secondary battery having the same.

[0038] Unless otherwise specified, the materials of the secondary battery (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) shall be described in the state before deterioration. It is assumed that the reduction in discharge capacity due to the aging process and burn-in process during the secondary battery manufacturing stage is not considered deterioration. For example, when the discharge capacity of a secondary battery, which is a single cell or a battery pack, is 97% or more of the rated capacity, it can be said to be in the state before deterioration. The rated capacity conforms to JIS C 8711:2019 in the case of secondary batteries for portable devices. In the case of other secondary batteries, it conforms to each JIS, IEC standard, etc. for electric vehicle propulsion, industrial use, etc., not limited to the above JIS standard.

[0039] In this specification and the like, the state of the materials of the secondary battery before deterioration may be referred to as the initial product or the initial state, and the state after deterioration (the state when the discharge capacity is less than 97% of the rated capacity of the secondary battery) may be referred to as the in-use product or the in-use state, or the used product or the used state.

[0040] In this specification and the like, the (001) plane, the (003) plane, etc. may be collectively referred to as the (00l) plane. In this specification and the like, the (00l) plane may be referred to as the C plane, the basal plane, etc. Also, in lithium cobalt oxide, lithium has a two-dimensional diffusion path. That is, it can be said that the diffusion path of lithium exists along the plane. In this specification and the like, a plane other than the plane where the diffusion path of lithium is exposed, that is, a plane other than the plane where lithium is inserted and removed (specifically, the (00l) plane), may be referred to as the edge plane.

[0041] In this specification and the like, secondary particles refer to particles formed by the aggregation of primary particles. Also, in this specification and the like, primary particles refer to particles that do not have grain boundaries on their appearance. Also, in this specification and the like, single particles refer to particles that do not have grain boundaries on their appearance. Also, in this specification and the like, single crystals refer to crystals in a state where there are no grain boundaries inside the particles, and polycrystals refer to crystals in a state where there are grain boundaries inside the particles. Polycrystals may also be referred to as an aggregate of a plurality of crystallites, and a grain boundary may also be referred to as an interface existing between two or more crystallites. Note that in polycrystals, the orientations of the crystallites may be aligned.

[0042] In this specification and the like, there may be a description of "A and / or B", which is an example of a description when including only A, only B, or both A and B.

[0043] A short circuit in a secondary battery not only causes problems in the charging operation and / or discharging operation of the secondary battery, but also may lead to heat generation and ignition. In order to realize a safe secondary battery, it is preferable that a short circuit is suppressed even at a high charging voltage. The positive electrode of a battery according to one aspect of the present invention suppresses a short circuit even at a high charging voltage. Therefore, a battery can be achieved that achieves both a high discharge capacity and safety.

[0044] (Embodiment 1) In this embodiment, an example of a method for producing the positive electrode active material 100, which is the positive electrode active material of a battery according to one aspect of the present invention, will be described. FIGS. 1(A) to 3(C) are diagrams for explaining the method for producing the positive electrode active material 100.

[0045] In order to produce the positive electrode active material 100, the way of adding the additive elements is important. At the same time, it is also important that the crystallinity inside the positive electrode active material is good.

[0046] Therefore, in the manufacturing process of the positive electrode active material 100, first, a first lithium source and a cobalt source are mixed and heat-treated to synthesize lithium cobaltate. Next, it is preferable to mix the lithium cobaltate and a second lithium source and perform heat treatment, and then mix an additive element source and perform heat treatment.

[0047] In a method of synthesizing lithium cobaltate having an additive element by mixing the additive element source simultaneously with the first lithium source and the cobalt source, it is difficult to increase the concentration of the additive element in the surface layer portion of the positive electrode active material. Further, if heating is not performed only by mixing the additive element source after synthesizing lithium cobaltate, the additive element only adheres without solid-solubilizing in lithium cobaltate. It is difficult to distribute the additive element well without sufficient heating. Therefore, it is preferable to mix the additive element source after synthesizing lithium cobaltate and perform heat treatment.

[0048] However, if the heat treatment temperature is too high, cation mixing may occur and an additive element, for example, magnesium, may enter the cobalt site more likely. Magnesium present in the cobalt site has no effect of maintaining the R-3m layered rock salt type crystal structure when x in Li x CoO2 is small. Further, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium being evaporated.

[0049] 〔Initial heating〕 Therefore, it is preferable to mix and heat (also referred to as initial heating) with the second lithium source before mixing and heating with the additive element source. Here, as the second lithium source, it is preferable to use a material that functions as a flux, for example, lithium fluoride is suitable.

[0050] Further, it is preferable to mix the lithium cobaltate and the second lithium source sufficiently. As a mixing method, for example, it can be mixed by a ball mill.

[0051] In the step of sufficiently mixing lithium cobaltate and a second lithium source, there is an effect of eliminating the adhesion between the particles of lithium cobaltate.

[0052] Furthermore, by adding a material that functions as a flux as the second lithium source, when mixing and heating lithium cobaltate after initial heating and an additive element source in subsequent steps, there is an effect of suppressing the re - adhesion between the particles of lithium cobaltate.

[0053] If the additive element is added and heated in a state where the particles of lithium cobaltate are adhered to each other, there is a risk that the additive element may not be sufficiently distributed in the adhered part. Therefore, when the adhesion is eliminated in a subsequent step, for example, in a pressing step after coating on a positive electrode current collector, a surface with insufficient additive element may be exposed, and there is a risk of deterioration starting from that surface when used in a secondary battery. Therefore, it is preferable to suppress the adhesion between the particles of lithium cobaltate by the method as described above and then mix and heat the additive element source.

[0054] Also, by adding a flux in the step of initial heating, when mixing and heating lithium cobaltate after initial heating and an additive element source in subsequent steps, a melting point drop occurs near the surface of lithium cobaltate. By lowering the melting point in this way, it becomes easy to distribute the additive element well at a temperature at which cation mixing is less likely to occur.

[0055] Therefore, the heating temperature in the initial heating is preferably a temperature equal to or higher than the melting point of the second lithium source. For example, when using lithium fluoride as the second lithium source, it is preferably a temperature higher than the melting point of lithium fluoride, which is 848 °C (for example, 850 °C or higher), and more preferably 900 °C or higher. Also, the heating temperature in the initial heating is preferably equal to or lower than the temperature at which lithium cobaltate is synthesized (for example, 950 °C or lower). That is, as the initial heating, it is preferable to mix lithium cobaltate and lithium fluoride and heat at a temperature of 900 °C or higher and 950 °C or lower.

[0056] Moreover, by using lithium cobaltate that has undergone the above-described initial heating, it is possible to suppress lithium deficiency generated by the evaporation of lithium in the process of mixing and heating subsequent additive elements.

[0057] The lithium cobaltate that has undergone the above-described initial heating preferably has a larger abundance ratio of the layered rock salt-type crystal structure in the surface layer portion compared to lithium cobaltate before the initial heating. For example, in the lithium cobaltate that has undergone the above-described initial heating, for the portion within 2 nm from the surface, the layered rock salt-type crystal structure is preferably 35% or more, more preferably 45% or more. Also, when performing EELS analysis, the valence of cobalt is preferably 2.35 or more, more preferably 2.45 or more. The presence of a large amount of the layered rock salt-type crystal structure is one factor indicating that lithium deficiency is suppressed.

[0058] On the other hand, it is preferable that not all of the surface layer portion of lithium cobaltate has a layered rock salt-type crystal structure. For example, in pure lithium cobaltate, the solid solubility limit of magnesium is extremely low. In order to dissolve additive elements such as magnesium at a sufficient concentration, it is preferable that the surface layer portion of lithium cobaltate also has the characteristics of the rock salt-type crystal structure. Therefore, in the lithium cobaltate that has undergone the above-described initial heating, for the portion within 2 nm from the surface, the layered rock salt-type crystal structure is preferably less than 100%, more preferably 90% or less. Also, when performing EELS analysis, the valence of cobalt is preferably less than 3.00, more preferably 2.90 or less.

[0059] That is, in the lithium cobaltate that has undergone the above-described initial heating, for the portion within 2 nm from the surface, the layered rock salt-type crystal structure is preferably 35% or more and less than 100%, more preferably 35% or more and 90% or less, and even more preferably 45% or more and 90% or less. Also, when performing EELS analysis, the valence of cobalt is preferably 2.35 or more and less than 3.00, more preferably 2.35 or more and 2.90 or less, and even more preferably 2.45 or more and 2.90 or less.

[0060] Method 1 for Preparing Cathode Active Material 100 Method 1 for preparing the cathode active material 100 through heat treatment and initial heating will be described with reference to FIGS. 1(A) to 1(D).

[0061] <Step S11> In step S11 shown in FIG. 1(B), as the starting materials, a first lithium source (Li source 1) and a cobalt source (Co source) are prepared as the first lithium and transition metal materials, respectively.

[0062] As the first lithium source, it is preferable to use a lithium-containing compound. For example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium fluoride, etc. can be used. The lithium source preferably has a high purity. For example, a material with a purity of 99.99% or more can be used.

[0063] As the cobalt source, it is preferable to use a cobalt-containing compound. For example, cobalt tetroxide, cobalt hydroxide, etc. can be used.

[0064] The cobalt source preferably has a high purity. For example, a material with a purity of 3N (99.9%) or more, preferably 4N (99.99%) or more, more preferably 4N5 (99.995%) or more, and even more preferably 5N (99.999%) or more can be used. By using a high-purity material, the impurities of the cathode active material can be controlled. As a result, the capacity of the secondary battery increases and / or the reliability of the secondary battery improves.

[0065] In addition, it is preferable that the cobalt source has high crystallinity, for example, it preferably has single crystal grains. As the evaluation of the crystallinity of the cobalt source, there are evaluations by TEM images, STEM images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, etc., or evaluations by X-ray diffraction, electron diffraction, neutron diffraction, etc. Note that the above-described methods for evaluating crystallinity can be applied not only to cobalt sources but also to the evaluation of other crystallinity.

[0066] <Step S12> Next, as Step S12 shown in Fig. 1(B), the first lithium source and the cobalt source are pulverized and mixed to produce a mixed material. The pulverization and mixing can be performed either dry or wet. The wet method can pulverize and mix the particles more finely. When performing wet, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that hardly reacts with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or more is used. It is preferable to mix the first lithium source and the cobalt source in dehydrated acetone with a purity of 99.5% or more and the water content suppressed to 10 ppm or less, and then perform pulverization and mixing. By using dehydrated acetone with the above purity, impurities that may be mixed in can be reduced.

[0067] As the means for pulverization and mixing, a ball mill, a bead mill, or the like can be used. When using a ball mill, it is preferable to use aluminum oxide balls or zirconium oxide balls as the pulverization media. Zirconium oxide balls are preferable because they discharge less impurities. Also, when using a ball mill, a bead mill, or the like, in order to suppress contamination from the media, it is preferable that the peripheral speed be 100 mm / s or more and 2000 mm / s or less. In this embodiment, it is carried out with a peripheral speed of 838 mm / s (rotation speed 400 rpm, diameter of the ball mill 40 mm).

[0068] <Step S13> Next, as shown in Step S13 in Fig. 1(B), the above-mentioned mixed material is heated. The heating is preferably carried out at 800°C or more and 1100°C or less, more preferably at 900°C or more and 1050°C or less, and even more preferably about 900°C. If the temperature is too low, there is a possibility that the decomposition and melting of the first lithium source and cobalt source will be insufficient. On the other hand, if the temperature is too high, lithium may evaporate from the first lithium source and / or cobalt may be excessively reduced, etc., which may cause defects. For example, cobalt may change from trivalent to divalent, and oxygen defects may be induced.

[0069] If the heating time is too short, lithium cobaltate will not be synthesized, but if it is too long, the productivity will decrease. For example, the heating time is preferably 1 hour or more and 100 hours or less, and more preferably 2 hours or more and 20 hours or less.

[0070] The heating rate depends on the temperature reached by the heating temperature, but is preferably 80°C / h or more and 250°C / h or less. For example, when heating at 1000°C for 10 hours, the heating rate can be 200°C / h.

[0071] Heating is preferably carried out in an atmosphere with little water such as dry air. For example, an atmosphere with a dew point of -50°C or lower, more preferably -80°C or lower, is good. In this embodiment, heating will be carried out in an atmosphere with a dew point of -93°C. Also, in order to suppress impurities that may be mixed into the material, it is preferable that the impurity concentrations of CH4, CO, CO2, H2, etc. in the heating atmosphere are each 5 ppb (parts per billion) or less.

[0072] An atmosphere having oxygen is preferable as the heating atmosphere. For example, there is a method of continuously introducing dry air into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method of continuously introducing oxygen into the reaction chamber and having the oxygen flow through the reaction chamber is called a flow.

[0073] When the heating atmosphere is an atmosphere having oxygen, a method without flowing may also be used. For example, a method of evacuating the reaction chamber and then filling it with oxygen (which may also be called purging) so that the oxygen does not enter or leave the reaction chamber may be used. For example, the reaction chamber may be evacuated to -970 hPa and then filled with oxygen up to 50 hPa.

[0074] Cooling after heating may be natural air cooling, but it is preferable that the temperature drop time from the specified temperature to room temperature is within 10 hours to 50 hours. However, it is not necessarily required to cool to room temperature, and it may be cooled to the temperature allowed by the next step.

[0075] Heating in this step may be carried out by a rotary kiln or a roller hearth kiln. Heating by a rotary kiln can be carried out with stirring in either a continuous or batch mode.

[0076] When heating, the container for accommodating the object to be heated is preferably an alumina crucible or an alumina setter (also called a sheath). The alumina crucible is a material with almost no impurities mixed in. In this embodiment, a setter made of alumina with a purity of 99.9% is used. Note that it is preferable to cover the crucible or the setter with a lid before heating to prevent the volatilization of the material. Also, mullite-cordierite may be used as the material of the crucible and the setter.

[0077] Also, it is preferable to use a used crucible rather than a new one. In this specification and the like, a new crucible refers to one that has been heated with a material containing lithium, transition metal M, and / or additive element no more than twice. Also, a used crucible refers to one that has undergone the process of heating with a material containing lithium, transition metal M, and / or additive element three or more times. This is because when using a new crucible, there is a risk that a part of the material such as lithium fluoride will be absorbed, diffused, moved, and / or adhered to the sheath during heating. When a part of the material is lost due to these, the concern that the element distribution in the surface layer part of the positive electrode active material will not be in a preferable range increases. On the other hand, this risk is less with a used crucible.

[0078] After heating, it may be crushed as necessary and further sieved. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. Also, it is preferable to use a zirconia mortar as the mortar. The zirconia mortar is a material that is less likely to release impurities. Specifically, a zirconia mortar with a purity of 90% or more, preferably 99% or more, is used. Note that in the heating processes described later other than step S13, heating conditions equivalent to those in step S13 can be applied.

[0079] <Step S14> Through the above steps, lithium cobalt oxide (LiCoO2) shown in step S14 in Fig. 1(B) can be synthesized.

[0080] Although an example of producing lithium cobaltate by a solid-phase method as in Steps S11 to S14 has been shown, lithium cobaltate may be produced by a coprecipitation method. Further, lithium cobaltate may be produced by a hydrothermal method.

[0081] <Step S15> In Step S15 shown in FIG. 1(A), a second lithium source (Li source 2) is prepared. As the second lithium source, it is preferable to use, for example, lithium fluoride.

[0082] <Step S16> Next, in Step S16 shown in FIG. 1(A), lithium cobaltate and the second lithium source are mixed. The mixing in Step S16 is preferably carried out under milder conditions than the mixing in Step S12 so as not to destroy the shape of the lithium cobaltate particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in Step S12. Also, it can be said that the dry method is milder than the wet method. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use, for example, zirconium oxide balls as the media.

[0083] <Step S17> Next, as Step S17 shown in FIG. 1(A), the mixture of lithium cobaltate and the second lithium source is heated. The heating is preferably carried out at 800°C or higher and 1000°C or lower, more preferably at 850°C or higher and 950°C or lower, and still more preferably at 900°C or higher and 950°C or lower. The heating time is preferably 1 hour or more and 60 hours or less, more preferably 2 hours or more and 20 hours or less, still more preferably 2 hours or more and 10 hours or less, and still more preferably 2 hours or more and 6 hours or less. For the first heating of lithium cobaltate, the heating in Step S17 may be called initial heating. Or since it is heated before Step S33 shown below, it may be called preheating or pretreatment. By carrying out Step S16 and Step S17, lithium cobaltate with a smooth surface can be obtained.

[0084] Note that lithium cobaltate synthesized in advance may be used in step S14. In this case, steps S11 to S13 can be omitted. Even when lithium cobaltate synthesized in advance is used, by performing steps S16 and S17, lithium cobaltate with a smooth surface can be obtained.

[0085] <Step S20> Next, as shown in step S20, it is preferable to add element A to the lithium cobaltate that has undergone initial heating. When element A is added to the lithium cobaltate that has undergone initial heating, element A can be added evenly. Therefore, the order of adding element A after initial heating is preferable. The step of adding element A will be described with reference to FIGS. 1(C) and 1(D).

[0086] <Steps S21 to S23> Using FIG. 1(C), the steps of preparing the element A source (A source) will be described respectively. A lithium source may be prepared together with the element A source.

[0087] As element A, one or more selected from the elements described in the previous embodiment, for example, magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. Also, one or two selected from bromine and beryllium can be used.

[0088] <Step S21> The step S21 shown in FIG. 1(C) will be described. When magnesium is selected as the element to be added, the element A source can be called a magnesium source (Mg source). As the magnesium source, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, or the like can be used. Also, a plurality of the above-described magnesium sources may be used.

[0089] When fluorine is selected as the additive element, the additive element source can be referred to as a fluorine source (F source). As the fluorine source, for example, lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF3, CeF4), lanthanum fluoride (LaF3), or sodium hexafluoroaluminate (Na3AlF6) can be used. Among them, lithium fluoride is preferable because its melting point is relatively low at 848°C and it is easily melted in the heating process described later. When lithium fluoride is used as the fluorine source, the lithium fluoride can also be referred to as a third lithium source.

[0090] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Also, lithium fluoride can be used as a lithium source. Another lithium source used in step S21 is lithium carbonate.

[0091] Also, as the fluorine source, gases such as fluorine (F2), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O5F2, O6F2, O2F) can be used and mixed into the atmosphere in the heating process described later. Also, a plurality of the above-mentioned fluorine sources can be used.

[0092] In this embodiment, lithium fluoride (LiF) is prepared as a fluorine source, and magnesium fluoride (MgF2) is prepared as a fluorine source and a magnesium source. When lithium fluoride and magnesium fluoride are mixed at about LiF:MgF2 = 65:35 (molar ratio), the effect of lowering the melting point is the highest. On the other hand, if the amount of lithium fluoride increases, there is a concern that lithium becomes excessive and the cycle characteristics deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is preferably LiF:MgF2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF2 = x:1 (x = 0.33 or in the vicinity thereof). In this specification and the like, the vicinity means a value greater than 0.9 times and less than 1.1 times that value.

[0093] <Step S22> Next, in step S22 shown in FIG. 1(C), the magnesium source and the fluorine source are pulverized and mixed. This step can be carried out by selecting from the pulverization and mixing conditions described in step S12.

[0094] <Step S23> Next, in step S23 shown in FIG. 1(C), the material pulverized and mixed above can be recovered to obtain an additive element A source (A source). Note that the additive element A source shown in step S23 has a plurality of starting materials and can be called a mixture.

[0095] The particle size of the above mixture preferably has a D50 (median diameter) of 600 nm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less. Even when one kind of material is used as the additive element source, the D50 (median diameter) is preferably 600 nm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less.

[0096] When such a micronized mixture (including the case where there is one kind of additive element) is used, when it is mixed with lithium cobaltate in a subsequent process, it is easy to uniformly adhere the mixture to the surface of the lithium cobaltate particles. When the mixture is uniformly adhered to the surface of the lithium cobaltate particles, it is preferable because it is easy to distribute or diffuse the additive element evenly in the surface layer portion of the positive electrode active material 100 after heating.

[0097] <Step S21> A process different from that in Fig. 1(C) will be described with reference to Fig. 1(D). In step S21 shown in Fig. 1(D), four kinds of additive element sources to be added to lithium cobaltate are prepared. That is, Fig. 1(D) is different from Fig. 1(C) in the types of additive element sources. A lithium source may be prepared together with the additive element source.

[0098] As the four kinds of additive element sources, a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source) are prepared. Note that the magnesium source and the fluorine source can be selected from the compounds and the like described in Fig. 1(C). As the nickel source, nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0099] <Steps S22 and S23> Steps S22 and S23 shown in Fig. 1(D) are the same as the steps described in Fig. 1(C).

[0100] <Step S31> Next, in step S31 shown in Fig. 1(A), lithium cobaltate that has undergone initial heating and an additive element A source (A source) are mixed.

[0101] In the present embodiment, the number of magnesium atoms contained in the additive element A source is preferably 0.50% or more and 3.0% or less, more preferably 0.75% or more and 2.0% or less, and even more preferably 0.75% or more and 1.0% or less with respect to the number of cobalt atoms of the lithium cobaltate.

[0102] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 so as not to break the shape of the lithium cobaltate particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, it can be said that the dry condition is milder than the wet condition. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconium oxide balls as media, for example.

[0103] In this embodiment, mixing is carried out dry for 1 hour at 150 rpm using a ball mill with zirconium oxide balls having a diameter of 1 mm. Also, the mixing is to be carried out in a dry room where the dew point is -100°C or higher and -10°C or lower.

[0104] <Step S32> Next, in step S32 of FIG. 1(A), the material mixed above is recovered to obtain a mixture 903. When recovering, sieving may be carried out as necessary.

[0105] In FIGS. 1(A) to 1(D), a manufacturing method of adding additive elements only after passing through initial heating is described, but the present invention is not limited to the above method. The additive elements may be added at other timings, or may be added multiple times. The timing may be changed depending on the element.

[0106] <Step S33> Next, in step S33 shown in FIG. 1(A), the mixture 903 is heated.

[0107] For example, when MgF2 is included as the additive element source A, since the eutectic point of LiF and MgF2 is around 742°C, the heating temperature in step S33 is preferably 742°C or higher.

[0108] In addition, since an endothermic peak is observed at around 830°C in the differential scanning calorimetry (DSC test) for the mixture obtained by mixing so that LiCoO2:LiF:MgF2 = 100:0.33:1 (molar ratio), a heating temperature of 830°C or higher is more preferable. Therefore, the heating in step S33 is preferably performed at 800°C or higher and 1000°C or lower, more preferably at 830°C or higher and 950°C or lower, and even more preferably at 850°C or higher and 950°C or lower. Also, the heating time is preferably 1 hour or more and 60 hours or less, and more preferably 2 hours or more and 20 hours or less.

[0109] In the manufacturing method described in this embodiment, LiF, which is the second lithium source added in steps S16 and S17 of FIG. 1(A), may function as a flux. Due to this function, the heating temperature in step S33 can be lowered to less than the decomposition temperature of lithium cobaltate, for example, 742°C or higher and 950°C or lower, and an additive element such as magnesium can be present in the surface layer portion, and a positive electrode active material with good characteristics can be produced.

[0110] Supplement regarding the heating time. The heating time varies depending on conditions such as the heating temperature, the size of lithium cobaltate in step S14, and the composition. When lithium cobaltate is small, a lower heating temperature or a shorter heating time may be more preferable than when it is large.

[0111] <Step S34> Next, in step S34 shown in FIG. 1(A), the heated material is recovered to obtain the positive electrode active material 100. At this time, the recovered particles can be crushed by sieving them if necessary. Through the above steps, the positive electrode active material 100 of one aspect of the present invention can be produced. The surface of the positive electrode active material of one aspect of the present invention is smooth.

[0112] 《Manufacturing Method 2 of Positive Electrode Active Material 100》 Next, a method 2 for producing the positive electrode active material 100, which is a different form of implementing the present invention from the method 1 for producing the positive electrode active material 100, will be described with reference to FIGS. 2 to 3(C). The method 2 for producing the positive electrode active material mainly differs from the method 1 in the number of times of adding the additive elements and the mixing method. Other descriptions can refer to the descriptions of the method 1.

[0113] In FIG. 2, steps S11 to S17 are performed in the same manner as in FIGS. 1(A) and 1(B), and lithium cobaltate that has undergone initial heating is prepared.

[0114] <Step S20a> Next, as shown in step S20a, it is preferable to add the additive element A1 to the lithium cobaltate that has undergone initial heating.

[0115] <Step S21> In steps S21 to S23 shown in FIG. 3(A), a first additive element source (A1 source) is prepared. As the first additive element source, it can be selected and used from the additive elements A described in step S21 shown in FIG. 1(C). For example, as the additive element A1, any one or more selected from magnesium, fluorine, and calcium can be preferably used. FIG. 3(A) exemplifies the case where a magnesium source (Mg source) and a fluorine source (F source) are used as the first additive element source.

[0116] Steps S21 to S23 shown in FIG. 3(A) can be performed under the same conditions as steps S21 to S23 shown in FIG. 1(C). As a result, the additive element source (A1 source) can be obtained in step S23.

[0117] Also, steps S31 to S33 shown in FIG. 2 can be performed in the same process as steps S31 to S33 shown in FIG. 1(A).

[0118] <Step S34a> Next, the material heated in step S33 is recovered to produce lithium cobaltate having the additive element A1. To distinguish it from the lithium cobaltate in step S14, it is called a composite oxide.

[0119] <Step S40> In step S40 shown in FIG. 2, a second additive element source (A2 source) is prepared. This will be described with reference to FIGS. 3(B) and 3(C) as well.

[0120] <Step S41> In steps S41 to S43 shown in FIG. 3(B), a second additive element source (A2 source) is prepared. As the additive element A2 included in the second additive element source, it can be selected and used from among the additive elements A described in step S21 shown in FIG. 1(D). For example, as the additive element A2, any one or more selected from nickel, boron, zirconium, and aluminum can be preferably used. FIG. 3(B) exemplifies the case where a nickel source (Ni source) and an aluminum source (Al source) are used as the second additive element source. As the nickel source, for example, nickel hydroxide, nickel fluoride, etc. can be used. Also, as the aluminum source, for example, aluminum hydroxide, aluminum fluoride, etc. can be used.

[0121] The atomic number of nickel contained in the second additive element source (A2 source) is preferably 0.05% or more and 4.0% or less, more preferably 0.20% or more and 2.0% or less, and even more preferably 0.20% or more and 1.0% or less with respect to the atomic number of cobalt that the lithium cobaltate has. For example, when nickel hydroxide is used as the nickel source, when the number of moles of lithium cobaltate in step S10 is 100, the number of moles of nickel hydroxide contained in the second additive element source is preferably 0.05 or more and 4.0 or less (0.05 mol% or more and 4.0 mol% or less), more preferably 0.20 or more and 2.0 or less (0.20 mol% or more and 2.0 mol% or less), and even more preferably 0.20 or more and 1.0 or less (0.20 mol% or more and 1.0 mol% or less).

[0122] The number of aluminum atoms contained in the second additive element source (A2 source) is preferably 0.05% or more and 4.0% or less, more preferably 0.20% or more and 2.0% or less, and still more preferably 0.20% or more and 1.0% or less, relative to the number of cobalt atoms in lithium cobaltate. For example, when using aluminum hydroxide as the aluminum source, when the number of moles of lithium cobaltate in step S10 is 100, the number of moles of aluminum hydroxide contained in the second additive element source is preferably 0.05 or more and 4.0 or less (0.05 mol% or more and 4.0 mol% or less), more preferably 0.20 or more and 2.0 or less (0.20 mol% or more and 2.0 mol% or less), and still more preferably 0.20 or more and 1.0 or less (0.20 mol% or more and 1.0 mol% or less).

[0123] Regarding steps S41 to S43 shown in FIG. 3(B), they can be performed under the same conditions as steps S21 to S23 shown in FIG. 1(D). As a result, the additive element source (A2 source) can be obtained in step S43.

[0124] Also, FIG. 3(C) shows a modified example of the steps described with reference to FIG. 3(B). In step S41 shown in FIG. 3(C), a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, each is pulverized. That is, in step S43 shown in FIG. 3(C), a plurality of second additive element sources (A2 sources) are prepared.

[0125] <Steps S51 to S53> Next, steps S51 to S53 shown in FIG. 2 can be performed under the same conditions as steps S31 to S34 shown in FIG. 1(A). The heating in step S53 is preferably performed at 800° C. or higher and 1000° C. or lower, more preferably at 800° C. or higher and 950° C. or lower, and even more preferably at 800° C. or higher and 900° C. or lower. Further, the heating time is preferably 1 hour or more and 60 hours or less, more preferably 2 hours or more and 20 hours or less, and even more preferably 2 hours or more and 10 hours or less. Note that the heating in step S53 preferably has a lower heating temperature and a shorter heating time than step S33. Through the above steps, in step S54, the positive electrode active material 100 of one embodiment of the present invention can be produced. The positive electrode active material of one embodiment of the present invention has a smooth surface.

[0126] As shown in FIGS. 2 to 3(C), in Production Method 2, the addition of the additive elements to lithium cobaltate is performed separately for additive element A1 and additive element A2. By adding them separately for additive element A1 and additive element A2, the distribution of each additive element in the depth direction can be changed. For example, it is also possible to distribute additive element A1 so that it has a higher concentration in the surface layer part of the positive electrode active material than in the interior, and to distribute additive element A2 so that it has a higher concentration in the interior than in the surface layer part.

[0127] The content of this embodiment can be freely combined with the content of other embodiments.

[0128] (Embodiment 2) In this embodiment, a battery and a positive electrode active material of one embodiment of the present invention will be described.

[0129] [Battery] A lithium ion battery of one embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte. When the electrolyte contains an electrolytic solution, it has a separator between the positive electrode and the negative electrode. Further, it may have an exterior body that covers at least a part of the surroundings of the positive electrode, the negative electrode, and the electrolyte.

[0130] In this embodiment, the positive electrode and the positive electrode active material of a battery according to one aspect of the present invention will be mainly described. The positive electrode active material is the positive electrode active material 100 whose manufacturing method was described as an example in Embodiment 1. Further, details of the remaining configuration of the lithium-ion battery according to one aspect of the present invention will be described in Embodiment 3.

[0131] FIG. 4(A) is a schematic cross-sectional view for explaining the internal structure of the lithium-ion battery 10. The lithium-ion battery 10 includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22 on the positive electrode current collector 21, and the negative electrode 12 has a negative electrode current collector 31 and a negative electrode active material layer 32. As shown in the figure, the positive electrode active material layer 22 and the negative electrode active material layer 32 face each other with the separator 13 interposed therebetween. Although not shown in FIG. 4(A), the voids in the positive electrode active material layer 22, the voids in the separator 13, and the voids in the negative electrode active material layer 32 contain an electrolyte.

[0132] In FIG. 4(A), one positive electrode 11, one negative electrode 12, and one separator 13 are shown, but the lithium-ion battery according to one aspect of the present invention is not limited to this structure. A structure having two positive electrodes 11, two negative electrodes 12, and two separators 13 may be used, or more layers may be stacked. Also, instead of the stacked structure shown in FIG. 4(A), a wound structure may be used.

[0133] FIG. 4(B) is an enlarged view of the portion A surrounded by a broken line in FIG. 4(A).

[0134] The positive electrode active material layer 22 includes a positive electrode active material 100 (also referred to as a first positive electrode active material), a second positive electrode active material 200, and a conductive material 41. Although not shown, in addition to the positive electrode active material 100, the second positive electrode active material 200, and the conductive material 41, a binder may be included.

[0135] Also, the voids in the positive electrode active material layer 22 are preferably filled with the electrolyte 51 as shown in the figure. For example, it is preferable that 60% or more of the voids in the positive electrode active material layer 22 are filled with the electrolyte 51, more preferably 70% or more, still more preferably 80% or more, still more preferably 90% or more, still more preferably 95% or more, and most preferably 99% or more. The voids in the positive electrode active material layer 22 refer to the regions other than the solid components (positive electrode active material, conductive material, etc.) in the positive electrode active material layer 22.

[0136] [Positive Electrode] The positive electrode 11 includes a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 contains a positive electrode active material 100, and the positive electrode active material 100 is a particle group composed of a plurality of particles.

[0137] <Positive Electrode Active Material 100> The positive electrode active material 100 has a function of taking in lithium ions and a function of releasing them during charge and discharge. As a positive electrode active material used in one aspect of the present invention, a material with less deterioration during charge and discharge (hereinafter also referred to as "charge and discharge") can be used even at a high charging voltage (hereinafter also referred to as "high charging voltage"). Specifically, a positive electrode active material (composite oxide) obtained by the method for producing a positive electrode active material described in Embodiment 1, having a particle diameter (median diameter (D50)) of 10 μm or more and 50 μm or less, preferably 9 μm or more and 25 μm or less, can be used. The positive electrode active material 100 contains any one or more of an additive element X, an additive element Y, and an additive element Z. Details of the additive element X, the additive element Y, and the additive element Z will be described in <Contained Elements>. Incidentally, the additive element X, the additive element Y, and the additive element Z may be collectively referred to as an additive element A.

[0138] Note that the positive electrode active material 100 is the main constituent material of the positive electrode active material layer 22. Among the weight of the solid components of the positive electrode active material layer 22, the weight of the positive electrode active material 100 is preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. If the particle size of the positive electrode active material 100 is too small, the surface area will become too large, and there is a risk that the reaction between the positive electrode active material surface and the electrolyte will become excessive. For this reason, the particle size (median diameter (D50)) of the positive electrode active material is preferably 10 μm or more. Also, when the particle size of the positive electrode active material is larger than the thickness of the active material layer described later, the particle density of the active material layer cannot be increased. Therefore, the particle size of the largest particle is preferably 50 μm or less.

[0139] The particle size can be measured by a particle size distribution meter (laser diffraction type particle size distribution measuring device) using the laser diffraction / scattering method or the like. D50 is the particle size when the integrated amount occupies 50% in the cumulative curve of the particle size distribution measurement result. The measurement of the particle size is not limited to the laser diffraction type particle size distribution measurement, and the major axis of the particle cross section may be measured by analysis such as SEM (Scanning Electron Microscope) or TEM. Note that, as a method for measuring D50 from analysis such as SEM or TEM, for example, 20 or more particles can be measured, a cumulative curve can be created, and the particle size when the integrated amount occupies 50% can be defined as D50.

[0140] Note that unless otherwise specified in this specification or the like, the "charging voltage" is expressed based on the potential of lithium metal. Also, in this specification or the like, the "high charging voltage" is, for example, a charging voltage of 4.5 V or more, preferably 4.55 V or more, more preferably 4.6 V or more, 4.65 V or more, or 4.7 V or more.

[0141] Also, as described above, in this specification and the like, the "high charging voltage" is set to 4.6 V or more based on the potential when the negative electrode is lithium metal. However, when the potential is based on the case where the negative electrode is a carbon material (for example, graphite), 4.5 V or more shall be referred to as the "high charging voltage". Simply put, in the case of a half-cell using lithium metal as the negative electrode, a charging voltage of 4.6 V or more is referred to as the high charging voltage, and in the case of a full cell using a carbon material (for example, graphite) as the negative electrode, a charging voltage of 4.5 V or more is referred to as the high charging voltage.

[0142] The positive electrode active material 100 with less deterioration accompanying repeated charging and discharging at a high charging voltage will be described with reference to FIGS. 5(A) to 6(F).

[0143] FIGS. 5(A) and 5(B) are cross-sectional views of the positive electrode active material 100 which is one aspect of the present invention. FIGS. 6(A) to 6(C) show an enlarged view of the vicinity of A - B in FIG. 5(B). Also, FIGS. 6(D) to 6(F) show an enlarged view of the vicinity of C - D in FIG. 5(B).

[0144] As shown in FIG. 5(A), the positive electrode active material 100 has a surface layer portion 100a and an interior 100b. The boundary between the surface layer portion 100a and the interior 100b is shown by a broken line in these figures.

[0145] The surface layer portion 100a of the positive electrode active material 100 refers to, for example, a region within 50 nm from the surface toward the interior, more preferably within 35 nm from the surface toward the interior, still more preferably within 20 nm from the surface toward the interior, and most preferably within 10 nm from the surface toward the interior in a direction perpendicular or substantially perpendicular to the surface. Note that substantially perpendicular means 80° or more and 100° or less. A surface generated by a crack and / or a crack may also be referred to as the surface. The surface layer portion 100a is synonymous with the vicinity of the surface, the region near the surface, or the shell.

[0146] Also, a region deeper than the surface layer portion 100a of the positive electrode active material is referred to as the interior 100b. The interior 100b is synonymous with the interior region or the core.

[0147] Also, when the positive electrode active material 100 has a layered rock salt-type crystal structure of space group R-3m, as shown in FIG. 5(B), the surface layer portion 100a has an edge region 100a1 and a basal region 100a2. In FIGS. 5(A) and 5(B), the straight line marked with (00l) represents the (00l) plane. Here, the edge region 100a1 has a surface exposed in a direction intersecting the (00l) plane, and within 50 nm from the surface toward the inside, more preferably within 35 nm from the surface toward the inside, still more preferably within 20 nm from the surface toward the inside, and most preferably within 10 nm perpendicular or substantially perpendicular to the surface from the surface toward the inside is defined as the edge region 100a1. Here, the term "intersecting" means that the angle formed by the perpendicular to the first plane ((00l) plane) and the normal to the second plane (the surface of the positive electrode active material 100) is 10 degrees or more and 90 degrees or less, more preferably 30 degrees or more and 90 degrees or less.

[0148] Further, the basal region 100a2 has a surface parallel to the (00l) plane, and within 50 nm from the surface toward the inside, more preferably within 35 nm from the surface toward the inside, still more preferably within 20 nm from the surface toward the inside, and most preferably within 10 nm perpendicular or substantially perpendicular to the surface from the surface toward the inside is defined as the basal region 100a2. Here, the term "parallel" means that the angle formed by the perpendicular to the first plane ((00l) plane) and the normal to the second plane (the surface of the positive electrode active material 100) is 0 degrees or more and 5 degrees or less, more preferably 0 degrees or more and 2.5 degrees or less.

[0149] The surface of the positive electrode active material 100 shall refer to the surface of the composite oxide including the above surface layer portion 100a and the inside 100b. Therefore, the positive electrode active material 100 does not contain metal oxides adhering to the surface such as aluminum oxide (Al2O3) that does not have lithium sites capable of contributing to charge and discharge, carbonates chemisorbed after the production of the positive electrode active material, hydroxy groups, etc. The adhering metal oxide refers to, for example, a metal oxide whose crystal orientation does not match that of the inside 100b.

[0150] The approximate alignment of the crystal orientations of the two regions can be determined from TEM images, STEM images, HAADF-STEM images, ABF-STEM images, electron diffraction patterns, etc. It can also be determined from the FFT patterns of TEM images and the FFT patterns of STEM images, etc. Furthermore, XRD, neutron diffraction, etc. can also be used as materials for determination.

[0151] It is also assumed not to contain an electrolyte, a decomposition product of the electrolyte, an organic solvent, a binder, a conductive material, or a compound derived therefrom, attached to the positive electrode active material 100.

[0152] Since the positive electrode active material 100 is a compound having a transition metal capable of inserting and extracting lithium and oxygen, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) and oxygen that undergo redox reactions with the insertion and extraction of lithium exist and the region where they do not exist is defined as the surface of the positive electrode active material. A surface generated by slip, crack, and / or fracture may also be referred to as the surface of the positive electrode active material. When subjecting the positive electrode active material to analysis, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. As the protective film, a single-layer film or a multilayer film such as carbon, metal, oxide, resin, etc. may be used.

[0153] <Elements contained> The positive electrode active material 100 contains lithium, cobalt, oxygen, and an additive element. Alternatively, the positive electrode active material 100 can have an additive element added to lithium cobaltate (LiCoO2). However, the positive electrode active material 100 of one aspect of the present invention preferably has a crystal structure described later. Therefore, the composition of lithium cobaltate is not strictly limited to Li:Co:O = 1:1:2.

[0154] The cathode active material of a lithium-ion secondary battery needs to have a transition metal capable of redox in order to maintain charge neutrality even when lithium ions are inserted and extracted. It is preferable to mainly use cobalt as the transition metal responsible for the redox reaction in the cathode active material 100 according to one aspect of the present invention. In addition to cobalt, at least one or two or more selected from nickel and manganese may be used. Among the transition metals included in the cathode active material 100, when cobalt is 75 atomic% or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, there are many advantages such as relatively easy synthesis, easy handling, and excellent cycle characteristics, which is preferable.

[0155] Also, when cobalt among the transition metals of the cathode active material 100 is 75 atomic% or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, compared with a composite oxide in which nickel such as lithium nickelate (LiNiO2) occupies more than half of the transition metals, Li x The stability when x in CoO2 is small is more excellent. This is presumably because cobalt is less affected by the distortion due to the Jahn-Teller effect than nickel. The Jahn-Teller effect in a transition metal compound varies in the strength of the effect depending on the number of electrons in the d orbitals of the transition metal. In a layered rock salt-type composite oxide in which octahedrally coordinated low-spin nickel (III) such as lithium nickelate occupies more than half of the transition metals, the influence of the Jahn-Teller effect is large, and distortion is likely to occur in the layer composed of octahedrons of nickel and oxygen. Therefore, there is an increased concern about the collapse of the crystal structure during the charge-discharge cycle. Also, nickel ions are larger than cobalt ions and are close to the size of lithium ions. Therefore, there is a problem that cation mixing of nickel and lithium easily occurs in a layered rock salt-type composite oxide in which nickel occupies more than half of the transition metals such as lithium nickelate.

[0156] As the additive element(s) that the positive electrode active material 100 has, it is preferable to use one or more selected from magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, and beryllium. Further, the sum of transition metals among the additive elements is preferably less than 25 atomic %, more preferably less than 10 atomic %, and even more preferably less than 5 atomic %.

[0157] That is, the positive electrode active material 100 can be any one or more of lithium cobaltate having magnesium, lithium cobaltate having magnesium and aluminum, lithium cobaltate having magnesium and nickel, lithium cobaltate having magnesium, aluminum, and nickel, lithium cobaltate having magnesium and fluorine, lithium cobaltate having magnesium, fluorine, and nickel, lithium cobaltate having magnesium, fluorine, nickel, and aluminum, etc.

[0158] Also, as the positive electrode active material 100, a positive electrode active material having cobalt, oxygen, and magnesium, a positive electrode active material having cobalt, oxygen, magnesium, and aluminum, a positive electrode active material having cobalt, oxygen, magnesium, and nickel, a positive electrode active material having cobalt, oxygen, magnesium, aluminum, and nickel, a positive electrode active material having cobalt, oxygen, magnesium, and fluorine, a positive electrode active material having cobalt, oxygen, magnesium, fluorine, and aluminum, a positive electrode active material having cobalt, oxygen, magnesium, fluorine, and nickel, and a positive electrode active material having cobalt, oxygen, magnesium, fluorine, nickel, and aluminum, etc., any one or more of them can be used in a lithium ion battery.

[0159] The added elements are preferably dissolved in the positive electrode active material 100. For example, when performing line analysis by STEM-EDX, the position where the added elements start to be detected in the depth direction is preferably deeper than the position where the transition metal M starts to be detected, that is, located on the inner side of the positive electrode active material 100. In the line analysis by STEM-EDX in the depth direction, the position where a certain element starts to be detected refers to the position where the detection amount of the characteristic X-ray caused by the element starts to increase continuously.

[0160] These added elements stabilize the crystal structure of the positive electrode active material 100 as described later.

[0161] Note that the added elements do not necessarily have to contain magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, or beryllium.

[0162] For example, when the positive electrode active material 100 substantially does not contain titanium, the above advantages such as having excellent cycle characteristics become more significant. The weight of titanium contained in the positive electrode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less. Also, when performing STEM-EDX analysis on the positive electrode active material 100, it is preferable that the characteristic X-ray caused by titanium is not confirmed, that is, it is less than the detection lower limit (for example, less than 0.3 atomic%).

[0163] For example, when the positive electrode active material 100 substantially does not contain manganese, the above advantages such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics become more significant. The weight of manganese contained in the positive electrode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0164] The surface part 100a is the region where lithium ions first desorb during charging, and is a region where the lithium concentration is likely to be lower than that of the interior 100b. Also, the atoms on the surface of the particles of the positive electrode active material 100 in the surface part 100a can be said to be in a state where some of the bonds are broken. Therefore, the surface part 100a is likely to become unstable and can be said to be a region where the deterioration of the crystal structure easily begins. On the other hand, if the surface part 100a can be made sufficiently stable, Li x Even when x in LiCoO2 is small, for example, when x is 0.24 or less, it is possible to make it difficult to break the layered structure composed of octahedrons of cobalt and oxygen in the interior 100b. Furthermore, it is possible to suppress the displacement of the layer composed of octahedrons of cobalt and oxygen in the interior 100b.

[0165] In order to make the surface part 100a have a stable composition and crystal structure, it is preferable that the surface part 100a has additive elements, and it is more preferable that it has a plurality of additive elements. Also, it is preferable that the surface part 100a has a higher concentration of one or more selected from the additive elements than the interior 100b. Also, it is preferable that one or more selected from the additive elements possessed by the positive electrode active material 100 have a concentration gradient. Also, it is more preferable that the distribution of the positive electrode active material 100 is different depending on the additive element. For example, it is more preferable that the depth from the surface of the concentration peak is different depending on the additive element. Here, the concentration peak refers to the maximum value of the concentration in the surface part 100a or within 50 nm from the surface.

[0166] [Distribution] The distribution of the additive elements will be described. FIGS. 6(A) to 6(C) are enlarged views of the vicinity of A-B in FIG. 5(B) and are diagrams for explaining the edge region 100a1 of the positive electrode active material 100. Also, FIGS. 6(D) to 6(F) are enlarged views of the vicinity of C-D in FIG. 5(B) and are diagrams for explaining the basal region 100a2 of the positive electrode active material 100.

[0167] For example, some of the additive elements, such as magnesium, fluorine, silicon, phosphorus, boron, calcium, etc., preferably have a concentration gradient that increases from the interior 100b towards the surface, as shown by the gradation in FIGS. 6(A) and 6(D). The additive element having such a concentration gradient will be referred to as additive element X.

[0168] Another additive element, such as aluminum, manganese, etc., preferably has a concentration gradient and has a concentration peak in a region deeper than the additive element X shown in FIGS. 6(A) and 6(D), as shown by the density of the hatching in FIGS. 6(B) and 6(E). The concentration peak may be present in the surface layer portion 100a or may be deeper than the surface layer portion 100a. For example, it preferably has a peak in a region of 5 nm or more and 30 nm or less from the surface towards the interior. The additive element having such a concentration gradient will be referred to as additive element Y.

[0169] Another additive element, such as nickel, barium, etc., clearly exists in the edge region 100a1, but may not substantially exist in the basal region 100a2, as shown by the presence or absence and the density of the hatching in FIGS. 6(C) and 6(F). Here, "clearly exists" means that the characteristic X-ray energy spectrum of the element is detected in the cross-sectional STEM-EDX analysis of the positive electrode active material 100. Also, "substantially does not exist" means that the characteristic X-ray energy spectrum of the element is not detected in the cross-sectional STEM-EDX analysis of the positive electrode active material 100. This is also referred to as the case where the element is below the detection limit in the STEM-EDX analysis. In this case, in the STEM-EDX analysis, it is also said that the element is below the detection limit. The additive element having such a distribution will be referred to as additive element Z.

[0170] For example, magnesium, which is one of the additive elements X, has a valence of 2, and magnesium ions are more stable in lithium sites than in cobalt sites in a layered rock salt crystal structure. Therefore, magnesium ions tend to enter lithium sites. When magnesium is present in the lithium sites of the surface layer portion 100a at an appropriate concentration, it becomes easier to maintain the layered rock salt crystal structure. This is presumably because magnesium present in the lithium sites functions as a pillar supporting the CoO2 layers. Also, due to the presence of magnesium, x the desorption of oxygen around magnesium can be suppressed when x in LiCoO2 is, for example, 0.24 or less. Also, it can be expected that the density of the positive electrode active material 100 will increase due to the presence of magnesium. Further, when the magnesium concentration in the surface layer portion 100a is high, it can also be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution will be improved.

[0171] Magnesium can enjoy the above-mentioned advantages without adversely affecting the insertion and desorption of lithium during charge and discharge as long as it is at an appropriate concentration. However, if there is an excess of magnesium, it may have an adverse effect on the insertion and desorption of lithium. Furthermore, the effect on the stabilization of the crystal structure may be reduced. This is thought to be because magnesium starts to enter cobalt sites in addition to lithium sites. In addition, there is a possibility that excess magnesium compounds (oxides, fluorides, etc.) that do not substitute for either lithium sites or cobalt sites segregate on the surface of the positive electrode active material and become a resistance component of the secondary battery. Also, the discharge capacity of the positive electrode active material may decrease as the magnesium concentration of the positive electrode active material increases. This is thought to be because too much magnesium enters the lithium sites, reducing the amount of lithium contributing to charge and discharge.

[0172] Therefore, it is preferable that the amount of magnesium in the entire positive electrode active material 100 is appropriate. For example, the number of magnesium atoms is preferably 0.001 times or more and 0.1 times or less the number of cobalt atoms, more preferably more than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times. The amount of magnesium in the entire positive electrode active material 100 referred to here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the process of manufacturing the positive electrode active material 100.

[0173] In addition, aluminum, which is one of the additive elements Y, may be present at the cobalt site in the layered rock salt type crystal structure. Since aluminum is a trivalent typical element and its valence does not change, lithium around aluminum is less likely to move even during charge and discharge. Therefore, aluminum and lithium around it can function as pillars and suppress changes in the crystal structure. In addition, aluminum suppresses the elution of surrounding cobalt and has the effect of improving the continuous charge resistance. Also, since the Al-O bond is stronger than the Co-O bond, the desorption of oxygen around aluminum can be suppressed. Due to these effects, the thermal stability is improved. Therefore, when aluminum is included as an additive element, the safety when the positive electrode active material 100 is used in a secondary battery can be improved. Also, the positive electrode active material 100 can be made such that the crystal structure is not easily broken even when charge and discharge are repeated.

[0174] On the other hand, if aluminum is excessive, it may have an adverse effect on the insertion and desorption of lithium.

[0175] Therefore, it is preferable that the amount of aluminum in the entire positive electrode active material 100 is appropriate. For example, the number of aluminum atoms in the entire positive electrode active material 100 is preferably 0.05% or more and 4% or less, more preferably 0.1% or more and 2% or less, still more preferably 0.3% or more and 1.5% or less, based on the number of cobalt atoms. Or preferably 0.05% or more and 2% or less. Or preferably 0.1% or more and 4% or less. Here, the amount in the entire positive electrode active material 100 may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the process of producing the positive electrode active material 100.

[0176] Moreover, nickel, which is one of the additive elements Z, can exist in either the cobalt site or the lithium site. When it exists in the cobalt site, since the redox potential becomes lower compared to cobalt, it leads to an increase in discharge capacity, which is preferable.

[0177] Moreover, when nickel exists in the lithium site, the deviation of the layered structure composed of octahedrons of cobalt and oxygen can be suppressed. Also, the volume change accompanying charge and discharge is suppressed. Further, the elastic modulus increases, that is, it becomes harder. This is presumably because nickel existing in the lithium site also functions as a pillar supporting the CoO2 layers. Therefore, it can be expected that the crystal structure becomes more stable particularly in the charged state at a high temperature, for example, 45 °C or higher, which is preferable.

[0178] On the other hand, if nickel is excessive, the influence of the strain due to the Jahn-Teller effect is strengthened, which is not preferable. Also, if nickel is excessive, there is a possibility of having an adverse effect on the insertion and desorption of lithium.

[0179] Therefore, it is preferable that the nickel content in the entire positive electrode active material 100 is appropriate. For example, the atomic number of nickel in the positive electrode active material 100 is preferably more than 0% and not more than 7.5% of the atomic number of cobalt, more preferably not less than 0.05% and not more than 4%, still more preferably not less than 0.1% and not more than 2%, and even more preferably not less than 0.2% and not more than 1%. Or preferably more than 0% and not more than 4%. Or preferably more than 0% and not more than 2%. Or preferably not less than 0.05% and not more than 7.5%. Or preferably not less than 0.05% and not more than 2%. Or preferably not less than 0.1% and not more than 7.5%. Or preferably not less than 0.1% and not more than 4%. The nickel content shown here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the process of manufacturing the positive electrode active material.

[0180] In addition, fluorine, which is one of the additive elements X, is a monovalent anion. When a part of oxygen is replaced by fluorine in the surface layer portion 100a, the lithium desorption energy becomes smaller. This is because the valence change of cobalt ions accompanying lithium desorption is from trivalent to tetravalent when there is no fluorine, and from divalent to trivalent when there is fluorine, and the redox potential is different. Therefore, when a part of oxygen is replaced by fluorine in the surface layer portion 100a of the positive electrode active material 100, it can be said that the desorption and insertion of lithium ions near fluorine occur smoothly. Therefore, when the positive electrode active material 100 is used in a secondary battery, charge-discharge characteristics, high-current characteristics, etc. can be improved. In addition, the presence of fluorine in the surface layer portion 100a having a surface that is in contact with the electrolytic solution can effectively improve the corrosion resistance against hydrofluoric acid. Also, as described in Embodiment 1, when the melting point of fluoride such as lithium fluoride is lower than the melting point of other additive element sources, it can function as a flux (also referred to as a fluxing agent) that lowers the melting point of other additive element sources.

[0181] Also, as shown in FIGS. 6(A) and 6(C), when the surface layer portion 100a has both magnesium and nickel, divalent nickel may exist more stably near divalent magnesium. Therefore, Li xEven when x in CoO2 is small, elution of magnesium can be suppressed. Therefore, it can contribute to the stabilization of the surface layer portion 100a.

[0182] Also, when having different distributed additive elements such as additive element X, additive element Y, and additive element Z together, it is preferable because the crystal structure in a wider region can be stabilized. For example, when the positive electrode active material 100 has both magnesium which is one of the additive elements X, aluminum which is one of the additive elements Y, and nickel which is one of the additive elements Z, the crystal structure in a wider region can be stabilized compared to the case of having only one or two of the additive elements X, additive element Y, and additive element Z. When the positive electrode active material 100 has the additive elements X, additive element Y, and additive element Z together in this way, the surface stabilization can be sufficiently achieved by the additive elements X such as magnesium and the additive elements Z such as nickel, so the additive element Y such as aluminum is not essential on the surface. Rather, it is preferable that aluminum is widely distributed in a deeper region. For example, it is preferable that aluminum is continuously detected in the region from the surface in the depth direction of 1 nm or more and 25 nm or less. When aluminum is widely distributed in this way, the crystal structure in a wider region can be stabilized, which is preferable.

[0183] Also, when the additive element Z is contained in a large amount (also referred to as preferentially contained, selectively contained, etc.) in the edge region 100a1 as shown in FIGS. 6(C) and 6(F), it is preferable because the stability of the crystal structure of the edge region 100a1 where lithium ions enter and exit the positive electrode active material 100 during charging and discharging of the lithium ion battery is improved. Further, when the additive element Z has the above-described distribution, for example, when the positive electrode active material 100 is lithium cobaltate, the influence such as a decrease in discharge voltage or a decrease in discharge capacity due to adding the additive element Z can be minimized, so it is preferable.

[0184] When having a plurality of additive elements as described above, the effects of the respective additive elements can synergistically contribute to further stabilization of the surface layer portion 100a. In particular, having magnesium, nickel, and aluminum is highly preferable because it has a high effect of achieving a stable composition and crystal structure. Among these, in the surface layer portion 100a of the positive electrode active material 100, it is preferable to have a region where magnesium is distributed closer to the surface side than aluminum. Further, in addition to the regions where magnesium and aluminum are distributed as described above, it is most preferable to have a region where the distribution of nickel overlaps with the distribution of magnesium in the edge region 100a1 of the surface layer portion 100a of the positive electrode active material 100.

[0185] <Crystal structure> <Li x When x in CoO2 is 1> The positive electrode active material 100 according to one aspect of the present invention is in a discharged state, that is, Li x When x = 1 in CoO2, it preferably has a layered rock salt-type crystal structure belonging to the space group R-3m. The layered rock salt-type composite oxide has a high discharge capacity, has a two-dimensional lithium ion diffusion path, and is suitable for the insertion / desorption reaction of lithium ions, and is excellent as a positive electrode active material for a secondary battery. Therefore, in particular, it is preferable that the interior 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock salt-type crystal structure.

[0186] On the other hand, the surface layer portion 100a of the positive electrode active material 100 according to one aspect of the present invention preferably has a function of reinforcing so that the layered structure composed of the transition metal M and oxygen octahedra in the interior 100b does not break even when lithium is removed from the positive electrode active material 100 by charging. Or it is preferable that the surface layer portion 100a functions as a barrier film for the positive electrode active material 100. Or it is preferable that the surface layer portion 100a, which is the outer peripheral portion of the positive electrode active material 100, reinforces the positive electrode active material 100. The reinforcement here means suppressing the structural changes in the surface layer portion 100a and the interior 100b of the positive electrode active material 100 including oxygen desorption, and / or suppressing the oxidative decomposition of the electrolyte on the surface of the positive electrode active material 100.

[0187] Therefore, it is preferable that the surface layer portion 100a has a crystal structure different from that of the interior 100b. Further, it is preferable that the surface layer portion 100a has a composition and a crystal structure that are more stable at room temperature (25°C) than the interior 100b. For example, at least a part of the surface layer portion 100a of the positive electrode active material 100 according to one aspect of the present invention preferably has a rock salt-type crystal structure. Alternatively, it is preferable that the surface layer portion 100a has both a layered rock salt-type and a rock salt-type crystal structure. Alternatively, it is preferable that the surface layer portion 100a has characteristics of both a layered rock salt-type and a rock salt-type crystal structure.

[0188] Although it is preferable that a part of the additive element A, particularly magnesium, nickel, and aluminum, has a higher concentration in the surface layer portion 100a than in the interior 100b, it is preferable that they are also randomly and thinly present in the interior 100b. When magnesium and aluminum are present in the lithium sites of the interior 100b at appropriate concentrations, there is an effect such that it is possible to easily maintain a layered rock salt-type crystal structure as described above. When nickel is present in the interior 100b at an appropriate concentration, a deviation of the layered structure composed of octahedra of transition metal M and oxygen can be suppressed as described above. When magnesium and nickel are combined, there is a possibility that divalent magnesium can exist more stably near divalent nickel, so a synergistic effect of suppressing the elution of magnesium can be expected.

[0189] Due to the concentration gradient of the additive element A as described above, it is preferable that the crystal structure continuously changes from the interior 100b toward the surface. Alternatively, it is preferable that the crystal orientations of the surface layer portion 100a and the interior 100b are substantially the same.

[0190] For example, it is preferable that the crystal structure continuously changes from the layered rock salt-type interior 100b toward the surface and the surface layer portion 100a having characteristics of both a rock salt-type and a layered rock salt-type. Alternatively, it is preferable that the crystal orientations of the surface layer portion 100a having characteristics of both a rock salt-type and a layered rock salt-type and the layered rock salt-type interior 100b are substantially the same.

[0191] In the present specification and the like, the layered rock-salt type crystal structure belonging to the space group R-3m, which a composite oxide containing a transition metal M including lithium and cobalt has, means a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and since the transition metal M and lithium are regularly arranged to form a two-dimensional plane, it is a crystal structure in which two-dimensional diffusion of lithium is possible. Note that there may be defects such as deficiencies of cations or anions. Also, strictly speaking, the layered rock-salt type crystal structure may be a structure in which the lattice of the rock-salt type crystal is distorted.

[0192] Also, the rock-salt type crystal structure means a crystal structure of the cubic crystal system including a crystal structure belonging to the space group Fm-3m, and has a structure in which cations and anions are alternately arranged. Note that there may be deficiencies of cations or anions.

[0193] Also, having both the characteristics of the layered rock-salt type and the rock-salt type crystal structures can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0194] There is no distinction in the cation sites in the rock-salt type, but in the layered rock-salt type, there are two types of cation sites in the crystal structure. One is mostly occupied by lithium, and the other is occupied by the transition metal M. The stacked structure in which the two-dimensional plane of cations and the two-dimensional plane of anions are alternately arranged is the same for both the rock-salt type and the layered rock-salt type. Among the bright spots of the electron diffraction pattern corresponding to the crystal plane forming this two-dimensional plane, when the central spot (transmission spot) is taken as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in the ideal rock-salt type and the (003) plane in the layered rock-salt type. For example, when comparing the electron diffraction patterns of rock-salt type MgO and layered rock-salt type LiCoO2, the bright spot of the (003) plane of LiCoO2 is observed at a position approximately half the distance between the bright spots of the (111) plane of MgO. Therefore, when the analysis region has, for example, two phases of rock-salt type MgO and layered rock-salt type LiCoO2, in the electron diffraction pattern, there exists a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are alternately arranged. The bright spots common to the rock-salt type and the layered rock-salt type have strong brightness, and the bright spots that occur only in the layered rock-salt type have weak brightness.

[0195] In the cross-sectional STEM image or the like, when observing the layered rock salt-type crystal structure from a direction perpendicular to the c-axis, layers observed with strong brightness and layers observed with weak brightness are alternately observed. Since there is no distinction in the cation sites in the rock salt-type, such a feature is not observed. In the case of a crystal structure having the characteristics of both the rock salt-type and the layered rock salt-type, when observed from a specific crystal orientation, in the cross-sectional STEM image or the like, layers observed with strong brightness and layers observed with weak brightness are alternately observed, and furthermore, in a part of the layer with weaker brightness, that is, the lithium layer, a metal having an atomic number larger than that of lithium exists.

[0196] 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). It is presumed that the anions of the O3'-type crystal described later also adopt a cubic close-packed structure. Therefore, when the layered rock salt-type crystal and the rock salt-type crystal are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned.

[0197] Or, it can also be explained as follows. The anions on the {111} plane of the cubic crystal structure have a triangular lattice. The layered rock salt-type has a space group of R-3m and is a rhombohedral structure, but is generally represented by a composite hexagonal lattice for easy understanding of the structure, and the (0001) plane of the layered rock salt-type has a hexagonal lattice. The triangular lattice of the cubic crystal {111} plane has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock salt-type. The fact that the lattices of the two are consistent can be said that the orientations of the cubic close-packed structures are aligned.

[0198] However, since the space groups of the layered rock salt-type crystal and the O3'-type crystal are R-3m, which is different from the space group Fm-3m of the rock salt-type crystal (the space group of a general rock salt-type crystal), the Miller indices of the crystal planes satisfying the above conditions are different between the layered rock salt-type crystal and the O3'-type crystal and the rock salt-type crystal. In this specification, in the case of the layered rock salt-type crystal, the O3'-type, and the rock salt-type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are generally in agreement.

[0199] <Li xCoO2 with small x> The positive electrode active material 100 according to one embodiment of the present invention has the above-described distribution of the additive element A and / or crystal structure in a discharged state, and therefore has a high degree of conductivity. x The crystal structure when x in CoO2 is small is different from that of conventional positive electrode active materials. <x≦0.24をいうこととする。

[0200] Using Figs. 7 to 10, Li x The change in crystal structure accompanying the change in x in CoO2 will be described while comparing a conventional positive electrode active material with a positive electrode active material 100 according to one embodiment of the present invention.

[0201] The change in the crystal structure of a conventional positive electrode active material is shown in Figure 8. The conventional positive electrode active material shown in Figure 8 is lithium cobalt oxide (LiCoO2) that does not contain the added element A in particular.

[0202] Figure 8 shows R-3m O3 and Li x The crystal structure of lithium cobalt oxide with x=1 in CoO2 is shown. In this crystal structure, lithium occupies the octahedral site, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3 type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and the edges are shared to form a continuous plane. This is sometimes called a layer made of octahedra of cobalt and oxygen.

[0203] In addition, conventional lithium cobalt oxide is known to have a crystal structure that belongs to the monoclinic space group P2 / m when the symmetry of lithium increases when x is about 0.5. This structure has one CoO2 layer in the unit cell. Therefore, it is sometimes called O1 type or monoclinic O1 type.

[0204] When x = 0, the cathode active material has a crystal structure of the trigonal space group P-3m1, and there is also one layer of CoO2 in the unit cell. Therefore, this crystal structure is sometimes called the O1 type or the trigonal O1 type. In addition, the trigonal crystal may be converted into a composite hexagonal lattice and sometimes called the hexagonal O1 type.

[0205] Conventional lithium cobaltate when x is about 0.12 has a crystal structure of the space group R-3m. This structure can also be said to be a structure in which the CoO2 structure like the trigonal O1 type and the LiCoO2 structure like the R-3m O3 are alternately stacked. Therefore, this crystal structure is sometimes called the H1-3 type crystal structure. In fact, in the H1-3 type crystal structure, the number of cobalt atoms per unit cell is twice that of other structures. However, in this specification including FIG. 8, for easy comparison with other crystal structures, the c-axis of the H1-3 type crystal structure will be shown in a figure with the unit cell halved.

[0206] As an example, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150 ± 0.00016), O1(0, 0, 0.27671 ± 0.00045), O2(0, 0, 0.11535 ± 0.00045). O1 and O2 are oxygen atoms respectively. Which unit cell should be used to represent the crystal structure of the cathode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, the unit cell with a smaller GOF (goodness of fit) value can be adopted.

[0207] Li x When charging and discharging are repeated so that x in LiCoO2 becomes 0.24 or less, conventional lithium cobaltate will repeat the crystal structure change (i.e., non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0208] However, these two crystal structures have a large shift in the CoO2 layer. As shown by the dotted lines and arrows in Fig. 8, in the H1-3 type crystal structure, the CoO2 layer is greatly shifted from the R-3m O3 in the discharged state. Such dynamic structural changes can have an adverse effect on the stability of the crystal structure.

[0209] Furthermore, these two crystal structures also have a large volume difference. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the R-3m O3 type crystal structure in the discharged state exceeds 3.5%, typically more than 3.9%.

[0210] In addition, the structure in which the CoO2 layer is continuous, such as the trigonal O1 type, which the H1-3 type crystal structure has, is likely to be unstable.

[0211] Therefore, when charging and discharging are repeated such that x becomes 0.24 or less, the crystal structure of conventional lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is because when the crystal structure collapses, the sites where lithium can stably exist decrease, and it becomes difficult for lithium to be inserted and removed.

[0212] On the other hand, in the positive electrode active material 100 of one embodiment of the present invention shown in Fig. 7, Li x The change in the crystal structure in the discharged state where x is 1 in LiCoO2 and the state where x is 0.24 or less is less than that of the conventional positive electrode active material. More specifically, the shift of the CoO2 layer in the state where x is 1 and the state where x is 0.24 or less can be reduced. Also, the volume change when compared per cobalt atom can be reduced. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to have its crystal structure collapse even when charging and discharging are repeated such that x becomes 0.24 or less, and excellent cycle characteristics can be realized. Also, the positive electrode active material 100 of one embodiment of the present invention can have a more stable crystal structure than the conventional positive electrode active material in the state where x in Li x CoO2 is 0.24 or less. Therefore, the positive electrode active material 100 of one embodiment of the present invention is Li xWhen the state where x in CoO2 is 0.24 or less is maintained, short circuits are less likely to occur. In such a case, the safety of the secondary battery is further improved, which is preferable.

[0213] Li x When x in CoO2 is about 1 and about 0.2, the crystal structure of the interior 100b of the positive electrode active material 100 is shown in FIG. 7. Since the interior 100b occupies most of the volume of the positive electrode active material 100 and greatly contributes to charge and discharge, it can be said that the deviation and volume change of the CoO2 layer are the most problematic parts.

[0214] When x = 1, the positive electrode active material 100 has the same crystal structure of R-3m O3 as conventional lithium cobaltate.

[0215] However, when x of the positive electrode active material 100 is 0.24 or less, for example, about 0.2 or about 0.12, such that conventional lithium cobaltate has an H1-3 type crystal structure, it has crystals with a different structure.

[0216] When x is about 0.2, the positive electrode active material 100 according to one aspect of the present invention has a crystal structure belonging to the trigonal space group R-3m. This is because the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is called an O3' type crystal structure. The crystal structure is shown in FIG. 7 with R-3m O3'.

[0217] The O3' type crystal structure can show the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), 0.20 ≤ x ≤ 0.25. Also, the lattice constant of the unit cell is preferably 2.797 ≤ a ≤ 2.837 (×10 -1 nm), more preferably 2.807 ≤ a ≤ 2.827 (×10 -1 nm), and typically a = 2.817 (×10 -1 nm). The c-axis is preferably 13.681 ≤ c ≤ 13.881 (×10 -1 nm), more preferably 13.751 ≤ c ≤ 13.811, and typically c = 13.781 (×10 -1 nm).

[0218] In the O3'-type crystal structure, ions such as cobalt, nickel, and magnesium occupy the oxygen six-coordinate positions. Light elements such as lithium may occupy the oxygen four-coordinate positions.

[0219] As shown by the dotted line in FIG. 7, there is almost no shift in the CoO2 layer between the discharged R-3m(O3) and the O3'-type crystal structure.

[0220] Also, the volume difference per the same number of cobalt atoms between the discharged R-3m(O3) and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0221] Thus, in the positive electrode active material 100 of one aspect of the present invention, when x in Li x CoO2 is small, that is, when many lithium atoms are desorbed, the change in the crystal structure is suppressed more than that of the conventional positive electrode active material. Also, the change in volume when compared per the same number of cobalt atoms is suppressed. Therefore, the positive electrode active material 100 is less likely to have its crystal structure collapsed even when charging and discharging are repeated such that x becomes 0.24 or less. Therefore, the positive electrode active material 100 suppresses a decrease in the charge-discharge capacity in the charge-discharge cycle. Also, since more lithium can be stably utilized than in the conventional positive electrode active material, the positive electrode active material 100 has a large discharge capacity per unit weight and per unit volume. Therefore, by using the positive electrode active material 100, a secondary battery having a high discharge capacity per unit weight and per unit volume can be manufactured.

[0222] Note that the positive electrode active material 100 may have an O3'-type crystal structure when x in Li x CoO2 is 0.15 or more and 0.24 or less, and it is presumed to have an O3'-type crystal structure even when x exceeds 0.24 and is 0.27 or less. However, since the crystal structure is affected not only by x in Li x CoO2 but also by the number of charge-discharge cycles, charge-discharge current, temperature, electrolyte, etc., it is not necessarily limited to the above range of x.

[0223] Therefore, the positive electrode active material 100 is Li xWhen x in CoO₂ exceeds 0.1 and is 0.24 or less, not all of the interior 100b of the positive electrode active material 100 needs to have an O3' type crystal structure. It may contain other crystal structures or part of it may be amorphous.

[0224] Also, Li x In order to make x in CoO₂ in a small state, generally, it is necessary to charge at a high charging voltage. Therefore, Li x The state where x in CoO₂ is small can be rephrased as a state charged at a high charging voltage. For example, when charging at a voltage of 4.6 V or more with respect to the potential of lithium metal in an environment of 25 °C by CC / CV charging, an H1-3 type crystal structure appears in the conventional positive electrode active material. Therefore, a charging voltage of 4.6 V or more with respect to the potential of lithium metal can be said to be a high charging voltage.

[0225] Therefore, it can be rephrased that the positive electrode active material 100 of one aspect of the present invention is preferable because it can maintain a crystal structure having R-3m O3 symmetry even when charged at a high charging voltage, for example, a voltage of 4.6 V or more at 25 °C. Also, it can be rephrased that it is preferable because it can take an O3' type crystal structure when charged at an even higher charging voltage, for example, a voltage of 4.65 V or more and 4.7 V or less at 25 °C.

[0226] Even when the charging voltage of the positive electrode active material 100 is further increased, an H1-3 type crystal structure may be observed in some cases. Also, as described above, since the crystal structure is affected by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc., when the charging voltage is lower, for example, even when the charging voltage is 4.5 V or more and less than 4.6 V at 25 °C, the positive electrode active material 100 of one aspect of the present invention may take an O3' type crystal structure in some cases.

[0227] In a secondary battery, for example, when using graphite as the negative electrode active material, the voltage of the secondary battery decreases by the potential of graphite compared to the above. The potential of graphite is about 0.05 V to 0.2 V with respect to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, it has the same crystal structure at the voltage obtained by subtracting the potential of graphite from the above voltage.

[0228] Also, in O3' of FIG. 7, it is shown that lithium exists at all lithium sites with equal probability, but it is not limited to this. Lithium may be unevenly distributed at some lithium sites, or may have symmetry such as the monoclinic O1 (Li 0.5 CoO2) shown in FIG. 8. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0229] Also, it can be said that the O3'-type crystal structure is a crystal structure similar to the CdCl2-type crystal structure having lithium randomly between layers. This crystal structure similar to the CdCl2-type is close to the crystal structure when lithium nickelate is charged up to Li 0.06 NiO2, but it is known that pure lithium cobaltate or a layered rock salt-type positive electrode active material containing a large amount of cobalt usually does not take the CdCl2-type crystal structure.

[0230] Also, the concentration gradient of the additive element A is preferably the same gradient at a plurality of locations in the surface layer portion 100a of the positive electrode active material 100. That is, it is preferable that the reinforcement derived from the additive element A is homogeneously present in the surface layer portion 100a. Even if there is reinforcement in a part of the surface layer portion 100a, if there is a non-reinforced part, stress may concentrate in the non-reinforced part. When stress concentrates in a part of the positive electrode active material 100, defects such as cracks may occur therefrom, leading to cracking of the positive electrode active material and a decrease in discharge capacity.

[0231] However, it is not necessarily required that the additive element A has the same concentration gradient throughout the entire surface layer portion 100a of the positive electrode active material 100. An example of the distribution of the additive element X in the vicinity of C-D in FIG. 5(B) is shown in FIG. 6(D), and an example of the distribution of the additive element Y in the vicinity of C-D is shown in FIG. 6(E).

[0232] Here, it is assumed that the vicinity of C-D has a layered rock salt-type crystal structure of R-3m and the surface has a (001) orientation. The (001)-oriented surface may have a different distribution of the additive element A from other surfaces. For example, the (001)-oriented surface and its surface layer portion 100a may have the distribution of one or more concentration peaks selected from the additive element X and the additive element Y limited to a shallow portion from the surface as compared with the surfaces other than the (001) orientation. Or, the (001)-oriented surface and its surface layer portion 100a may have one or more concentrations selected from the additive element X and the additive element Y lower as compared with other orientations. Or, one or more elements selected from the additive element X and the additive element Y on the (001)-oriented surface and its surface layer portion 100a may be below the detection lower limit.

[0233] In the layered rock salt-type crystal structure of R-3m, cations are arranged parallel to the (001) plane. This can be said to be a structure in which CoO2 layers and lithium layers are alternately stacked parallel to the (001) plane. Therefore, the diffusion path of lithium ions also exists parallel to the (001) plane.

[0234] Since the CoO2 layer is relatively stable, the surface of the positive electrode active material 100 is more stable when it has a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.

[0235] On the other hand, the diffusion path of lithium ions is exposed on the surfaces other than the (001) orientation. Therefore, the surfaces other than the (001) orientation and the surface layer portion 100a are important regions for maintaining the diffusion path of lithium ions, and at the same time, they are likely to become unstable because they are the regions where lithium ions first desorb. Therefore, it is extremely important to reinforce the surfaces other than the (001) orientation and the surface layer portion 100a in order to maintain the crystal structure of the entire positive electrode active material 100.

[0236] Therefore, in the positive electrode active material 100 according to another aspect of the present invention, it is important that the distribution of the additive element A on the surface other than the (001) plane and its surface layer portion 100a1 is as shown in FIGS. 6(A) to 6(C). On the other hand, on the (001) plane and its surface layer portion 100a, the concentration of the additive element A may be low or may not be present as described above.

[0237] As described in Embodiment 1, in the production method in which high-purity LiCoO2 is produced and then the additive element A is mixed and heated later, the additive element A spreads mainly through the diffusion path of lithium ions. Therefore, it is easy to make the distribution of the additive element A on the surface other than the (001) plane and its surface layer portion 100a within a preferable range.

[0238] <Grain boundary> In addition to the above-described distribution, it is more preferable that at least a part of the additive element A included in the positive electrode active material 100 according to one aspect of the present invention is unevenly distributed at the grain boundaries and in the vicinity thereof.

[0239] In this specification and the like, uneven distribution means that the concentration of an element in a certain region is different from that in other regions. It is synonymous with segregation, precipitation, non-uniformity, bias, or the coexistence of a portion with a high concentration and a portion with a low concentration.

[0240] For example, it is preferable that the magnesium concentration at the grain boundaries and in the vicinity thereof in the positive electrode active material 100 is higher than that in other regions of the interior 100b. Also, it is preferable that the fluorine concentration at the grain boundaries and in the vicinity thereof is higher than that in other regions of the interior 100b. Also, it is preferable that the nickel concentration at the grain boundaries and in the vicinity thereof is higher than that in other regions of the interior 100b. Also, it is preferable that the aluminum concentration at the grain boundaries and in the vicinity thereof is higher than that in other regions of the interior 100b.

[0241] A grain boundary is one type of surface defect. Therefore, it is likely to become unstable like the surface and the change in the crystal structure is likely to start. Therefore, if the concentration of the additive element A at the grain boundaries and in the vicinity thereof is high, the change in the crystal structure can be more effectively suppressed.

[0242] Further, when the magnesium concentration and the fluorine concentration at the grain boundaries and in the vicinity thereof are high, even when cracks occur along the grain boundaries of the positive electrode active material 100 according to one embodiment of the present invention, the magnesium concentration and the fluorine concentration increase near the surface caused by the cracks. Therefore, the corrosion resistance of the positive electrode active material against hydrofluoric acid can be enhanced even after cracks occur.

[0243] <Analysis method> Whether a certain positive electrode active material is the positive electrode active material 100 according to one embodiment of the present invention having an O3'-type crystal structure when x in Li x CoO2 is small can be determined by analyzing a positive electrode having a positive electrode active material with a small x in Li x CoO2 using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc.

[0244] Particularly, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, can compare the crystallinity and crystal orientation, can analyze the periodic strain of the lattice and the crystallite size, and can obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling the secondary battery as it is. Among XRDs, powder XRD can obtain diffraction peaks reflecting the crystal structure of the interior 100b of the positive electrode active material 100 that occupies most of the volume of the positive electrode active material 100.

[0245] When analyzing the crystallite size by powder XRD, it is preferable to measure it excluding the influence of the orientation of the positive electrode active material particles due to pressure or the like. For example, it is preferable to take out the positive electrode active material from the positive electrode obtained by disassembling the secondary battery and then measure it as a powder sample.

[0246] The positive electrode active material 100 according to one embodiment of the present invention, as described above, has Li x It is characterized in that the change in the crystal structure is small when x in CoO2 is 1 and when it is 0.24 or less. When charged at a high voltage, a material in which a crystal structure with a large change in the crystal structure occupies 50% or more is not preferable because it cannot withstand repeated charging and discharging at a high voltage.

[0247] Note that simply adding additive elements may not result in an O3'-type crystal structure. For example, lithium cobaltate with magnesium and fluorine, or lithium cobaltate with magnesium and aluminum, although common in this regard, depending on the concentration and distribution of the additive elements, Li x x There are cases where in LiCoO2, when x is 0.24 or less, the O3'-type crystal structure accounts for 60% or more, and cases where the H1-3 type crystal structure occupies 50% or more.

[0248] Also, in the positive electrode active material 100 of one aspect of the present invention, when x is too small, such as 0.1 or less, or under conditions where the charging voltage exceeds 4.9 V, an H1-3 type or trigonal O1 type crystal structure may occur. Therefore, in order to determine whether it is the positive electrode active material 100 of one aspect of the present invention, analysis of the crystal structure including XRD and information such as charging capacity or charging voltage are required.

[0249] However, a positive electrode active material in a state where x is small may change its crystal structure when exposed to the atmosphere. For example, it may change from an O3'-type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples for crystal structure analysis in an inert atmosphere such as an argon atmosphere.

[0250] Also, whether the distribution of the additive elements possessed by the positive electrode active material is in the state as described above can be determined by analysis using, for example, XPS, EDX, EPMA (Electron Probe Micro Analyzer), etc.

[0251] Also, the crystal structure of the surface layer portion 100a, crystal grain boundaries, etc. can be analyzed by electron diffraction of the cross-section of the positive electrode active material 100.

[0252] <Charging method> The charging for determining whether the composite oxide is the positive electrode active material 100 of one aspect of the present invention can be carried out, for example, by fabricating a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using the composite oxide for the positive electrode and lithium metal for the counter electrode and then charging it. The coin cell has an electrolyte solution, a separator, a positive electrode can, and a negative electrode can.

[0253] More specifically, for the positive electrode, a slurry obtained by mixing a positive electrode active material, a conductive material, and a binder can be used by coating it on a positive electrode current collector made of aluminum foil.

[0254] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery is different from the potential of the positive electrode. Unless otherwise specified, the voltage and potential in this specification and the like are the potential of the positive electrode.

[0255] For the electrolyte contained in the electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiPF6) can be used. For the electrolyte solution, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of EC:DEC = 3:7 and vinylene carbonate (VC) at 2 wt% can be used.

[0256] A 25-μm-thick polypropylene porous film can be used for the separator.

[0257] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) can be used.

[0258] Charge the coin cell fabricated under the above conditions at an arbitrary voltage (e.g., 4.50 V, 4.55 V, 4.58 V, 4.60 V, 4.62 V, 4.65 V, 4.70 V, 4.75 V, or 4.80 V). The charging method is not particularly limited as long as it can be charged sufficiently at an arbitrary voltage for a sufficient time. In this specification and the like, when it is described as about 4.6 V, it refers to a voltage of 4.58 V or more and 4.62 V or less. For example, when charging by CCCV, the current in CC charging can be carried out at 20 mA / g or more and 100 mA / g or less. CV charging can be terminated at 2 mA / g or more and 10 mA / g or less. In order to observe the phase change of the positive electrode active material, it is desirable to charge at such a small current value. The temperature is 25 °C or 45 °C. After charging in this way, if the coin cell is disassembled in a glove box under an argon atmosphere to take out the positive electrode, a positive electrode active material with an arbitrary charge capacity can be obtained. When performing various analyses thereafter, in order to suppress the reaction with external components, it is preferably sealed in an argon atmosphere. For example, XRD can be carried out by enclosing it in a sealed container under an argon atmosphere. Also, after charging is completed, it is preferable to promptly take out the positive electrode for analysis. Specifically, it is preferably within 1 hour after charging is completed, and more preferably within 30 minutes.

[0259] When analyzing the crystal structure of the charged state after multiple charge and discharge cycles, for example, charging is carried out at a constant current with a current value of 20 mA / g or more and 100 mA / g or less up to an arbitrary voltage (e.g., 4.50 V, 4.55 V, 4.58 V, 4.60 V, 4.62 V, 4.65 V, 4.70 V, 4.75 V, or 4.80 V), and then charging is carried out at a constant voltage until the current value becomes 2 mA / g or more and 10 mA / g or less. Discharging can be carried out at a constant current with a voltage of 2.5 V and a current value of 20 mA / g or more and 100 mA / g or less. Or, discharging can be carried out at a constant current with a voltage of 3.0 V and a current value of 20 mA / g or more and 200 mA / g or less.

[0260] When analyzing the crystal structure of the discharged state after multiple charge and discharge cycles as well, for example, discharging can be carried out at a constant current with a voltage of 2.5 V and a current value of 20 mA / g or more and 200 mA / g or less. Or, discharging can be carried out at a constant current with a voltage of 3.0 V and a current value of 20 mA / g or more and 200 mA / g or less.

[0261] <xrd> The apparatus and conditions for XRD measurement are not particularly limited. For example, measurement can be performed under the following apparatus and conditions. XRD apparatus: D8 ADVANCE manufactured by Bruker AXS, X-ray: CuKα1, output: 40 KV, 40 mA, slit width: Div. Slit, 0.5°, detector: LynxEye, scan mode: 2θ / θ continuous scan, measurement range (2θ): 15° or more and 90° or less, step width (2θ): set to 0.01°, counting time: 1 second / step, sample stage rotation: 15 rpm.

[0262] When the measurement sample is powder, it can be set by methods such as putting it in a glass sample holder or sprinkling the sample on a silicon non-reflecting plate coated with grease. When the measurement sample is a positive electrode, the positive electrode can be attached to a substrate with double-sided tape and set with the positive electrode active material layer aligned with the measurement surface required by the apparatus.

[0263] The ideal powder XRD patterns by CuKα1 line calculated from the models of the O3’-type crystal structure and the H1-3-type crystal structure are shown in FIGS. 9 and 10. Also, for comparison, Li x The ideal XRD patterns calculated from LiCoO2O3 with x = 1 and trigonal O1 with x = 0 in LiCoO2 are also shown. The patterns of LiCoO2 (O3) and CoO2 (O1) were created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), based on the crystal structure information obtained from ICSD. The range of 2θ was set from 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562×10 -10 m, λ2 was not set, and the monochromator was set to single. The XRD pattern of the H1-3-type crystal structure was created in the same manner as above based on the information of the H1-3-type crystal structure shown in FIG. 8. The XRD pattern of the O3’-type crystal structure was estimated from the XRD pattern of the positive electrode active material of one aspect of the present invention, fitted using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as others.

[0264] As shown in Fig. 9, in the O3'-type crystal structure, diffraction peaks appear at 2θ = 19.25 ± 0.12° (19.13° or more and 19.37° or less) and 2θ = 45.47 ± 0.10° (45.37° or more and 45.57° or less).

[0265] However, as shown in Fig. 10, peaks do not appear at these positions in the H1-3 type crystal structure and trigonal O1. Therefore, Li x The appearance of diffraction peaks at 2θ = 19.25 ± 0.12° (19.13° or more and 19.37° or less) and 2θ = 45.47 ± 0.10° (45.37° or more and 45.57° or less) when x in Li

[0266] Note that as the O3'-type crystal structure, when it is slightly larger than the value of x in the XRD pattern shown in Fig. 9, for example, when charging is performed with a charging voltage upper limit of a voltage slightly lower than 4.60V (4.56V, 4.57V, 4.58V or 4.59V), the above peaks appear shifted to the low angle side. For example, when charging with 4.58V as the charging voltage upper limit, the positive electrode active material 100 has diffraction peaks at 2θ = 18.85 ± 0.20° and 2θ = 45.15 ± 0.10° as diffraction peaks derived from the O3'-type crystal structure.

[0267] This can also mean that in the crystal structures of x = 1 and x ≤ 0.24, the positions where the XRD diffraction peaks appear are close. More specifically, for the peaks that appear at 2θ of 42° or more and 46° or less among the main diffraction peaks of the crystal structures of x = 1 and x ≤ 0.24, the difference in 2θ can be 0.7° or less, more preferably 0.5° or less.

[0268] Note that the positive electrode active material 100 of one embodiment of the present invention is Li x When x in CoO2 is small, it has an O3'-type crystal structure, but not all of them need to have an O3'-type crystal structure. It may contain other crystal structures or some may be amorphous. However, when performing Rietveld analysis on the XRD pattern, it is preferably 50% or more, more preferably 60% or more, and even more preferably 66% or more of the O3'-type crystal structure. If the O3'-type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, a cathode active material with excellent cycle characteristics can be obtained.

[0269] Also, even after charging and discharging for 5 cycles or more, 30 cycles or more, 50 cycles or more, or 100 cycles or more from the start of measurement, when performing Rietveld analysis, it is preferably 35% or more, more preferably 40% or more, and even more preferably 43% or more of the O3'-type crystal structure.

[0270] Also, the sharpness of the diffraction peaks in the XRD pattern indicates the degree of crystallinity. Therefore, each diffraction peak after charging is preferably sharp, that is, has a narrow half-width. The half-width varies depending on the XRD measurement conditions or the 2θ value even for peaks arising from the same crystal phase. In the case of the above-described measurement conditions, for peaks observed at 2θ = 43° or more and 46° or less, the half-width is preferably, for example, 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not necessarily all peaks need to satisfy this requirement. If some peaks satisfy this requirement, it can be said that the crystallinity of that crystal phase is high. Such high crystallinity sufficiently contributes to the stabilization of the crystal structure after charging.

[0271] Also, the crystallite size of the O3'-type crystal structure possessed by the cathode active material 100 only decreases to about 1 / 20 of that of LiCoO2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the cathode before charge and discharge, Li x When x is small in CoO2, a distinct peak of the O3’-type crystal structure can be confirmed. On the other hand, in conventional LiCoO2, even if a part can take a structure similar to the O3’-type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0272] <xps> In the case of inorganic oxides in XPS (X-ray Photoelectron Spectroscopy), when using the Kα line of monochromatic aluminum as the X-ray, it is possible to analyze the region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less). Therefore, for a region about half the depth of the surface layer portion 100a, the concentration of each element can be quantitatively analyzed. Also, by performing narrow scan analysis, the bonding state of the elements can be analyzed. The quantitative accuracy of XPS is often about ±1 atomic %, and the detection limit is about 1 atomic % depending on the element.

[0273] In the positive electrode active material 100 according to one aspect of the present invention, it is preferable that the concentration of one or more selected from the additive elements is higher in the surface layer portion 100a than in the interior 100b. This is synonymous with the fact that it is preferable that the concentration of one or more selected from the additive elements in the surface layer portion 100a is higher than the average of the entire positive electrode active material 100. Therefore, for example, it can be said that the concentration of one or more additive elements selected from the surface layer portion 100a measured by XPS or the like is preferably higher than the average concentration of the additive elements of the entire positive electrode active material 100 measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry), GD-MS (Glow Discharge Mass Spectrometry), or the like. For example, it is preferable that the concentration of at least a part of magnesium in the surface layer portion 100a measured by XPS or the like is higher than the average magnesium concentration of the entire positive electrode active material 100. Also, it is preferable that the concentration of at least a part of nickel in the surface layer portion 100a is higher than the average nickel concentration of the entire positive electrode active material 100. Also, it is preferable that the concentration of at least a part of aluminum in the surface layer portion 100a is higher than the average aluminum concentration of the entire positive electrode active material 100. Also, it is preferable that the concentration of at least a part of fluorine in the surface layer portion 100a is higher than the average fluorine concentration of the entire positive electrode active material 100.

[0274] It is assumed that the surface and the surface layer portion 100a of the positive electrode active material 100 in one aspect of the present invention do not contain carbonates, hydroxy groups, etc. chemisorbed after the production of the positive electrode active material 100. It is also assumed that the electrolyte solution, binder, conductive material, or compounds derived therefrom attached to the surface of the positive electrode active material 100 are not included. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excessive oxygen, excessive fluorine, etc. that can be detected by surface analysis such as XPS. For example, in XPS, it is possible to separate the types of bonds by analysis, and corrections may be made to exclude C-F bonds derived from the binder.

[0275] Furthermore, before subjecting the sample to various analyses, in order to remove the electrolyte solution, binder, conductive material, or compounds derived therefrom attached to the surface of the positive electrode active material, the positive electrode active material and samples such as the positive electrode active material layer may be washed. At this time, lithium may dissolve in the solvent used for washing, etc., but even in such a case, since the added elements are difficult to dissolve out, it does not affect the atomic ratio of the added elements.

[0276] The concentration of the added element may also be compared in terms of the ratio to cobalt. By using the ratio to cobalt, it is possible to reduce the influence of carbonates and the like chemisorbed after the production of the positive electrode active material and make a comparison, which is preferable. For example, the atomic ratio Mg / Co of magnesium to cobalt by XPS analysis is preferably 0.400 or more and 1.20 or less, more preferably 0.500 or more and 1.00 or less, still more preferably 0.500 or more and 0.900 or less, and even more preferably 0.500 or more and 0.700 or less.

[0277] Also, for example, the atomic ratio Ni / Co of nickel to cobalt by XPS analysis is preferably 0.050 or more and 0.200 or less, more preferably 0.050 or more and 0.150 or less, still more preferably 0.050 or more and 0.100 or less, and even more preferably 0.050 or more and 0.070 or less.

[0278] Further, for example, the atomic ratio Al / Co of aluminum and cobalt by XPS analysis is preferably 0.010 or more and 0.100 or less, more preferably 0.010 or more and 0.050 or less, and even more preferably 0.010 or more and 0.040 or less.

[0279] Further, for example, the atomic ratio F / Mg of fluorine and magnesium by XPS analysis is preferably 0.100 or more and 1.00 or less, more preferably 0.100 or more and 0.800 or less, even more preferably 0.100 or more and 0.500 or less, even more preferably 0.100 or more and 0.300 or less, and even more preferably 0.100 or more and 0.200 or less.

[0280] The fact that it is in the above range indicates that these additive elements are not attached to a narrow range on the surface of the positive electrode active material 100, but are widely distributed at a preferable concentration in the surface layer portion 100a of the positive electrode active material 100. That is, as a result of the XPS analysis of the positive electrode active material 100, the fact that it is in the above range means that the crystal structure is less likely to collapse even when charging and discharging are repeated so that x becomes 0.24 or less, and excellent cycle characteristics can be realized. Further, good insertion and extraction of lithium are possible in the positive electrode active material 100, and excellent rate characteristics can be realized.

[0281] When performing XPS analysis, for example, monochromatized aluminum Kα rays can be used as the X-ray. Further, as the energy resolution, an XPS apparatus having an energy resolution such that the full width at half maximum of the Ag3d5 / 2 peak (112 eV) is 1.0 eV ± 0.1 eV in the XPS spectrum of the Ag sample is preferably used. Further, the take-off angle can be, for example, 45°. For example, it can be measured under the following XPS apparatus and measurement conditions. Measuring device: QuanteraII manufactured by PHI X-ray: Monochromatized Al Kα (1486.6 eV) Energy resolution: The full width at half maximum of the Ag3d5 / 2 peak is 1.0 eV ± 0.1 eV Detection area: 100 μmφ Detection depth: approximately 4 - 5 nm (extraction angle 45°) Measurement spectrum: wide scan, narrow scan for each detected element

[0282] When the cathode active material 100 of one embodiment of the present invention is subjected to XPS analysis, the peak (Mg1s peak) showing the binding energy between magnesium and other elements is preferably 1303.0 eV or more and less than 1305.0 eV, and more preferably about 1304.0 eV. This is a value different from the binding energy of magnesium fluoride, which is 1306.0 eV, and is a value close to the binding energy of magnesium oxide.

[0283] In the XPS analysis of the cathode active material 100 of one embodiment of the present invention, the measured XPS spectrum may be corrected so that the C1s peak is adjusted to a reference value (284.8 eV), that is, the entire spectrum is shifted. Thereby, the influence on XPS measurement due to machine differences of the XPS apparatus, differences in measurement conditions, etc. can be reduced.

[0284] Further, in the XPS analysis of the cathode active material 100 of one embodiment of the present invention, when analyzing the Mg1s peak to analyze the ratio of the peak component derived from the "O - Mg - O" bond, the peak component derived from the "O - Mg - F" bond, and the peak component derived from the "F - Mg - F" bond, it is preferable to have a peak component derived from the "O - Mg - O" bond. Further, the peak component derived from the "O - Mg - F" bond may be included, but it is preferably 30% or less, more preferably 20% or less, preferably 10% or less, and more preferably less than the detection limit of the total of the above three peak components. Further, the peak component derived from the "F - Mg - F" bond may be included, but it is preferably 10% or less of the total, and more preferably less than the detection limit.

[0285] That is, in the XPS analysis of the positive electrode active material 100 of one aspect of the present invention, when analyzing the ratio of the peak component derived from the "O-Mg-O" bond, the peak component derived from the "O-Mg-F" bond, and the peak component derived from the "F-Mg-F" bond, the peak component derived from the "O-Mg-O" bond is preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, and particularly preferably 100%.

[0286] The method for analyzing the Mg1s peak of the XPS spectrum in XPS analysis will be described. In the analysis of the Mg1s peak, the peak component derived from the O-Mg-O bond is defined as the fitting peak 1, the peak component derived from the O-Mg-F bond is defined as the fitting peak 2, and the peak component derived from the F-Mg-F bond is defined as the fitting peak 3. It is preferable to calculate the ratio of peak synthesis that minimizes the difference from the Mg1s peak of the XPS spectrum obtained by XPS analysis by synthesizing these three fitting peaks. At this time, the area ratio of the fitting peak 1, the fitting peak 2, and the fitting peak 3 can be output as the analysis result assuming that they are the abundance ratios of the O-Mg-O bond, the O-Mg-F bond, and the F-Mg-F bond.

[0287] In addition, in the above XPS spectrum analysis method, the energy value (Ep1) at the maximum value of the fitting peak 1 (also referred to as the peak top) can refer to the energy value at the maximum value of the Mg1s peak when MgO-coated LiCoO2 is separately measured as a standard sample. Also, the energy value (Ep3) at the maximum value of the fitting peak 3 can refer to the energy value at the maximum value of the Mg1s peak when magnesium fluoride (MgF2, for example, High Purity Chemical Laboratory MGH18XB, purity 99.9% (3N) up) is separately measured as a standard sample. Also, the energy value (Ep2) at the maximum value of the fitting peak 2 can be set to a value intermediate between Ep1 and Ep3. Also, Ep1 is located on the lower energy side compared to Ep3. Note that the energy value at the maximum value of the peak is also referred to as the peak position.

[0288] In the XPS analysis of the positive electrode active material 100 according to one embodiment of the present invention, it can be determined from the peak position and the full width at half maximum (FWHM) of the peak that the analysis result of the Mg1s peak is within the above preferred range. For example, the FWHM of the Mg1s peak is preferably 1.0 eV or more and 3.0 eV or less, more preferably 1.0 eV or more and 2.8 eV or less, and particularly preferably 1.0 eV or more and 2.6 eV or less. In addition, in the above, the peak position of the Mg1s peak is on the lower energy side than the energy value at the maximum value of the Mg1s peak when magnesium fluoride is separately measured as a standard sample.

[0289] <edx> It is preferable that one or more selected from the additive elements included in the positive electrode active material 100 have a concentration gradient. More preferably, the positive electrode active material 100 has different depths from the surface of the concentration peak due to the additive elements. The concentration gradient of the additive element can be evaluated, for example, by exposing the cross section of the positive electrode active material 100 with FIB (Focused Ion Beam) or the like and analyzing the cross section using EDX, EPMA (Electron Probe Microanalysis), or the like.

[0290] Among EDX measurements, the measurement while scanning within a region and the two-dimensional evaluation of the region is called EDX surface analysis. Also, the measurement while linearly scanning and the evaluation of the distribution of atomic concentration within the positive electrode active material is called line analysis. Further, in some cases, the data of a linear region extracted from the surface analysis of EDX is also called line analysis. Also, the measurement without scanning a certain region is called point analysis.

[0291] By EDX surface analysis (for example, element mapping), the concentration of the additive element in the surface layer portion 100a, the interior 100b, and the vicinity of the crystal grain boundary, etc. of the positive electrode active material 100 can be quantitatively analyzed. Also, by EDX line analysis, the concentration distribution and the maximum value of the additive element can be analyzed. Also, the analysis using a thinned sample like STEM-EDX can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction, and is more suitable.

[0292] Since the positive electrode active material 100 is a compound having a transition metal capable of inserting and extracting lithium and oxygen, the interface between the region where the transition metal M (for example, Co, Ni, Mn, Fe, etc.) and oxygen that are oxidized and reduced with the insertion and extraction of lithium exist and the region where they do not exist is taken as the surface of the positive electrode active material. When the positive electrode active material is subjected to analysis, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. As the protective film, a single-layer film or a multi-layer film such as carbon, metal, oxide, resin, etc. may be used.

[0293] In STEM-EDX analysis or the like, due to principles or measurement errors, the graph of the detected amount of characteristic X-rays of an element may not have a sharp change, making it difficult to precisely determine the surface. Therefore, when referring to the depth direction in STEM-EDX analysis or the like, the detected amount of characteristic X-rays of the transition metal M is the average value M of the detected amount of characteristic X-rays of the internal transition metal M AVE and the average value M of the detected amount of characteristic X-rays of the background transition metal M BG The point where the sum is 50%, or the detected amount of characteristic X-rays of oxygen is the average value O of the detected amount of characteristic X-rays of internal oxygen AVE and the average value O of the detected amount of characteristic X-rays of background oxygen BG The point where the sum is 50% is used as a reference point. If the point where the detected amount of characteristic X-rays of the transition metal M is 50% of the sum of the average value of the detected amount of characteristic X-rays of the internal transition metal M and the average value of the detected amount of characteristic X-rays of the background transition metal M is different from the point where the detected amount of characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of characteristic X-rays of internal oxygen and the average value of the detected amount of characteristic X-rays of background oxygen, it is considered to be affected by metal oxides, carbonates, etc. containing oxygen adhering to the surface. Therefore, the point where the detected amount of characteristic X-rays of the transition metal M is 50% of the sum of the average value M of the detected amount of characteristic X-rays of the internal transition metal M AVE and the average value M of the detected amount of characteristic X-rays of the background transition metal M BG The point where the sum is 50% can be adopted as a reference point. In the case of a positive electrode active material having a plurality of transition metals M, M of the transition metal element with the largest detected amount of characteristic X-rays inside AVE and M BG The reference point can be obtained using these.

[0294] The average value M of the detected amount of characteristic X-rays of the background transition metal M BG For example, it can be obtained by averaging the range of 2 nm or more, preferably 3 nm or more, outside the positive electrode active material while avoiding the vicinity where the detected amount of characteristic X-rays of the transition metal M starts to increase. Also, the average value M of the detected amount of characteristic X-rays of the internal transition metal M AVE It can be obtained by averaging the range of 2 nm or more, preferably 3 nm or more, in a region where the detected amounts of characteristic X-rays of the transition metal M and oxygen are saturated and stable, for example, in a portion that is 30 nm or more in depth, preferably more than 50 nm, from the region where the detected amount of characteristic X-rays of the transition metal M begins to increase. The average value O of the detected amount of characteristic X-rays of background oxygen BG and the average value O of the detected amount of characteristic X-rays of internal oxygen AVE can also be obtained in the same manner.

[0295] In addition, the surface of the positive electrode active material 100 in a cross-sectional STEM image or the like is the boundary between the region where an image derived from the crystal structure of the positive electrode active material is observed and the region where it is not observed, and is the outermost side of the region where an atomic column derived from the atomic nucleus of a metal element having an atomic number larger than that of lithium among the metal elements constituting the positive electrode active material is confirmed.

[0296] In addition, the peak in STEM-EDX line analysis refers to the convex maximum value that appears in the graph of the characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element. As for the noise in STEM-EDX line analysis, measurement values with a half-value width of the spatial resolution (R) or less, for example, R / 2 or less, can be considered.

[0297] The influence of noise can be reduced by scanning the same location multiple times under the same conditions. For example, the integrated value obtained by 2-scan measurement can be used as the detected value for each element. The number of scans is not limited to 2, and more scans can be performed and the average can be used as the detected value for each element.

[0298] STEM-EDX line analysis can be performed, for example, as follows. First, a protective film is deposited on the surface of the positive electrode active material. For example, carbon can be deposited using an ion sputtering apparatus (MC1000 manufactured by Hitachi High-Tech).

[0299] Next, the positive electrode active material is thinned to prepare a STEM cross-sectional sample. For example, thinning can be performed using a FIB-SEM apparatus (Hitachi High-Tech's XVision200TBS). At that time, pickup is performed with an MPS (Micro Probing System), and the conditions for finishing processing can be, for example, an acceleration voltage of 10 kV.

[0300] STEM-EDX line analysis can be performed using, for example, a STEM apparatus (Hitachi High-Tech's HD-2700), and as the EDX detector, EDAX's Octane T Ultra W can be used. As an example of the conditions for EDX line analysis using Hitachi High-Tech's HD-2700, the emission current of the STEM apparatus is set to be 6 μA or more and 10 μA or less, and a location with less depth and unevenness in the thinned sample is measured. Also, the magnification is, for example, about 150,000 times. The conditions for EDX line analysis can be with drift correction, a line width of 42 nm, a pitch of 0.2 nm, and 6 or more frames.

[0301] In order to increase the spatial resolution in STEM-EDX line analysis, it is preferable that the beam diameter of the electron beam (also referred to as the beam diameter, probe diameter, or probe diameter) is small. As the beam diameter in STEM-EDX line analysis, it is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. Also, in order to increase the analysis sensitivity in STEM-EDX line analysis, it is preferable to increase the beam current (also referred to as the probe current) of the electron beam. Therefore, the apparatus used for STEM-EDX line analysis preferably includes a spherical aberration correction device (Cs collector) that can reduce the beam diameter and increase the beam current.

[0302] In the case of the positive electrode active material 100 having magnesium and fluorine as additive elements, the distribution of fluorine preferably has a region overlapping with the distribution of magnesium. For example, the difference in the depth direction between the peak of the fluorine concentration or detected amount and the peak of the magnesium concentration or detected amount is preferably within 10 nm, more preferably within 3 nm, still more preferably within 1 nm, and even more preferably within 0.5 nm.

[0303] In the case of the positive electrode active material 100 having nickel as an additive element, the peak of the nickel concentration or detected amount in the surface layer portion 100a preferably exists on the surface of the positive electrode active material 100 or up to a depth of 3 nm from the reference point toward the center, and more preferably exists up to a depth of 1 nm. In the case of the positive electrode active material 100 having magnesium and nickel, the distribution of nickel preferably has a region overlapping with the distribution of magnesium. For example, the difference in the depth direction between the peak of the nickel concentration or detected amount and the peak of the magnesium concentration or detected amount is preferably within 3 nm, and more preferably within 1 nm.

[0304] When the positive electrode active material 100 has aluminum as an additive element, when EDX line analysis is performed, it is preferable that the peak of the concentration or detected amount of magnesium, nickel, or fluorine is closer to the surface than the peak of the concentration or detected amount of aluminum in the surface layer portion 100a. In other words, the peak of the concentration or detected amount of aluminum in the surface layer portion 100a is preferably on the inner side rather than the peak of the concentration or detected amount of magnesium, nickel, or fluorine. For example, the peak of the aluminum concentration or detected amount preferably exists on the surface of the positive electrode active material 100 or at a depth of 0.5 nm or more and 50 nm or less from the reference point toward the center, and more preferably exists at a depth of 5 nm or more and 50 nm or less.

[0305] Here, how to represent the positional relationship of the element distributions when performing EDX analysis will be described with reference to FIGS. 11(A) to 11(G). FIGS. 11(A) to 11(F) are schematic diagrams showing the concentration distributions or detection amount distributions of the first element e1 and the second element e2. Further, FIG. 11(G) is a schematic diagram showing the concentration distributions or detection amount distributions of the first element e1, the second element e2, and the third element e3.

[0306] For example, when the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is in the shape shown in FIG. 11(A), it is said that the position where the concentration or detection amount of the second element e2 is maximum is on the inner side of the position where the concentration or detection amount of the first element e1 is maximum. Also, for example, when the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is in the shape shown in FIG. 11(B), it is said that the position where the concentration or detection amount of the second element e2 is maximum is on the inner side of the position where the concentration or detection amount of the first element e1 is maximum. Also, for example, when the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is in the shape shown in FIG. 11(C), it is said that the position where the concentration or detection amount of the first element e1 is maximum is on the inner side of the position where the concentration or detection amount of the second element e2 is maximum. Also, for example, when the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is in the shape shown in FIG. 11(D), it is said that the position where the concentration or detection amount of the second element e2 is maximum is on the inner side of the position where the concentration or detection amount of the first element e1 is maximum. Also, for example, when the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is in the shape shown in FIG. 11(E), it is said that the position where the concentration or detection amount of the first element e1 is maximum is on the inner side of the position where the concentration or detection amount of the second element e2 is maximum. Also, for example, when the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is in the shape shown in FIG. 11(F), it is said that the position where the concentration or detection amount of the second element e2 is maximum is on the inner side of the position where the concentration or detection amount of the first element e1 is maximum.

[0307] Taking as an example the case where the concentration distributions or detection amount distributions of the first element e1, the second element e2, and the third element e3 have a positional relationship as shown in Fig. 11(G), an explanation will be given for the expression that there is a region where the distributions overlap. In this specification and the like, for two elements to have a region where their distributions overlap means, for example, that the position where the maximum value occurs in the concentration distribution or detection amount distribution of at least one of the elements is within the range where the concentration or detection amount is 1 / 5 or more of the maximum value in the concentration distribution or detection amount distribution of the other element. When the detection intensity of the background in EDX-ray analysis is 1 / 5 or more of the above-mentioned "maximum value", the "1 / 5 of the maximum value" in the above text shall be the "detection intensity of the background (also referred to as the detection lower limit)".

[0308] For example, in the case of the positional relationship shown in Fig. 11(G), the position (p2) where the maximum value occurs in the concentration distribution or detection amount distribution of the second element e2 is within the range where the concentration or detection amount is 1 / 5 (or the detection lower limit) or more of the maximum value in the concentration distribution or detection amount distribution of the first element e1 (the hatched region in the figure). Therefore, it is said that the first element e1 and the second element e2 have a region where their distributions overlap. Also, since the position (p3) where the maximum value occurs in the concentration distribution or detection amount distribution of the third element e3 is not within the range where the concentration or detection amount is 1 / 5 (or the detection lower limit) or more of the maximum value in the concentration distribution or detection amount distribution of the first element e1 (the hatched region in the figure), it cannot be said that the first element e1 and the third element e3 have a region where their distributions overlap.

[0309] Also, in the case of the positional relationship shown in Fig. 11(G), it can be said that the distributions of the second element e2 and the third element e3 are on the inner side of the distribution of the first element e1. Or, it can be said that the distributions of the second element e2 and the third element e3 are biased and exist on the inner side of the distribution of the first element e1.

[0310] <Powder resistivity measurement> The positive electrode active material 100 according to one aspect of the present invention has a stable crystal structure even at a high voltage. Since the crystal structure of the positive electrode active material is stable in the charged state, it is possible to suppress a decrease in charge-discharge capacity accompanying repeated charge-discharge. As a feature of the positive electrode active material 100 having the excellent characteristics as described above, the above-mentioned <xrd>In, Li x It was explained that when x in LiCoO2 is small, it has a crystal structure of the O3' type and / or the monoclinic O1(15) type. Also, the above-mentioned <edx>The preferable distribution of additive element A (e.g., Mg, Al, Ni) in the case of performing STEM-EDX analysis on the positive electrode active material 100 was described. Also, the above <xps>The preferred abundance of the additive element A (for example, Mg, Al, Ni) in the XPS analysis of the positive electrode active material 100 was described. Furthermore, the positive electrode active material 100 according to one embodiment of the present invention is also characterized by the volume resistivity of the powder.

[0311] As a characteristic of the positive electrode active material 100 according to one embodiment of the present invention, the volume resistivity of the powder of the positive electrode active material 100 is 1.0×10 8 Ω·cm or more and 1.0×10 10 Ω·cm or less at a pressure of 64 MPa. The positive electrode active material 100 having the above volume resistivity has a stable crystal structure even at a high voltage, and can be used as an index indicating that the surface layer portion 100a, which is important because the crystal structure of the positive electrode active material is stable in the charged state, can be formed well.

[0312] Also, the volume resistivity of the powder of the positive electrode active material 100 is 1.0×10 8 Ω·cm or more and 1.0×10 9 Ω·cm or less at a pressure of 64 MPa, more preferably 1.0×10 8 Ω·cm or more and 5.0×10 8 Ω·cm or less. The positive electrode active material 100 having the above volume resistivity has a stable crystal structure even at a high voltage, and can be used as an index indicating that the surface layer portion 100a, which is important because the crystal structure of the positive electrode active material is stable in the charged state, can be formed well, and can also be used as an index indicating that good insertion and extraction of lithium are possible in the positive electrode active material.

[0313] A method for measuring the volume resistivity of the powder of the positive electrode active material 100 according to one embodiment of the present invention will be described.

[0314] It is preferable that the measurement of the volume resistivity of the powder has a device part having terminals for resistance measurement and a mechanism for applying pressure to the powder to be measured. As the terminals for resistance measurement, it is preferable to have four terminals (also called four probes). As a measuring device having terminals for resistance measurement and a mechanism for applying pressure to the powder (sample) to be measured, for example, MCP-PD600 manufactured by Nitto Seiko Analytic Co., Ltd. can be used. For the device part of the four-probe method, Loresta-GXII or Hi-Loresta-UX can be used. Loresta-GXII can be used for measuring low-resistance samples, and Hi-Loresta-UX can be used for measuring high-resistance samples. Note that as the measurement environment, it is preferable to be a stable environment such as a dry room. As the environment of the dry room, for example, a temperature environment of 25°C and a dew point environment of -40°C or lower are preferable.

[0315] The measurement of the volume resistivity of the powder using the measuring device shown above will be described. First, the powder sample is set in the measuring unit. In the measuring unit, the structure is such that the powder sample and the terminals for resistance measurement are in contact, and it is possible to apply pressure to the powder sample. Also, it has a structure for measuring the volume of the powder sample in the measuring unit. Specifically, the above-mentioned measuring unit has a cylindrical space, and the powder sample is set in this space. The structure for measuring the volume of the powder sample described above can measure the volume occupied by the powder at that time by measuring the height of the powder set in the space.

[0316] In the measurement of the volume resistivity of the powder, with pressure applied to the powder, the electrical resistance measurement of the powder and the volume measurement of the powder are carried out. The pressure applied to the powder can be carried out under multiple conditions. For example, at each pressure condition of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa, the electrical resistance of the powder and the volume of the powder can be measured. From the measured values of the electrical resistance and volume of the powder, the volume resistivity of the powder can be calculated.

[0317] When performing the measurement as described above, the volume resistivity of the powder of the positive electrode active material 100 of one embodiment of the present invention is 1.0×10 8 Ω·cm or more and 1.0×10 10 Ω·cm or less, it shows favorable cycle characteristics in the charge-discharge cycle test under high voltage conditions. When it is 1.0×10 8 Ω·cm or more and 1.0×10 9 Ω·cm or less, it shows favorable cycle characteristics in the charge-discharge cycle test under high voltage conditions and also shows favorable discharge characteristics in the discharge rate test. When the above volume resistivity is 1.0×10 8 Ω·cm or more and 5.0×10 8 Ω·cm or less, it shows even more favorable discharge characteristics in the discharge rate test.

[0318] <epma> The concentration of the additive element in the positive electrode active material 100 can be analyzed using EDX, but it can also be analyzed using EPMA. EPMA has a higher detection ability (also referred to as a lower detection limit) than EDX in the analysis of elements present in trace amounts in a sample. Therefore, it is preferable to use EPMA when analyzing a region where the additive element is present in trace amounts.

[0319] In the EPMA analysis, the cross-section of the positive electrode active material 100 is exposed by mechanical polishing, ion polishing, FIB, etc., and the cross-section is analyzed. As an EPMA apparatus, for example, the electron probe microanalyzer JXA-iHP200F manufactured by JEOL Ltd. can be used.

[0320] Since EPMA uses a wavelength-dispersive detector, it has a higher ability to detect trace elements compared to EDX that uses an energy-dispersive detector. On the other hand, the spatial resolution in the EPMA analysis is inferior compared to EDX (especially STEM-EDX). Therefore, STEM-EDX is suitable for analysis focusing on the detailed distribution of the additive element in the surface layer portion 100a of the positive electrode active material 100, and the EPMA analysis is suitable for analysis of trace additive elements in the interior 100b. Note that since EPMA and EDX have different analysis methods, the concentration values obtained when analyzing the same region by each analysis method may not match.

[0321] <Microelectron diffraction pattern> Similar to Raman spectroscopy, it is preferable that the characteristics of the rock-salt type crystal structure are also observed in the microelectron diffraction pattern together with the crystal structure of the layered rock salt. However, in the STEM image and the microelectron diffraction pattern, taking into account the above-mentioned difference in sensitivity, it is preferable that the characteristics of the rock-salt type crystal structure do not become too strong in the surface layer portion 100a, especially the outermost surface (for example, a depth of 1 nm from the surface). This is because having the additive element such as magnesium present in the lithium layer while maintaining the layered rock salt type crystal structure can ensure the diffusion path of lithium and has a stronger function of stabilizing the crystal structure than having the outermost surface covered with the rock-salt type crystal structure.

[0322] Therefore, for example, when obtaining the ultramicro electron diffraction pattern of a region with a depth of 1 nm or less from the surface and the ultramicro electron diffraction pattern of a region with a depth of 3 nm or more and 10 nm or less, it is preferable that the difference in lattice constants calculated from these is small.

[0323] For example, the difference in lattice constants calculated from the measurement location with a depth of 1 nm or less from the surface and the measurement location with a depth of 3 nm or more and 10 nm or less is preferably 0.1×10 -10 m or less for the a-axis, and preferably 1.0×10 -10 m or less for the c-axis. Further, it is more preferably 0.03×10 -10 m or less for the a-axis, and more preferably 0.6×10 -10 m or less for the c-axis. Further, it is even more preferably 0.04×10 -10 m or less for the a-axis, and even more preferably 0.3×10 -10 m or less for the c-axis.

[0324] <Second positive electrode active material> The positive electrode of one embodiment of the present invention can have, in addition to the positive electrode active material 100, a second positive electrode active material different from the positive electrode active material 100. Similar to the positive electrode active material 100, the second positive electrode active material 200 has a function of taking in lithium ions and a function of releasing them during charge and discharge. As the second positive electrode active material 200 used in one embodiment of the present invention, a material that is the same as the positive electrode active material 100 except for having a different particle size and has little deterioration during charging and discharging (hereinafter also referred to as "charge and discharge") even at a high charging voltage can be used. Specifically, in the method for producing the positive electrode active material described in Embodiment 1, a positive electrode active material (composite oxide) having a particle size (median diameter (D50)) of 0.1 μm or more and less than 9 μm, preferably 1 μm or more and 5 μm or less, obtained by reducing the particle size of the starting material and lowering the temperature or shortening the heat treatment time can be used. Similar to the positive electrode active material 100 described above, the second positive electrode active material 200 preferably contains any one or more of the additive element X, additive element Y, and additive element Z.

[0325] The content of this embodiment can be freely combined with the content of other embodiments.

[0326] (Embodiment 3) In this embodiment, each element constituting the battery will be described.

[0327] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material, and may further have at least one of a conductive material and a binder. As the positive electrode active material, the positive electrode active material 100 described in Embodiment 1 and Embodiment 2 can be used.

[0328] As the positive electrode current collector, for example, a metal foil can be used. The positive electrode can be formed by applying a slurry onto the metal foil and drying it. Note that pressing may be applied after drying. The positive electrode is formed by forming an active material layer on the positive electrode current collector.

[0329] The slurry is a material liquid used to form an active material layer on the positive electrode current collector, and contains an active material, a binder, and a solvent, and preferably further contains a conductive material mixed therein. Note that the slurry may also be referred to as an electrode slurry or an active material slurry, and when forming a positive electrode active material layer, it may be referred to as a positive electrode slurry, and when forming a negative electrode active material layer, it may be referred to as a negative electrode slurry.

[0330] The positive electrode active material has a function of taking in and releasing lithium ions during charge and discharge. As the positive electrode active material 100 used as one aspect of the present invention described above, a material with a high charging voltage and little deterioration during charge and discharge can be used.

[0331] [Binder] 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, fluorine rubber can be used as the binder.

[0332] Also, as the binder, it is preferable to use, for example, a water-soluble polymer. As the water-soluble polymer, for example, polysaccharides can be used. As the polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, or starch can be used. Further, it is more preferable to use these water-soluble polymers in combination with the above-described rubber material.

[0333] Alternatively, as the binder, materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose are preferably used.

[0334] A plurality of the above binders may be used in combination.

[0335] For example, a material having a particularly excellent viscosity adjustment effect may be used in combination with other materials. For example, although rubber materials and the like are excellent in adhesive force and elastic force, it 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-described polysaccharides, for example, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, or starch can be used.

[0336] Cellulose derivatives such as carboxymethyl cellulose can be made into salts such as sodium salts or ammonium salts of carboxymethyl cellulose, for example, to increase their solubility and facilitate the exertion of their effect as a viscosity modifier. By increasing the solubility, the dispersibility with the active material or other components can also be enhanced when preparing the electrode slurry. In this specification and the like, cellulose and cellulose derivatives used as the electrode binder shall include their salts.

[0337] Water-soluble polymers can stabilize the viscosity by dissolving in water and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, in an aqueous solution. Also, due to having functional groups, they are expected to be easily adsorbed stably on the surface of the active material. Further, cellulose derivatives such as carboxymethyl cellulose have many materials having functional groups such as hydroxyl groups or carboxyl groups, and due to having functional groups, it is expected that the polymers interact with each other and exist covering the surface of the active material widely.

[0338] When the binder covering the surface of the active material or in contact with the surface forms a film, it is also expected to play a role as a passive film and suppress the decomposition of the electrolyte. Here, the "passive film" is a film having no electrical conductivity or a film having extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Further, it is more desirable that the passive film suppresses electrical conductivity while allowing lithium ions to conduct.

[0339] <Conductive material> The conductive material, also called a conductivity-imparting agent or a conductivity aid, is a carbon material. By attaching the conductive material between a plurality of active materials, the plurality of active materials are electrically connected to each other, enhancing the conductivity. Note that "attachment" does not only refer to the physical adhesion between the active material and the conductive material, but also includes cases where a covalent bond occurs, cases where bonding occurs by van der Waals forces, cases where a part of the surface of the active material is covered by the conductive material, cases where the conductive material fits into the surface irregularities of the active material, and cases where they are electrically connected even if they are not in contact with each other.

[0340] Active material layers such as the positive electrode active material layer and the negative electrode active material layer preferably have a conductive material.

[0341] As the conductive material, for example, any one or two or more of carbon blacks such as acetylene black and furnace black, graphites such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds can be used.

[0342] As the carbon fiber, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. Also, as the carbon fiber, carbon nanofibers or carbon nanotubes can be used. Carbon nanotubes can be produced, for example, by a vapor phase growth method.

[0343] In this specification and the like, the graphene compound includes graphene, multilayer graphene, multi-graphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. The graphene compound refers to a material that contains carbon, has a flat or sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may also be referred to as a carbon sheet. The graphene compound may have a functional group. Also, the graphene compound preferably has a bent shape. Also, the graphene compound may be curled to be like a carbon nanofiber.

[0344] The content of the conductive material 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.

[0345] Unlike granular conductive materials such as carbon black that make point contact with the active material, the graphene compound enables surface contact with low contact resistance. Therefore, the electrical conductivity between the granular active material and the graphene compound can be improved with a smaller amount than that of ordinary conductive materials. Thus, the ratio of the active material in the active material layer can be increased. Thereby, the discharge capacity of the battery can be increased.

[0346] Particulate carbon-containing compounds such as carbon black and graphite, or fibrous carbon-containing compounds such as carbon nanotubes are likely to enter minute spaces. The minute spaces refer to, for example, the regions between a plurality of active materials. By using a combination of a carbon-containing compound that easily enters minute spaces and a sheet-like carbon-containing compound such as graphene that can impart conductivity over a plurality of particles, the density of the electrode can be increased and an excellent conductive path can be formed. The battery obtained by the manufacturing method of one embodiment of the present invention can have a high capacity density and stability, and is effective as a vehicle-mounted battery.

[0347] <Positive current collector> As the 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. Further, an aluminum alloy added with elements for improving heat resistance such as silicon, titanium, neodymium, scandium, molybdenum can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts 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, punching metal, expanded metal, etc. The current collector preferably has a thickness of 5 μm or more and 30 μm or less.

[0348] [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 has a negative electrode active material and may further have a conductive material and a binder.

[0349] [Negative electrode active material] As the negative electrode active material, for example, an alloy-based material or a carbon material can be used.

[0350] In addition, as the negative electrode active material, an element capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger capacity compared to carbon, and 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, there are SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. 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.

[0351] In this specification, etc., "SiO" refers to, for example, silicon monoxide. Alternatively, SiO can also be represented as SiO x where x preferably has a value of 1 or 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.

[0352] As the carbon material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon fiber (carbon nanotube), graphene, carbon black, etc. may be used.

[0353] Examples of graphite include artificial graphite or natural graphite, etc. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. Here, as artificial graphite, spherical graphite having a spherical shape can be used. For example, MCMB may have a spherical shape, which is preferable. Also, MCMB can relatively easily reduce its surface area, which may be preferable. Examples of natural graphite include flaky graphite, spheroidized natural graphite, etc.

[0354] Graphite exhibits a potential as low as that of metallic lithium (0.05 V or more and 0.3 V or less vs. Li / Li + ) when lithium ions are inserted into it (when forming a lithium-graphite intercalation compound). As a result, lithium-ion batteries using graphite 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 metallic lithium, so it is preferable.

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

[0356] In addition, as the negative electrode active material, Li 3-x M x N (M = Co, Ni, Cu) having an Li3N-type structure, which is a nitride of lithium and a transition metal, can be used. For example, Li 2.6 Co 0.4 N exhibits a large discharge capacity (900 mAh / g, 1890 mAh / cm 3 ) and is preferable.

[0357] When using a nitride of lithium and a transition metal, since lithium ions are contained in the negative electrode active material, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when using a material containing lithium ions as the positive electrode active material, a nitride of lithium and a transition metal can be used as the negative electrode active material by previously desorbing the lithium ions contained in the positive electrode active material.

[0358] In addition, materials that undergo conversion reactions can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Materials that undergo conversion reactions further include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, CoS 0.89 , sulfides such as NiS, CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.

[0359] As another form of the negative electrode, it may be a negative electrode without a negative electrode active material at the end of battery fabrication. As a negative electrode without a negative electrode active material, for example, a negative electrode having only a negative electrode current collector at the end of battery fabrication, where lithium ions desorbed from the positive electrode active material during battery charging are deposited as lithium metal on the negative electrode current collector to form a negative electrode active material layer, can be used. A battery using such a negative electrode may be called a negative electrode-free (anode-free) battery, a negative electrode-less (anode-less) battery, and the like.

[0360] When using a negative electrode without a negative electrode active material, it may have a film for uniformizing the deposition of lithium on the negative electrode current collector. As a film for uniformizing the deposition of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As the solid electrolyte, sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes can be used. Among them, polymer-based solid electrolytes are relatively easy to form a uniform film on the negative electrode current collector, so they are suitable as a film for uniformizing the deposition of lithium. In addition, as a film for uniformizing the deposition of lithium, for example, a metal film that forms an alloy with lithium can be used. As a metal film that forms an alloy with lithium, for example, a magnesium metal film can be used. Since lithium and magnesium form a solid solution in a wide composition range, it is suitable as a film for uniformizing the deposition of lithium.

[0361] In addition, when using a negative electrode without a negative electrode active material, a negative electrode current collector having irregularities can be used. When using a negative electrode current collector having irregularities, since the concave portion of the negative electrode current collector becomes a cavity where lithium possessed by the negative electrode current collector is likely to precipitate, it is possible to suppress the formation of a dendrite shape when lithium precipitates.

[0362] As the conductive material and binder that the negative electrode active material layer can have, the same materials as those of the conductive material and binder that the positive electrode active material layer can have can be used.

[0363] <Negative electrode current collector> In addition to the same materials as those of the positive electrode current collector, copper or the like can also be used for the negative electrode current collector. It is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0364] [Electrolyte] The secondary battery has an electrolyte containing carrier ions. In this specification and the like, the electrolyte is not limited to those containing an organic solvent that is liquid at room temperature, and includes a solid electrolyte, and also includes an electrolyte (semi-solid electrolyte) containing both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature. Note that a solution in which a lithium salt is dissolved in an organic solvent that is liquid at room temperature may be referred to as an electrolytic solution.

[0365] <Organic solvent that is liquid at room temperature> An example of an organic solvent that is liquid at room temperature will be described below.

[0366] The organic solvent that is liquid at room temperature is preferably an aprotic organic solvent. For example, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used.

[0367] By using one or more ionic liquids (room temperature molten salts) that are flame-retardant and have low volatility as the organic solvent that is liquid at room temperature, even if the internal temperature rises due to internal short circuit or overcharge of the battery cell, rupture and ignition of the battery cell can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation used in the organic solvent include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, or aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the organic solvent include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions.

[0368] In addition, examples of the lithium salt dissolved in the above organic solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12 One or more selected from LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), and LiN(C2F5SO2)2, etc. can be used.

[0369] <Additive> The above organic solvent may have an additive. The additive can suppress the reaction decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when operating the secondary battery at high voltage and / or high temperature. As the additive, for example, vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB) may be used. LiBOB is particularly preferred because it easily forms a good film. VC or FEC is preferred because it can form a good film on the negative electrode during the aging of the secondary battery or during the charging at the initial stage of use, improving the cycle characteristics.

[0370] As the additive, a compound represented by the following general formula (G1) may be included. The following general formula (G1) is a compound having two cyano groups and can be called a dinitrile compound.

[0371]

Chemical formula

[0372] In the above general formula (G1), R represents a hydrocarbon having 1 to 5 carbon atoms. Preferably, in the above general formula (G1), R represents a hydrocarbon having 2 to 4 carbon atoms.

[0373] Specific examples of the above general formula (G1) include, for example, succinonitrile, glutaronitrile, adiponitrile (ADN), or ethylene glycol bis(propionitrile) ether (EGBE).

[0374] The structural formula (H1) of succinonitrile is shown below.

[0375] [Chemistry]

[0376] The structural formula (H2) of glutaronitrile is shown below.

[0377] [Chemistry]

[0378] The structural formula (H3) of adiponitrile is shown below.

[0379] [Chemistry]

[0380] The structural formula (H4) of ethylene glycol bis(propionitrile) ether is shown below.

[0381] [Chemistry]

[0382] As an additive, any one or more of dinitrile compounds can be used.

[0383] Furthermore, fluorobenzene may be added to the above organic solvent. The concentration of the additive can be, for example, 0.1 wt% or more and 5 wt% or less based on the whole electrolyte solution. PS or EGBE can form a good film on the positive electrode during charge and discharge and can improve the cycle characteristics, which is preferable. FB is preferable because it improves the wettability of the organic solvent to the positive and negative electrodes. The dinitrile compound can improve the high voltage resistance because the nitrile group is oriented to the positive and negative electrodes to inhibit the oxidative decomposition of the organic solvent. Furthermore, the dinitrile compound can prevent the dissolution of copper during over-discharge when a current collector having copper is used for the negative electrode, which is preferable. Considering the use of the secondary battery at high voltage, it is preferable to add a nitrile compound.

[0384] It is not necessary to be liquid at room temperature, and a semi-solid material called a polymer gel electrolyte may be used as the organic solvent. By using a polymer gel electrolyte, the safety against leakage and the like is enhanced. In addition, the battery cell can be made thinner and lighter.

[0385] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, gel of fluorine-based polymer, etc. can be used.

[0386] 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. Further, the formed polymer may have a porous shape.

[0387] [Separator] When the electrolyte contains an electrolytic solution, a separator is disposed between the positive electrode and the negative electrode. As the separator, for example, those formed of fibers having cellulose such as paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into a bag shape and disposed so as to wrap either the positive electrode or the negative electrode.

[0388] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a hydroxide material, a fluorine material, a polyamide material, or a mixture thereof. As the ceramic material, for example, aluminum oxide particles, silicon oxide particles, magnesium oxide, etc. can be used. As the hydroxide material, magnesium hydroxide, aluminum hydroxide, etc. can be used. As the fluorine material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0389] Coating with a ceramic material improves oxidation resistance, thus suppressing deterioration of the separator during high-voltage charging and improving the reliability of the secondary battery. Also, coating with a fluorine material makes it easier for the separator and the electrode to adhere, improving the output characteristics. Coating with a polyamide material, especially aramid, improves heat resistance, thus improving the safety of the secondary battery.

[0390] 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 material may be coated on the surface that contacts the negative electrode.

[0391] Using a separator with a multilayer structure can maintain the safety of the secondary battery even if the overall thickness of the separator is thin, so the capacity per unit volume of the secondary battery can be increased.

[0392] [Outer package] As the exterior body of the battery, for example, metal materials such as aluminum, stainless steel, and titanium, or resin materials can be used. Also, a film-shaped exterior body can be used. As the film, for example, on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, and polyamide, a metal thin film or metal foil with excellent flexibility such as aluminum, stainless steel, titanium, copper, and nickel is provided, and 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 structure film can be used. Such a multi-layer structure film can be called a laminate film. At this time, using the material name of the metal layer of the laminate film, it may be called an aluminum (aluminum) laminate film, a stainless steel laminate film, a titanium laminate film, a copper laminate film, a nickel laminate film, etc.

[0393] The material or thickness of the metal layer of the laminate film may affect the flexibility of the battery. As an exterior body used for a battery that emphasizes flexibility or weight reduction, for example, it is preferable to use an aluminum laminate film having a polypropylene layer, an aluminum layer, and a nylon layer. Here, as the thickness of the aluminum layer, 50 μm or less is preferable, 40 μm or less is more preferable, 30 μm or less is more preferable, and 20 μm or less is more preferable. In addition, when the aluminum layer is thinner than 10 μm, since there is concern about a decrease in gas barrier properties due to pinholes in the aluminum layer, it is desirable that the thickness of the aluminum layer is 10 μm or more.

[0394] For example, as an exterior body used for a battery that emphasizes physical strength or safety, it is preferable to use a stainless steel laminate film having a polypropylene layer, a stainless steel layer, and a nylon layer. Further, a polyethylene terephthalate layer may be provided on the nylon layer. Here, the thickness of the stainless steel layer is preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and even more preferably 20 μm or less. Note that when the stainless steel layer is thinner than 10 μm, there is a concern about a decrease in gas barrier properties due to pinholes in the stainless steel layer. Therefore, the thickness of the stainless steel layer is desirably 10 μm or more. Note that the stainless steel in this specification refers to steel (an alloy of iron and carbon) containing about 12% or more of chromium, and can be roughly classified into a martensitic type, a ferritic type, or an austenitic type in terms of composition. Note that it also includes stainless steel to which one or more elements selected from Ti, Nb, Mo, Cu, Ni, or Si are added.

[0395] Alternatively, for example, it is preferable to use a titanium laminate film having a polypropylene layer, a titanium layer, and a nylon layer. Further, a polyethylene terephthalate layer may be provided on the nylon layer. Here, the thickness of the titanium layer is preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and even more preferably 20 μm or less. Note that when the titanium layer is thinner than 10 μm, there is a concern about a decrease in gas barrier properties due to pinholes in the titanium layer. Therefore, the thickness of the titanium layer is desirably 10 μm or more.

[0396] The content of this embodiment can be freely combined with the content of other embodiments.

[0397] (Embodiment 4) In this embodiment, an example of the shape of a secondary battery having a positive electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0398] [Coin-type secondary battery] An example of a coin-shaped secondary battery will be described. FIG. 12(A) is an exploded perspective view of a coin-shaped (single-layer flat type) secondary battery, FIG. 12(B) is an external view, and FIG. 12(C) is a cross-sectional view thereof. The coin-shaped secondary battery is mainly used for small electronic devices.

[0399] In addition, in FIG. 12(A), for clarity, it is a schematic diagram so that the overlapping (vertical relationship and positional relationship) of the members can be understood. Therefore, FIGS. 12(A) and 12(B) are not completely corresponding diagrams that match exactly.

[0400] In FIG. 12(A), the positive electrode 304, the separator 310, the negative electrode 307, the spacer 322, and the washer 312 are stacked. These are sealed with the negative electrode can 302, the positive electrode can 301, and a gasket. Note that in FIG. 12(A), the gasket for sealing is not shown. The spacer 322 and the washer 312 are used to protect the inside or fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0401] A laminated structure in which a positive electrode active material layer 306 is formed on the positive electrode current collector 305 is used as the positive electrode 304.

[0402] FIG. 12(B) is a perspective view of the completed coin-shaped secondary battery.

[0403] The coin-shaped 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 with 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. 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. The negative electrode 307 is not limited to a laminated structure, and a lithium metal foil or an alloy foil of lithium and aluminum may be used.

[0404] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-shaped secondary battery 300, the active material layer may be formed on only one side.

[0405] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys thereof or alloys of these and other metals (e.g., stainless steel, etc.) can be used. Also, in order to prevent corrosion by the electrolyte or the like, it is preferable to coat with nickel or 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.

[0406] These negative electrode 307, positive electrode 304, and separator 310 are immersed in the electrolyte, and as shown in Fig. 12(C), 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-shaped secondary battery 300.

[0407] By having the above configuration, a coin-shaped secondary battery 300 with a high discharge capacity and excellent cycle characteristics can be obtained.

[0408] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 13(A). As shown in Fig. 13(A), the cylindrical secondary battery 616 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 601 and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0409] Fig. 13(B) is a diagram schematically showing a cross-section of the cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 13(B) 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.

[0410] 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 central axis. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys thereof, or alloys of these and other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat the battery can 602 with nickel and 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 insulating plate 609. Further, a non-aqueous electrolytic solution (not shown) is injected into the interior of the battery can 602 in which the battery element is provided. As the non-aqueous electrolytic solution, the same one as that used in a coin-type secondary battery can be used.

[0411] Since the positive and negative electrodes used in the cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector.

[0412] By using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0413] 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. A metal material such as aluminum can be used for the positive electrode terminal 603 and the negative electrode terminal 607. The positive electrode terminal 603 is resistance welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602, respectively. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold value. Further, the PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it limits the current amount due to the increase in resistance to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO3)-based semiconductor ceramics or the like can be used.

[0414] FIG. 13(C) shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to a conductor 624 separated by an insulator 625. The conductor 624 is electrically connected to a control circuit 620 via a wiring 623. Further, the negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via a wiring 626. As the control circuit 620, a charge / discharge control circuit that performs charge / discharge or the like, or a protection circuit that prevents overcharge and / or overdischarge can be applied.

[0415] FIG. 13(D) shows an example of the power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, and the plurality of secondary batteries 616 are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by a wiring 627. The plurality of secondary batteries 616 may be connected in parallel, may be connected in series, or may be connected in parallel and then further connected in series. By configuring the power storage system 615 having a plurality of secondary batteries 616, a large amount of power can be extracted.

[0416] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0417] Also, a temperature control device may be provided between the plurality of secondary batteries 616. When the secondary battery 616 is overheated, it can be cooled by the temperature control device, and when the secondary battery 616 is too cold, it can be heated by the temperature control device. Therefore, the performance of the power storage system 615 is less likely to be affected by the outside air temperature.

[0418] Also, in FIG. 13(D), the power storage system 615 is electrically connected to the control circuit 620 via the wiring 621 and the wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 616 via the conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 via the conductive plate 614.

[0419] [Another Structural Example of Secondary Battery] A structural example of the secondary battery will be described with reference to FIGS. 14 and 15.

[0420] The secondary battery 913 shown in FIG. 14(A) has a wound body 950 in which a terminal 951 and a terminal 952 are provided inside a housing 930. The wound body 950 is immersed in the 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. 14(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 terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (for example, aluminum or the like) or a resin material can be used.

[0421] Note that, as shown in FIG. 14(B), the housing 930 shown in FIG. 14(A) may be formed of a plurality of materials. For example, the secondary battery 913 shown in FIG. 14(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.

[0422] As the housing 930a, an insulating material can be used. In particular, by using a material such as an organic resin for the surface on which the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna may be provided inside the housing 930a. As the housing 930b, for example, a metal material can be used.

[0423] Furthermore, the structure of the wound body 950 is shown in FIG. 14(C). The wound body 950 includes a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0424] Also, a secondary battery 913 having a wound body 950a as shown in FIG. 15 may be used. The wound body 950a shown in FIG. 15(A) includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0425] By using the positive electrode active material 100 described in Embodiment 1, 2, etc. for the positive electrode 932, a secondary battery 913 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0426] The separator 933 has a width wider than that of the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Also, it is preferable in terms of safety that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Also, a wound body 950a having such a shape is preferable in terms of safety and productivity.

[0427] As shown in FIG. 15(B), the negative electrode 931 is electrically connected to the terminal 951 by ultrasonic bonding, welding, or crimping. The terminal 951 is electrically connected to the terminal 911a. Also, the positive electrode 932 is electrically connected to the terminal 952 by ultrasonic bonding, welding, or crimping. The terminal 952 is electrically connected to the terminal 911b.

[0428] As shown in FIG. 15(C), the wound body 950a and the electrolytic solution are covered by the housing 930 to form the secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc. in the housing 930. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure in order to prevent battery rupture.

[0429] As shown in FIG. 15(B), the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, a secondary battery 913 with a larger discharge capacity can be obtained. For other elements of the secondary battery 913 shown in FIGS. 15(A) and (B), reference can be made to the description of the secondary battery 913 shown in FIGS. 14(A) to (C).

[0430] <Laminated secondary battery> Next, an example of a laminated secondary battery is shown in FIGS. 16(A) and 16(B) as an example of an external view. FIGS. 16(A) and 16(B) 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.

[0431] FIG. 17(A) shows an external view of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, 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 a 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. Also, the negative electrode 506 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region. Note that the area or shape of the tab regions of the positive electrode and the negative electrode is not limited to the example shown in FIG. 17(A).

[0432] <Method for manufacturing a laminated secondary battery> An example of a method for manufacturing a laminated secondary battery whose external view is shown in Fig. 16(A) will be described with reference to Figs. 17(B) and 17(C).

[0433] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. Fig. 17(B) shows the laminated negative electrode 506, separator 507, and positive electrode 503. Here, an example in which five sets of negative electrodes and four sets of positive electrodes are used is shown. It can also be called a laminate composed of a negative electrode, a separator, and a positive electrode. Next, the tabs of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like can be used. Similarly, the tabs of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0434] Next, the negative electrode 506, the separator 507, and the positive electrode 503 are arranged on the exterior body 509.

[0435] Next, as shown in Fig. 17(C), the exterior body 509 is bent at the portion indicated by the broken line. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like can be used. At this time, a region that is not joined to a part (or one side) of the exterior body 509 (hereinafter referred to as an inlet) is provided so that the electrolyte can be introduced later.

[0436] Next, the electrolyte is introduced into the interior of the exterior body 509 through the inlet provided in the exterior body 509. The introduction of the electrolyte is preferably performed under a reduced pressure atmosphere or an inert atmosphere. And finally, the inlet is joined. In this way, the laminated secondary battery 500 can be manufactured.

[0437] By using the positive electrode active material 100 described in Embodiment 1, 2, etc. for the positive electrode 503, a secondary battery 500 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0438] [Example of a battery pack] An example of a secondary battery pack according to one aspect of the present invention capable of wireless charging using an antenna will be described with reference to FIG. 18.

[0439] FIG. 18(A) is a view showing the appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (which can also be called a thick flat plate shape). FIG. 18(B) is a view for explaining the configuration of the secondary battery pack 531. The secondary battery pack 531 includes a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0440] The inside of the secondary battery 513 may have a structure having a wound body or a structure having a laminate.

[0441] In the secondary battery pack 531, for example, as shown in FIG. 18(B), it has a control circuit 590 on the circuit board 540. The circuit board 540 is electrically connected to a terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0442] Alternatively, as shown in FIG. 18(C), it may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via a terminal 514.

[0443] Note that the antenna 517 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. Alternatively, the antenna 517 may use a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. That is, the antenna 517 may be made to function as one of the two conductors of a capacitor. Thereby, power exchange can be performed not only by an electromagnetic field and a magnetic field but also by an electric field.

[0444] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding the electromagnetic field by the secondary battery 513. As the layer 519, for example, a magnetic material can be used.

[0445] The content of the present embodiment can be freely combined with the content of other embodiments.

[0446] (Embodiment 5) In the present embodiment, an example of a vehicle having a secondary battery according to an aspect of the present invention is shown.

[0447] Typically, a secondary battery can be applied to an automobile as the vehicle. Examples of the automobile include next-generation clean energy vehicles such as a hybrid vehicle (HV), an electric vehicle (EV), or a plug-in hybrid vehicle (also referred to as PHEV or PHV), and a secondary battery can be applied as one of the power sources mounted on the automobile. The vehicle is not limited to an automobile. For example, examples of the vehicle include a train, a monorail, a ship, a submarine (a deep-sea exploration submarine, an unmanned submarine), an aircraft (a helicopter, an unmanned aerial vehicle (drone), an airplane, a rocket, a satellite), an electric bicycle, and an electric motorcycle, and a secondary battery according to an aspect of the present invention can be applied to these vehicles.

[0448] In the electric vehicle, as shown in FIG. 19(C), first batteries 1301a and 1301b are provided as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304 is installed. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to be able to output high power, and a large capacity is not so necessary, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0449] The internal structure of the first battery 1301a may be a wound type shown in FIG. 14(C) or FIG. 15(A), or may be a laminated type shown in FIG. 16(A) or FIG. 16(B).

[0450] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having a plurality of secondary batteries, a large amount of power can be extracted. The plurality of secondary batteries may be connected in parallel, may be connected in series, or may be connected in parallel and then further connected in series. The plurality of secondary batteries are also referred to as a battery assembly.

[0451] Also, in an in-vehicle secondary battery, in order to cut off the power from a plurality of secondary batteries, it has a service plug or a circuit breaker that can cut off a high voltage without using tools, and is provided in the first battery 1301a.

[0452] Also, the power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but supplies power to 42V in-vehicle components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DCDC circuit 1306. Even when the rear wheels have a rear motor 1317, the first battery 1301a is used to rotate the rear motor 1317.

[0453] Also, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power window 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0454] Next, the first battery 1301a will be described with reference to FIG. 19(A).

[0455] FIG. 19(A) shows an example in which nine rectangular secondary batteries 1300 are used as one battery pack 1415. Also, the nine rectangular secondary batteries 1300 are connected in series, one electrode is fixed by a fixing portion 1413 made of an insulator, and the other electrode is fixed by a fixing portion 1414 made of an insulator. In the present embodiment, an example of fixing by the fixing portions 1413 and 1414 is shown, but it may be configured to be housed in a battery housing box (also referred to as a casing). Since the vehicle is assumed to be subjected to vibrations or shakes from the outside (such as a road surface), it is preferable to fix a plurality of secondary batteries by the fixing portions 1413 and 1414 and the battery housing box. Also, one electrode is electrically connected to the control circuit portion 1320 by a wiring 1421. Also, the other electrode is electrically connected to the control circuit portion 1320 by a wiring 1422.

[0456] Further, the control circuit portion 1320 may use a memory circuit including a transistor using an oxide semiconductor. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as BTOS (Battery operating system, or Battery oxide semiconductor).

[0457] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the metal oxide, it is advisable to use a metal oxide such as an In-M-Zn oxide (element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium, etc.). In particular, the In-M-Zn oxide that can be applied as the metal oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Also, as the metal oxide, In-Ga oxide or In-Zn oxide may be used. CAAC-OS is an oxide semiconductor having a plurality of crystal regions, and the c-axis of the plurality of crystal regions is oriented in a specific direction. Note that the specific direction is the thickness direction of the CAAC-OS film, the normal direction of the surface on which the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. Also, the crystal region is a region having periodicity in the atomic arrangement. Note that when the atomic arrangement is regarded as a lattice arrangement, the crystal region is also a region where the lattice arrangement is aligned.

[0458] Note that in "CAC-OS", the material separates into a first region and a second region to form a mosaic pattern, and the first region has a structure distributed in the film (hereinafter also referred to as a cloud-like structure). That is, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed. However, it may be difficult to observe a clear boundary between the first region and the second region.

[0459] For example, in the CAC-OS of In-Ga-Zn oxide, it can be confirmed by EDX mapping obtained using EDX that the region mainly composed of In (the first region) and the region mainly composed of Ga (the second region) are unevenly distributed and have a mixed structure.

[0460] When using CAC-OS in a transistor, the conductivity caused by the first region and the insulating property caused by the second region act complementarily, enabling the function of switching (turning on / off) to be imparted to the CAC-OS. That is, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and has a function as a semiconductor in the whole material. By separating the conductive function and the insulating function, both functions can be enhanced to the maximum extent. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), a high field-effect mobility (μ), and a good switching operation can be realized.

[0461] Oxide semiconductors have various structures and each has different characteristics. The oxide semiconductor of one aspect of the present invention may have two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0462] In addition, since it can be used in a high-temperature environment, it is preferable that the control circuit unit 1320 uses a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. The transistor using an oxide semiconductor for the semiconductor layer has an operating ambient temperature range wider than that of a single-crystalline Si transistor, from -40°C to 150°C or higher, and even when the secondary battery overheats, the characteristic change is smaller than that of a single crystal. The off-current of the transistor using an oxide semiconductor is less than the measurement lower limit regardless of temperature even at 150°C, while the off-current characteristic of a single-crystalline Si transistor has a large temperature dependence. For example, at 150°C, the off-current of a single-crystalline Si transistor increases and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety. In addition, by combining with the secondary battery using the positive electrode active material 100 described in Embodiment 1, 2, etc. for the positive electrode, a synergistic effect on safety can be obtained. The secondary battery using the positive electrode active material 100 described in Embodiment 1, 2, etc. for the positive electrode and the control circuit unit 1320 can greatly contribute to extinguishing accidents such as fires caused by the secondary battery.

[0463] The control circuit unit 1320 using a memory circuit including a transistor using an oxide semiconductor can also function as an automatic control device for a secondary battery against the causes of 10 items of instability such as micro-shorts. As functions for eliminating the causes of 10 items of instability, prevention of overcharge, prevention of overcurrent, overheat control during charging, cell balance in a battery pack, prevention of overdischarge, remaining amount meter, automatic control of charging voltage and current according to temperature, control of charging current according to degree of deterioration, detection of abnormal behavior of micro-short, prediction of abnormality related to micro-short, etc. are mentioned, and the control circuit unit 1320 has at least one of these functions. Also, miniaturization of the automatic control device for a secondary battery is possible.

[0464] Also, "micro-short" refers to a minute short circuit inside the secondary battery, not to the extent that the positive and negative electrodes of the secondary battery are short-circuited and charging and discharging become impossible, but to the phenomenon that a slight short-circuit current flows through a minute short-circuit part. Since a large voltage change occurs even in a relatively short time and at a small location, there is a risk that the abnormal voltage value will affect subsequent estimation.

[0465] One of the causes of micro-short is said to be that due to repeated charging and discharging, non-uniform distribution of the positive electrode active material causes local current concentration between a part of the positive electrode and a part of the negative electrode, resulting in a part of the separator becoming non-functional, or a micro short circuit occurring due to the generation of side reaction products due to side reactions.

[0466] Also, not only detection of micro-short, but the control circuit unit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge and discharge state of the secondary battery. For example, in order to prevent overcharge, both the output transistor of the charging circuit and the cutoff switch can be turned off almost simultaneously.

[0467] Next, an example of the block diagram of the battery pack 1415 shown in Fig. 19(A) is shown in Fig. 19(B).

[0468] The control circuit unit 1320 includes at least a switch for preventing overcharging, a switch unit 1324 including a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has the upper limit voltage and the lower limit voltage of the secondary battery to be used set, and limits the upper limit of the current from the outside or the upper limit of the output current to the outside. The range within the lower limit voltage and the upper limit voltage of the secondary battery is the voltage range in which use is recommended. When outside this range, the switch unit 1324 operates and functions as a protection circuit. Further, since the control circuit unit 1320 controls the switch unit 1324 to prevent overdischarging and / or overcharging, it can also be called a protection circuit. For example, when the control circuit 1322 detects a voltage that is likely to cause overcharging, the switch of the switch unit 1324 is turned off to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function of cutting off the current in response to an increase in temperature. The control circuit unit 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0469] The switch section 1324 can be configured by combining an n-channel transistor or a p-channel transistor. The switch section 1324 is not limited to a switch having an Si transistor using single-crystalline silicon. For example, the switch section 1324 may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaOx (gallium oxide; x is a real number greater than 0), or the like. In addition, since a memory element using an OS transistor can be freely arranged by laminating it on a circuit using an Si transistor or the like, integration can be easily performed. Further, since an OS transistor can be manufactured using the same manufacturing apparatus as an Si transistor, it can be manufactured at low cost. That is, a control circuit section 1320 using an OS transistor can be laminated on the switch section 1324 and integrated into one chip. Since the occupied volume of the control circuit section 1320 can be reduced, miniaturization is possible.

[0470] The first batteries 1301a and 1301b mainly supply power to in-vehicle devices of a 42V system (high-voltage system HV), and the second battery 1311 supplies power to in-vehicle devices of a 14V system (low-voltage system LV). The second battery 1311 is often adopted because a lead-acid battery is advantageous in terms of cost. A lead-acid battery has a disadvantage in that self-discharge is large compared to a lithium-ion battery and it is easily deteriorated by a phenomenon called sulfation. Although there is an advantage of making the second battery 1311 maintenance-free by using a lithium-ion battery, when used for a long period, for example, for three years or more, there is a possibility that an abnormality that is difficult to discriminate at the time of manufacture may occur. In particular, when the second battery 1311 that starts the inverter becomes inoperable, in order to prevent the motor from being unable to start even if the first batteries 1301a and 1301b have remaining capacity, when the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery and it is charged so as to always maintain a fully charged state.

[0471] In this embodiment, an example is shown in which lithium-ion batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may use a lead-acid battery, a solid-state battery, or an electric double-layer capacitor.

[0472] Also, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and is charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or the battery controller 1302. Or it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Or it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0473] The battery controller 1302 can set the charging voltage, charging current, etc. of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery to be used and perform rapid charging.

[0474] Also, although not shown in the figure, when connecting an electric vehicle to an external charger, the charger plug or the charger connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is used to charge the first batteries 1301a and 1301b via the battery controller 1302. Also, depending on the charger, a control circuit may be provided and, in some cases where the functions of the battery controller 1302 are not used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. Also, in some cases, the charger plug or the charger connection cable may be equipped with a control circuit. The control circuit unit 1320 may also be referred to as an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. Also, the ECU includes a microcomputer. Also, the ECU uses a CPU or a GPU.

[0475] External chargers installed in charging stations, etc. include 100V outlets - 200V outlets, or three-phase 200V and 50kW, etc. Also, it is possible to receive power supply from external charging facilities by a non-contact power supply method, etc., and charge the vehicle.

[0476] When performing rapid charging, in order to charge in a short time, a secondary battery that can withstand charging at a high voltage is desired.

[0477] Also, by using graphene as a conductive material and increasing the thickness of the electrode layer and the loading amount to suppress capacity degradation and maintain a high capacity, a secondary battery with significantly improved electrical characteristics can be realized as a synergistic effect. It is particularly effective for secondary batteries used in vehicles, and it is possible to provide a vehicle with a long cruising range, specifically, a vehicle with a single-charge driving range of 500 km or more, without increasing the ratio of the weight of the secondary battery to the total vehicle weight.

[0478] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the positive electrode active material 100 described in Embodiments 1, 2, etc., and can increase the usable capacity as the charging voltage increases. Further, by using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0479] Next, an example of mounting the secondary battery, which is one aspect of the present invention, on a vehicle, typically a transportation vehicle, will be described.

[0480] When the secondary battery shown in any one of FIGS. 13(D), 15(C), and 19(A) is mounted on a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Further, the secondary battery can also be mounted on agricultural machinery, motorized bicycles including electric assist bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, airplanes, rockets, artificial satellites, space exploration vehicles, planetary exploration vehicles, or spacecraft. The secondary battery of one aspect of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one aspect of the present invention is suitable for miniaturization and weight reduction, and can be preferably used for transportation vehicles.

[0481] In FIGS. 20(A) to (D), a transportation vehicle using one aspect of the present invention is illustrated. The automobile 2001 shown in FIG. 20(A) 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. When mounting the secondary battery on a vehicle, an example of the secondary battery shown in Embodiment 4 is installed at one location or at a plurality of locations. The automobile 2001 shown in FIG. 20(A) has a battery pack 2200, and the battery pack has a secondary battery module in which a plurality of secondary batteries are connected. Further, it is preferable to have a charge control device electrically connected to the secondary battery module.

[0482] In addition, the motor vehicle 2001 can be charged by receiving power supply from an external charging facility by means of a plug-in method or a non-contact power supply method or the like to a secondary battery included in the motor vehicle 2001. When charging, the charging method, the standard of the connector, etc. may be appropriately carried out in a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging facility may be a charging station provided in a commercial facility or may be a household power source. For example, by means of a plug-in technique, the power storage device mounted on the motor vehicle 2001 can be charged by external power supply. Charging can be performed by converting AC power into DC power via a conversion device such as an AC-DC converter.

[0483] Also, although not shown, a power receiving device can be mounted on the vehicle and power can be supplied non-contact from a power transmitting device on the ground for charging. In the case of this non-contact power supply method, by incorporating a power transmitting device in a road or an outer wall, charging can be performed not only while the vehicle is stopped but also while it is running. Further, power transmission and reception can be performed between two vehicles using this non-contact power supply method. Furthermore, a solar cell may be provided on the exterior portion 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.

[0484] FIG. 20(B) shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has, for example, four secondary batteries with a nominal voltage of 3.0 V or more and 5.0 V or less as a cell unit, and a maximum voltage of 170 V with 48 cells connected in series. Since it has the same functions as FIG. 20(A) except for the number of secondary batteries constituting the secondary battery module of the battery pack 2201 being different, the description thereof is omitted.

[0485] Figure 20(C) shows, as an example, a large transport vehicle 2003 having a motor controlled electrically. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, for example, by connecting more than a hundred secondary batteries with a nominal voltage of 3.0V or more and 5.0V or less in series. Therefore, a secondary battery with small characteristic variations is required. By using the secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode, a secondary battery having stable battery characteristics can be manufactured, and mass production can be achieved at low cost from the viewpoint of yield. Also, since it has the same functions as in Fig. 23(A) except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the description thereof is omitted.

[0486] Figure 20(D) shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 20(D) has wheels for takeoff and landing, it can be said to be a kind of transport vehicle, and has a battery pack 2203 including a secondary battery module configured by connecting a plurality of secondary batteries and a charge control device.

[0487] The secondary battery module of the aircraft 2004 has a maximum voltage of 32V by connecting 8 secondary batteries of 4V in series, for example. Since it has the same functions as in Fig. 20(A) except for the number of secondary batteries constituting the secondary battery module of the battery pack 2203, the description thereof is omitted.

[0488] Figure 20(E) shows, as an example, a satellite 2005 equipped with a secondary battery 2204. Inside the satellite 2005, it is preferable that the secondary battery 2204 is mounted in a state covered with a heat insulating member.

[0489] The content of this embodiment can be freely combined with the content of other embodiments.

[0490] (Embodiment 6) In this embodiment, an example of mounting a secondary battery, which is an aspect of the present invention, on a building will be described with reference to Figs. 21(A) and 21(B).

[0491] The house shown in Fig. 21(A) has a power storage device 2612 having a secondary battery which is one aspect of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611 and the like. Also, the power storage device 2612 and a ground-mounted charging device 2604 may be electrically connected. The electric power obtained by the solar panel 2610 can be used to charge the power storage device 2612. Also, the electric power stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space on the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0492] The electric power stored in the power storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the power storage device 2612 according to one aspect of the present invention as an uninterruptible power supply, the use of electronic devices becomes possible.

[0493] Fig. 21(B) shows an example of a power storage device according to one aspect of the present invention. As shown in Fig. 21(B), a power storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Also, by using the secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode in the power storage device 791, a synergistic effect regarding safety can be obtained. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode can greatly contribute to extinguishing an accident such as a fire by the power storage device 791 having the secondary battery.

[0494] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to the distribution board 703, the power storage controller 705 (also referred to as a control device), the display 706, and the router 709 by wiring.

[0495] Electric power is sent from the commercial power supply 701 to the distribution board 703 via the lead wire attachment part 710. Also, electric power is sent to the distribution board 703 from the power storage device 791 and the commercial power supply 701, and the distribution board 703 supplies the received electric power to the general load 707 and the power storage system load 708 via an outlet (not shown).

[0496] The general load 707 is an electronic device such as a TV or a personal computer, and the power storage system load 708 is an electronic device such as a microwave oven, a refrigerator, or an air conditioner.

[0497] The power storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of electric power consumed by the general load 707 and the power storage system load 708 during one day (for example, from 0:00 to 24:00). Also, the measurement unit 711 may have a function of measuring the amount of electric power of the power storage device 791 and the amount of electric power supplied from the commercial power supply 701. Further, the prediction unit 712 has a function of predicting the required amount of electric power to be consumed by the general load 707 and the power storage system load 708 during the next day based on the amount of electric power consumed by the general load 707 and the power storage system load 708 during one day. Moreover, the planning unit 713 has a function of making a charge / discharge plan for the power storage device 791 based on the required amount of electric power predicted by the prediction unit 712.

[0498] The amount of electric power consumed by the general load 707 and the power storage system load 708 measured by the measurement unit 711 can be confirmed by the display 706. Also, it can be confirmed on an electronic device such as a TV or a personal computer via the router 709. Furthermore, it can also be confirmed by a portable electronic terminal such as a smartphone or a tablet via the router 709. Also, the required amount of electric power for each time period (or for each hour) predicted by the prediction unit 712 can be confirmed by the display 706, the electronic device, and the portable electronic terminal.

[0499] The content of this embodiment can be freely combined with the content of other embodiments.

[0500] (Embodiment 7) In this embodiment, as an example of mounting a secondary battery on a vehicle, an example of mounting a lithium-ion battery, which is one aspect of the present invention, on a two-wheeler or a bicycle is shown.

[0501] FIG. 22(A) is an example of an electric bicycle using a power storage device according to one aspect of the present invention. The power storage device according to one aspect of the present invention can be applied to the electric bicycle 8700 shown in FIG. 22(A). The power storage device according to one aspect of the present invention has, for example, a plurality of storage batteries and a protection circuit.

[0502] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the driver. Further, the power storage device 8702 can be carried and is shown in a state of being removed from the bicycle in FIG. 22(B). Further, the power storage device 8702 incorporates a plurality of storage batteries 8701 included in the power storage device according to one aspect of the present invention, and can display the remaining battery level and the like on a display unit 8703. Further, the power storage device 8702 has a control circuit 8704 capable of controlling charging of the secondary battery or detecting an abnormality. The control circuit 8704 is electrically connected to the positive electrode and the negative electrode of the storage battery 8701. Further, by combining with the secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode, a synergistic effect on safety can be obtained. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode and the control circuit 8704 can greatly contribute to extinguishing an accident such as a fire caused by the secondary battery.

[0503] FIG. 22(C) is an example of a two-wheeler using a power storage device according to one aspect of the present invention. The scooter 8600 shown in FIG. 22(C) includes a power storage device 8602, a side mirror 8601, and a direction indicator light 8603. The power storage device 8602 can supply electricity to the direction indicator light 8603. Further, the power storage device 8602 in which a plurality of secondary batteries using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode are stored can have a high capacity and can contribute to miniaturization.

[0504] In addition, in the scooter 8600 shown in FIG. 22(C), the power storage device 8602 can be stored in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the power storage device 8602 can be stored in the under-seat storage 8604.

[0505] The content of this embodiment can be freely combined with the content of other embodiments.

[0506] (Embodiment 8) 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. Examples of the electronic device on which the secondary battery is mounted include, for example, a television device (also referred to as a TV or a 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 a mobile phone device), a portable game machine, a portable information terminal, an audio reproduction device, and a large game machine such as a pachinko machine. Examples of the portable information terminal include a notebook personal computer, a tablet terminal, an e-book terminal, and a mobile phone.

[0507] FIG. 23(A) shows an example of a mobile phone. The mobile phone 2100 includes, in addition to a display unit 2102 incorporated in a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 has a secondary battery 2107. By providing the secondary battery 2107 using the positive electrode active material 100 described in Embodiments 1, 2, etc. as the positive electrode, a high capacity can be achieved, and a configuration that can cope with space saving accompanying the miniaturization of the housing can be realized.

[0508] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mails, text viewing and creation, music reproduction, Internet communication, and computer games.

[0509] In addition to time setting, the operation button 2103 can have 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 2103 can also be freely set by the operating system incorporated in the mobile phone 2100.

[0510] In addition, the mobile phone 2100 can execute communication-standardized short-range wireless communication. For example, it can also make hands-free calls by communicating with a wireless headset.

[0511] The mobile phone 2100 is also provided with an external connection port 2104 and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that the charging operation may also be performed by wireless power supply without using the external connection port 2104.

[0512] The mobile phone 2100 preferably has a sensor. As the sensor, for example, it is preferable to mount a human body sensor such as a fingerprint sensor, a pulse sensor, or a body temperature sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0513] FIG. 23(B) shows a drone 2300 having a plurality of rotors 2302. The drone 2300 is also sometimes called an unmanned aerial vehicle. The drone 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are aspects of the present invention. The drone 2300 can be remotely operated via the antenna. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. has a high energy density and high safety, so it can be safely used for a long time over a long period and is suitable as the secondary battery mounted on the drone 2300.

[0514] FIG. 23(C) shows an example of a robot. The robot 6400 shown in FIG. 23(C) includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, an arithmetic unit, etc.

[0515] The microphone 6402 has a function of detecting the user's voice, ambient sound, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0516] The display unit 6405 has a function of displaying various information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer are made possible.

[0517] The upper camera 6403 and the lower camera 6406 have a function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0518] The robot 6400 includes a secondary battery 6409 according to an aspect of the present invention and a semiconductor device or electronic components in its internal area. The secondary battery using the positive electrode active material 100 described in Embodiment 1, 2, etc. for the positive electrode has a high energy density and high safety, so it can be used safely for a long time over a long period, and is suitable as the secondary battery 6409 mounted on the robot 6400.

[0519] FIG. 23(D) shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the upper surface of the housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, operation buttons 6305, a secondary battery 6306, various sensors, etc. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, etc. The cleaning robot 6300 can move automatically, detect dust 6310, and suck the dust from the suction port provided on the lower surface.

[0520] The cleaning robot 6300 can analyze the image captured by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Also, when an object that is likely to get caught in the brush 6304, such as wiring, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to an aspect of the present invention and a semiconductor device or electronic components in its internal area. The secondary battery using the positive electrode active material 100 described in Embodiment 1, 2, etc. has a high energy density and high safety, so it can be safely used for a long time over a long period, and is suitable as the secondary battery 6306 mounted on the cleaning robot 6300.

[0521] FIG. 24(A) shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Also, when the user uses it in daily life or outdoors, a wearable device that can perform not only wired charging with the connector part exposed to enhance the anti-foaming performance, water resistance performance, or dustproof performance, but also wireless charging is desired.

[0522] For example, a secondary battery according to an aspect of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 24(A). The glasses-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery on the temple part of the frame 4000a having a curvature, it is possible to obtain a glasses-type device 4000 that is lightweight, has a good weight balance, and has a long continuous use time. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0523] Further, a secondary battery according to an aspect of the present invention can be mounted on a headset-type device 4001. The headset-type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided inside the flexible pipe 4001b or inside the earphone unit 4001c. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0524] Further, a secondary battery according to an aspect of the present invention can be mounted on a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0525] Further, a secondary battery according to an aspect of the present invention can be mounted on a device 4003 that can be attached to clothing. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0526] In addition, a secondary battery according to one aspect of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power feeding / receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode has a high energy density and can realize a configuration that can cope with space saving accompanying the miniaturization of the housing.

[0527] In addition, a secondary battery according to one aspect of the present invention can be mounted on the wristwatch-type device 4005. The wristwatch-type device 4005 has a display portion 4005a and a belt portion 4005b, and a secondary battery can be provided in the display portion 4005a or the belt portion 4005b. The secondary battery using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode has a high energy density and can realize a configuration that can cope with space saving accompanying the miniaturization of the housing.

[0528] The display portion 4005a can display various information such as not only the time but also incoming mails or calls.

[0529] In addition, since the wristwatch-type device 4005 is a wearable device of a type that is directly wound around the wrist, a sensor for measuring the user's pulse, blood pressure, etc. may be mounted. Data regarding the user's exercise amount and health can be accumulated to manage the health.

[0530] Fig. 24(B) shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0531] In addition, a side view is shown in Fig. 24(C). Fig. 24(C) shows a state in which the secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery shown in Embodiment 4. The secondary battery 913 is provided at a position overlapping the display portion 4005a, and can be made high density and high capacity, and is small and lightweight.

[0532] In the wristwatch-type device 4005, since it is required to be small and lightweight, by using the positive electrode active material 100 described in Embodiments 1, 2, etc. for the positive electrode of the secondary battery 913, a secondary battery 913 with a high energy density and small size can be obtained.

[0533] The content of this embodiment can be freely combined with the content of other embodiments.

Example

[0534] In this example, magnesium, nickel, and aluminum were added to lithium cobaltate that had undergone initial heating to prepare a positive electrode active material with reference to Embodiment 1, and its properties were evaluated.

[0535] <Fabrication of positive electrode active material> With reference to the fabrication method shown in FIGS. 2 to 3(B), the fabrication of the positive electrode active material in this example will be described.

[0536] <Sample 2> As the LiCoO2 (starting material) in step S10 of FIG. 2, commercially available lithium cobaltate (manufactured by Nippon Chemical Industry Co., Ltd., Celsid C-10N) having cobalt as the transition metal M and no particular additive element was prepared. As the second lithium source (Li source 2) in step S15, lithium fluoride was prepared. In step S16, after mixing the above lithium cobaltate and lithium fluoride, as the initial heating in step S17, the above mixture was placed in a crucible, covered, and heated in a muffle furnace at 850 ° C. for 2 hours. The inside of the muffle furnace was made into an oxygen atmosphere and then not flowed (O2 purge). In the mixing in step S16, when the number of moles of lithium cobaltate was 100, lithium fluoride was weighed and mixed so that the number of moles became 0.33 (0.33 mol%). A ball mill was used for mixing, and zirconium oxide balls were used as the grinding media.

[0537] According to steps S21 to S23 shown in FIG. 3(A) and steps S41 to S43 shown in FIG. 3(B), Mg, F, Ni, and Al were added separately as additive elements.

[0538] According to step S21 shown in FIG. 3(A), lithium fluoride (LiF) was prepared as the F source, and magnesium fluoride (MgF2) was prepared as the Mg source. LiF:MgF2 was weighed so as to be 1:3 (molar ratio). Next, lithium fluoride and magnesium fluoride were mixed in dehydrated acetone and stirred at a rotation speed of 400 rpm for 12 hours to prepare an additive element source (A1 source). A ball mill was used for mixing, and zirconium oxide balls were used as the grinding media. After mixing, sieving was performed with a sieve having a mesh size of 300 μm to obtain the A1 source.

[0539] Next, as step S31, when the number of moles of lithium cobaltate was set to 100, magnesium fluoride contained in the A1 source was weighed so as to be 1 (1 mol%) and dry-mixed with lithium cobaltate after initial heating. At this time, stirring was performed at a rotation speed of 150 rpm for 1 hour. This is a gentler condition than the stirring when obtaining the A1 source. Finally, sieving was performed with a sieve having a mesh size of 300 μm to obtain a mixture 903 with uniform particle size (step S32).

[0540] Next, as step S33, the mixture 903 was heated. The heating conditions were 900 °C and 20 hours. During heating, a lid was placed on the crucible containing the mixture 903. The inside of the crucible was an atmosphere containing oxygen, and the entry and exit of the oxygen were blocked (purged). By heating, a composite oxide containing Mg and F was obtained (step S34a).

[0541] Next, as step S51, the composite oxide and the additive element source (A2 source) were mixed. According to step S41 shown in FIG. 3(B), nickel hydroxide was prepared as the Ni source, and aluminum hydroxide was prepared as the Al source. When the number of moles of lithium cobaltate was set to 100, nickel hydroxide contained in the A2 source was weighed so that the number of moles was 0.5 (0.5 mol%), and aluminum hydroxide was weighed so that the number of moles was 0.5 (0.5 mol%), and they were mixed with the composite oxide in a dry manner. At this time, stirring was performed at a rotation speed of 150 rpm for 1 hour. A ball mill was used for mixing, and zirconium oxide balls were used as the grinding media. After mixing, sieving was performed with a sieve having a mesh size of 300 μm to obtain a mixture 904 with uniform particle size (step S52).

[0542] Next, as step S53, the mixture 904 was heated. The heating conditions were 850 °C and 10 hours. During heating, a lid was placed on the crucible containing the mixture 904. The inside of the crucible was an atmosphere containing oxygen, and the entry and exit of the oxygen were blocked (purged). By heating, lithium cobaltate having Mg, F, Ni, and Al was obtained (step S54). The positive electrode active material (composite oxide) thus obtained was designated as Sample 2.

[0543] <Sample 1> In step S21, a sample prepared in the same manner as Sample 2 except that lithium fluoride (F source) was not prepared and the A1 source in step S23 was changed to only magnesium fluoride was designated as Sample 1.

[0544] <Sample 3> In step S17, a sample prepared in the same manner as Sample 1 except that the heating temperature was changed to 900 °C was designated as Sample 3.

[0545] <Sample 4> In step S17, a sample prepared in the same manner as Sample 2 except that the heating temperature was changed to 900 °C was designated as Sample 4.

[0546] <Sample 5> In step S15, without preparing lithium fluoride (Li source 2) and without performing step S16, that is, in step S17, a sample prepared in the same manner as sample 2 except that only lithium cobaltate as the starting material was heated was designated as sample 5.

[0547] <Sample 6> In step S15, without preparing lithium fluoride (Li source 2) and without performing step S16, that is, in step S17, a sample prepared in the same manner as sample 4 except that only lithium cobaltate as the starting material was heated was designated as sample 6.

[0548] The preparation conditions of the samples are shown in Table 1. The mol% shown in Table 1 is the ratio with respect to the number of moles of LiCoO2. Also, "none" in the table indicates that the initial heat treatment was performed without adding the second lithium source (Li source 2). That is, sample 5 and sample 6 are comparative examples in this example.

[0549]

Table 1

[0550] <Particle size distribution measurement> For samples 1 to 6, the particle size distribution was measured using a laser diffraction particle size distribution measuring device. As the measurement results of the particle size distribution, D50, D10, and D90 are shown in Table 2.

[0551]

Table 2

[0552] <HAADF-STEM analysis, EELS analysis> To investigate the influence of the initial heating in step S17, the materials during the processes of sample 4 and sample 5 were analyzed. As the analysis, HAADF-STEM analysis and EELS (electron energy-loss spectroscopy) analysis were performed using the starting material LiCoO2 (step S10), LiCoO2 that had undergone initial heating during the production of sample 4 (LiCoO2 after mixing lithium fluoride as the second lithium source and performing step S17), and LiCoO2 that had undergone initial heating during the production of sample 5 (LiCoO2 after performing step S17 without mixing the second lithium source).

[0553] HAADF-STEM analysis and EELS analysis were performed using the following equipment. ≪HAADF-STEM Analysis≫ Analysis method: High-angle annular dark-field method (HAADF) Scanning transmission electron microscope: JEM-ARM200F NEOARM manufactured by JEOL Accelerating voltage: 200 kV ≪EELS Analysis≫ Analysis method: Electron energy-loss spectroscopy (EELS) Scanning transmission electron microscope: JEM-ARM200F NEOARM manufactured by JEOL Accelerating voltage: 200 kV EELS detector: ContinuumK3 manufactured by Gatan Dwell Time: 0.5 sec Number of frames: 40

[0554] Fig. 25 shows the HAADF-STEM image of the starting material LiCoO2 (step S10). Fig. 26(A) shows the HAADF-STEM image of LiCoO2 that had undergone initial heating during the production of sample 4. Fig. 26(B) shows the HAADF-STEM image of LiCoO2 that had undergone initial heating during the production of sample 5.

[0555] In FIGS. 25, 26(A), and 26(B), EELS analysis was performed at each of the points labeled A to L in the figures. The results of these EELS analyses are shown in Table 3. In the EELS analysis, the valence of cobalt was analyzed at analysis points (the above points A, B, C, E, F, G, I, J, and K) within 2 nm from the surface (the position where bright spots can be clearly seen) in the HAADF-STEM of each sample. As the analysis of the valence of cobalt, the valence of cobalt in the measurement data was calculated from a calibration curve of the relationship between the position of the maximum value of the pre-prepared cobalt L3 peak and the cobalt valence. For the creation of the above calibration curve, EELS analysis data in the bulk part (inside the particles) of lithium cobalt phosphate (LiCoPO4, cobalt valence 2.0), cobalt tetroxide (Co3O4, cobalt valence 2.7), and lithium cobalt oxide (LiCoO2, cobalt valence 3.0) were used. Also, assuming that only two types of crystal structures, a layered rock salt-type crystal structure (cobalt valence 3) and a rock salt-type crystal structure (cobalt valence 2), exist at the analysis points based on the above valence of cobalt, the ratio was calculated, and the ratio of the rock salt-type crystal structure (rock salt ratio) and the ratio of the layered rock salt-type crystal structure (layered rock salt ratio) calculated are shown in Table 3.

[0556]

Table 3

[0557] As a result of the EELS analysis, it became clear that LiCoO2 that had undergone initial heating during the production of Sample 4 had a relatively high valence of cobalt near the surface of the surface layer of the particles, that is, the ratio of the rock salt-type crystal structure was small. In other words, it became clear that LiCoO2 that had undergone initial heating during the production of Sample 4 had a high ratio of the layered rock salt-type crystal structure near the surface of the surface layer of the particles.

[0558] <STEM-EDX Analysis> Cross-sectional STEM-EDX analysis was performed in the edge region of the surface layer of Sample 4 and Sample 5.

[0559] As a pretreatment before subjecting to analysis, Sample 4 and Sample 5 were each thinned by the FIB method (μ-sampling method).

[0560] STEM and EDX were performed using the following apparatuses and conditions. ≪STEM Observation≫ Scanning transmission electron microscope: HF5000 manufactured by Hitachi High-Tech Observation conditions Acceleration voltage: 200 kV Magnification accuracy: ±3% ≪STEM-EDX Analysis≫ Analysis method: Energy-dispersive X-ray spectroscopy (EDX) Scanning transmission electron microscope: HF5000 manufactured by Hitachi High-Tech Acceleration voltage: 200 kV Observation mode: HR mapping mode was used Elemental analyzer: Equipped with UltimMaxTLE 2 apparatus X-ray detector: Si drift detector Energy resolution: Approximately 127 eV X-ray extraction angle: 23.9° Solid angle: 2.02 sr Number of pixels captured: 256×256

[0561] The results of cross-sectional STEM-EDX analysis of Sample 4 are shown in FIGS. 27(A) to 30(B). Also, the results of cross-sectional STEM-EDX analysis of Sample 5 are shown in FIGS. 31(A) to 34(B). Note that the above cross-sectional STEM-EDX analysis is a line analysis in the depth direction from the outside to the inside of the sample.

[0562] FIG. 27(A) is a graph showing the results of cross-sectional STEM-EDX analysis in the edge region of the surface layer part of Sample 4, with the vertical axis being the count value of characteristic X-rays, and FIG. 27(B) is a graph showing the vertical axis of the graph of FIG. 27(A) as a quantitative value of Atomic%. On the horizontal axis of FIGS. 27(A) and 27(B), the reference point on the particle surface is estimated to be at the position of 10 nm. Note that the position of the reference point was determined by the method described in Embodiment 2 (using the half-value of the count value of characteristic X-rays of oxygen).

[0563] Further, Fig. 28(A) is a graph with the vertical axis of Fig. 27(A) enlarged, and Fig. 28(B) is a graph with the vertical axis of Fig. 27(B) enlarged.

[0564] Also, the graph of magnesium (Mg K) in Fig. 28(A) is extracted and shown in Fig. 29(A), the graph of fluorine (F K) is extracted and shown in Fig. 29(B), the graph of nickel (Ni K) is extracted and shown in Fig. 29(C), and the graph of aluminum (Al K) is extracted and shown in Fig. 29(D).

[0565] Also, the graph of magnesium (Mg At%) in Fig. 28(B) is extracted and shown in Fig. 30(A), the graph of fluorine (F At%) is extracted and shown in Fig. 30(B), the graph of nickel (Ni At%) is extracted and shown in Fig. 30(C), an...

Claims

1. A battery having a positive electrode, The positive electrode comprises lithium cobalt oxide; The lithium cobalt oxide contains magnesium, aluminum, and nickel, In an XPS analysis of the lithium cobalt oxide, when the concentration of cobalt is set to 1, the concentration of magnesium (Mg / Co) is 0.50 or more and 0.90 or less; In the XPS analysis, the half width of the Mg1s peak is 1.0 eV or more and 2.6 eV or less. battery.

2. In claim 1, When the magnesium concentration in the XPS analysis is taken as 1, the fluorine concentration (F / Mg) is 0.10 or more and 0.20 or less. battery.

3. In claim 2, When the concentration of cobalt in the XPS analysis is taken as 1, the concentration of aluminum (Al / Co) is 0.01 or more and 0.04 or less, and the concentration of nickel (Ni / Co) is 0.01 or more and 0.07 or less. battery.

4. In any one of claims 1 to 3, The lithium cobalt oxide has a layered rock-salt crystal structure of space group R-3m, The lithium cobalt oxide is used as a positive electrode, lithium metal is used as a negative electrode, and a mixture of lithium hexafluorophosphate, ethylene carbonate, diethyl carbonate, and 2 wt % vinylene carbonate is used as an electrolyte. In a 45° C. environment, the battery was charged at a constant current of 0.5 C (where 1 C=200 mA / g) up to a voltage of 4.60 V, and then charged at a constant voltage of 0.05 C. When the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation in an argon atmosphere, the XRD pattern has diffraction peaks at least at 2θ = 19.25 ± 0.12 ° and 2θ = 45.47 ± 0.10 °. battery.

5. A first step of mixing lithium cobalt oxide and lithium fluoride to prepare a first mixture; a second step of heating the first mixture at a temperature of 900° C. to 950° C. for a time period of 2 hours to 10 hours; a third step of mixing the first mixture with a magnesium source to form a second mixture; a fourth step of heating the second mixture at a temperature of 850° C. to 950° C. for a time period of 2 hours to 60 hours; a fifth step of mixing the second mixture with a nickel source and an aluminum source to form a third mixture; and a sixth step of heating the third mixture at a temperature of 800° C. or more and 900° C. or less for a time period of 2 hours or more and 20 hours or less.

6. In claim 5, wherein, when EELS analysis is performed on a portion within 2 nm from the surface of the first mixture that has been subjected to the second step, the valence of cobalt is 2.35 or more and 2.90 or less.

7. In claim 5, In the third step, the lithium fluoride is mixed in addition to the magnesium source.

8. In any one of claims 5 to 7, In the third step, magnesium fluoride is used as the magnesium source, the number of moles of the magnesium fluoride is 0.5 or more and 3.0 or less when the number of moles of the lithium cobalt oxide is taken as 100.

9. In claim 8, The method for producing a positive electrode active material, wherein in the fifth step, nickel hydroxide is used as the nickel source and aluminum hydroxide is used as the aluminum source.

10. In claim 9, the number of moles of the nickel hydroxide is 0.05 or more and 4.0 or less, and the number of moles of the aluminum hydroxide is 0.05 or more and 4.0 or less, when the number of moles of the lithium cobalt oxide is 100.

Images