Positive electrode active material and battery

Abstract

A positive electrode active material according to the present disclosure has an antifluorite crystal structure and contains: a lithium oxide into which nickel has been dissolved; and a metal oxide containing nickel. In an X-ray diffraction pattern measured using Cu-Kα rays, a diffraction peak derived from the metal oxide containing nickel is present in a diffraction angle 2θ range of 40° to 50°, and the ratio of the integrated intensity of a second diffraction peak belonging to the (220) plane of the lithium oxide and present within a diffraction angle 2θ range of 52° to 62° to the integrated intensity of a first diffraction peak belonging to the (111) plane of the lithium oxide and present within a diffraction angle 2θ range of 30° to 40° is greater than or equal to 0.48.

Description

Positive electrode active material and battery

[0001] The present disclosure relates to a positive electrode active material and a battery.

[0002] It has long been known that the redox reaction between lithium oxide (LiO) and lithium peroxide (LiO) can be applied to secondary batteries, as described in Patent Document 1. However, one of the technical challenges has been the poor electronic conductivity of lithium oxide and lithium peroxide, and the large overvoltage.

[0003] Patent Documents 2 and 3 disclose that charging overvoltage can be reduced by dissolving a transition metal in the crystal structure of lithium oxide.

[0004] Patent No. 4554935 Patent No. 6179944 Patent No. 6230149

[0005] The prior art has room for improvement in terms of discharge capacity.

[0006] The present disclosure provides a positive electrode active material comprising: lithium oxide having an inverse fluorite crystal structure and containing nickel as a solid solution; and a metal oxide containing nickel, wherein in an X-ray diffraction pattern measured using Cu-Kα radiation, a diffraction peak attributable to the metal oxide containing nickel is present in a diffraction angle 2θ range of 40° to 50°, and the ratio of the integrated intensity of a second diffraction peak attributable to a (220) plane of the lithium oxide, which exists in the diffraction angle 2θ range of 52° to 62°, to the integrated intensity of a first diffraction peak attributable to a (111) plane of the lithium oxide, which exists in the diffraction angle 2θ range of 30° to 40°, is 0.48 or more.

[0007] The positive electrode active material of the present disclosure can improve the discharge capacity.

[0008] FIG. 1 is a cross-sectional view showing a schematic configuration of a battery according to Embodiment 2. FIG. 2 shows X-ray diffraction patterns of the positive electrode active materials of Example 1 and Comparative Example 2. FIG. 3 shows an SEM image of the positive electrode active material of Example 4. FIG. 4 is a graph showing charge / discharge curves of Example 4 and Comparative Example 1. FIG. 5 is a graph plotting the calculation results of the integrated intensity ratio I2 / I1 and the integrated intensity ratio I3 / I1 of the positive electrode active materials of Example 1 and Comparative Example 1. FIG. 6A is an XAFS spectrum of the positive electrode active material of Example 1. FIG. 6B is a XANES spectrum of the positive electrode active material of Example 1. FIG. 6C is a graph showing the valence of nickel calculated from the XANES spectrum of FIG. 6B. FIG. 7A is an XAFS spectrum of the positive electrode active material of Example 4. FIG. 7B is a XANES spectrum of the positive electrode active material of Example 4. FIG. 7C is a graph showing the valence of nickel calculated from the XANES spectrum of FIG. 7B. FIG. 8 is a diagram showing the process of calculating the valence of nickel from the position of the absorption edge of the XANES spectrum.

[0009] (Findings that Form the Basis of the Present Disclosure) As described in Patent Document 2, mechanochemical treatment can be used to dissolve (do) transition metal atoms into the crystalline structure of lithium oxide. In mechanochemical treatment, for example, lithium oxide and α-iron oxide are mixed in a planetary ball mill. According to Patent Document 2, in some cases the iron is almost completely dissolved (Example 1), while in other cases the iron is only partially dissolved (Example 2). In the latter case, the product contains lithium oxide with dissolved iron and LiFeO2.

[0010] Patent Document 3 (Preparation Example 9) discloses that the solid powder obtained by mixing lithium oxide and nickel oxide (NiO) in a planetary ball mill is a mixture of LiO and NiO. A battery (Example 5) using this mixture in the positive electrode was chargeable, but the discharge capacity (Figure 11) was very low.

[0011] Based on the above findings, the present inventors have conducted extensive research and have completed the positive electrode active material of the present disclosure.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0013] (Embodiment 1) A positive electrode active material according to embodiment 1 includes lithium oxide with nickel dissolved therein and a metal oxide containing nickel. The lithium oxide with nickel dissolved therein has an inverse fluorite crystal structure. The inverse fluorite crystal structure is a structure in which the positional relationship between cations and anions in the fluorite structure is reversed. The reason why the electronic conductivity of lithium oxide with nickel dissolved therein is improved is not entirely clear, but it can be considered as follows. When nickel is dissolved in lithium oxide, nickel occupies the lithium site, and oxygen atoms are tetrahedral coordinated around the nickel, forming an outer orbital complex. As a result, multiple unpaired electrons are present in the 3d orbital, and these unpaired electrons impart electronic conductivity to the lithium oxide. Furthermore, assuming that the valence of nickel is +2, the valence of lithium is +1. Therefore, to maintain charge neutrality within the crystal, one lithium atom is released from the crystal in addition to the lithium atom substituted for nickel, forming a vacancy. This vacancy serves as a conduction path for lithium ions, improving the ionic conductivity of the lithium oxide. The lithium oxide containing nickel as a solid solution may be a substitutional solid solution.

[0014] The nickel-containing metal oxide has a composition different from that of lithium oxide in which nickel is dissolved. The nickel-containing metal oxide may include a metal oxide containing only nickel as a metallic element. The nickel-containing metal oxide may not contain lithium. The nickel-containing metal oxide may include a double oxide containing lithium and nickel. The nickel-containing metal oxide may include at least one selected from the group consisting of a double oxide containing lithium and nickel and a metal oxide containing only nickel as a metallic element. The nickel-containing metal oxide may typically be at least one selected from the group consisting of nickel oxide and lithium nickel oxide. Examples of nickel oxide include NiO(II). Examples of double oxides containing lithium and nickel include LiNiO2.

[0015] A metal oxide containing nickel may have the same crystal structure as or a different crystal structure from that of lithium oxide in which nickel is dissolved. For example, NiO(II) may have a crystal structure represented by the space group Fm-3m. The space group Fm-3m is the same as the space group of the inverse fluorite crystal structure. For example, LiNiO2 may have a crystal structure represented by the space group R-3m. NiO(II) may contain multiple types of crystals having different space groups. For example, NiO(II) may have not only a crystal structure represented by the space group Fm-3m, but also a crystal structure represented by the space group P6 / mmm.

[0016] In the X-ray diffraction pattern of the positive electrode active material measured using Cu-Kα radiation, a diffraction peak present in the range of a diffraction angle 2θ of 30° to 40° is defined as a first diffraction peak. A diffraction peak present in the range of a diffraction angle 2θ of 52° to 62° is defined as a second diffraction peak. The first diffraction peak is a diffraction peak attributable to the (111) plane of lithium oxide. The second diffraction peak is a diffraction peak attributable to the (220) plane of lithium oxide. The integrated intensity of the first diffraction peak is defined as I1, and the integrated intensity of the second diffraction peak is defined as I2. In this embodiment, the ratio of the integrated intensities I2 / I1 is 0.48 or more. By satisfying this condition, the positive electrode active material of this embodiment can improve the discharge capacity of a battery.

[0017] The integrated intensity ratio I2 / I1 is an index reflecting the degree of nickel solid solubility in lithium oxide crystals. Assuming that the valence of nickel is +2, the valence of lithium is +1. Therefore, in addition to the lithium atoms substituted for nickel to maintain charge neutrality within the crystal, one lithium atom is released from the crystal. Because nickel with a valence higher than that of lithium atoms is incorporated into the crystal and one lithium atom is released from the crystal to maintain charge neutrality, minute distortions occur in the crystalline structure of the lithium oxide base material. The greater the distortion, the greater the integrated intensity ratio I2 / I1. According to quantum science calculations, there is a proportional relationship between the amount of nickel doped into lithium oxide and the integrated intensity ratio I2 / I1. When the integrated intensity ratio I2 / I1 is below 0.48, the effect of improving electronic conductivity and ionic conductivity is insufficient due to insufficient nickel solid solubility, and therefore the effect of improving discharge capacity cannot be fully achieved.

[0018] When a nickel-containing metal oxide is present in an appropriate amount without being lost, the effect of improving discharge capacity is enhanced. The reason for this is not entirely clear, but the inventors speculate as follows: During the charging process, lithium atoms are removed from lithium oxide, oxygen ions are oxidized to peroxide ions, and lithium oxide is converted to lithium peroxide. Here, if the positive electrode active material is composed solely of lithium oxide in which nickel is completely dissolved, the volumetric shrinkage of the positive electrode active material during the charging process is significant, creating voids between the positive electrode active material and the conductive additive, increasing the electronic resistance of the entire electrode and causing an increase in charging voltage. In contrast, according to the present disclosure, the presence of a nickel-containing metal oxide in an appropriate amount in the positive electrode active material suppresses the volumetric shrinkage of the positive electrode active material during the charging process by utilizing charge compensation due to nickel valence change. As a result, the effect of suppressing the increase in charging voltage and the effect of improving discharge capacity are exhibited. Suppressing the increase in charging voltage also leads to suppressing the generation of oxygen gas. These effects are supported by the examples described below.

[0019] The lower limit of the integrated intensity ratio I / I may be 0.50 or 0.55. The upper limit of the integrated intensity ratio I / I is not particularly limited and may be 1.00 or 0.90. The integrated intensity ratio I / I may be 0.50 or more and 1.00 or less, 0.50 or more and 0.90 or less, 0.55 or more and 1.00 or less, or 0.55 or more and 0.90 or less.

[0020] The integrated intensity ratio I / I of a crystal of LiO that is not doped with nickel is approximately 0.33. When the integrated intensity ratio I / I exceeds 0.33 while maintaining the inverse fluorite crystal structure of LiO, it can be determined that nickel is dissolved in lithium oxide.

[0021] Diffraction peaks attributable to metal oxides containing nickel exist in the diffraction angle 2θ range of 40° to 50°. For example, the diffraction peak attributable to the (200) plane of NiO(II) exists in the diffraction angle 2θ range of 40° to 50°. Lithium oxide with nickel as a solid solution does not exhibit a peak in the diffraction angle 2θ range of 40° to 50°. In this respect, there is a difference between metal oxides containing nickel and lithium oxide with nickel as a solid solution.

[0022] The nickel-containing metal oxide is a residue and / or by-product of the raw material used to dissolve nickel in lithium oxide. In the X-ray diffraction pattern of the positive electrode active material measured using Cu-Kα radiation, a diffraction peak present in the diffraction angle 2θ range of 40° to 50° is defined as a third diffraction peak. The third diffraction peak is a diffraction peak attributable to a crystal plane of the nickel-containing metal oxide. The integrated intensity of the third diffraction peak is defined as I3. In this embodiment, the ratio of the integrated intensities I3 / I1 is 0.37 or more and 15.67 or less. By satisfying these conditions, the effect of improving the discharge capacity of the battery is enhanced.

[0023] The integrated intensity ratio I3 / I1 is an index reflecting the amount of nickel-containing metal oxide. For example, when nickel is dissolved in lithium oxide using NiO(II) or LiNiO2, at least one of NiO(II) and LiNiO2 is contained in the positive electrode active material as a residue and / or by-product. In this case, for example, reflection from the (200) plane of NiO(II) is observed as the third diffraction peak, and reflection from the (104) plane of LiNiO2 is observed as the third diffraction peak. As the amount of nickel-containing metal oxide decreases, the diffraction intensity of the third diffraction peak decreases, and therefore the integrated intensity ratio I3 / I1 also decreases. As the amount of nickel-containing metal oxide increases, the diffraction intensity of the third diffraction peak increases, and therefore the integrated intensity ratio I3 / I1 also increases. The composition and crystalline structure of the nickel-containing metal oxide can be determined from the entire X-ray diffraction pattern including the third diffraction peak. When crystals of a metal oxide containing nickel are present, a diffraction peak appears in the diffraction angle 2θ range of 40° to 50°.

[0024] The lower limit of the integrated intensity ratio I3 / I1 may be 0.53 or 0.67. The upper limit of the integrated intensity ratio I3 / I1 is not particularly limited and may be 3.95 or 1.50. The integrated intensity ratio I3 / I1 may be 0.53 or more and 1.50 or less, or 0.67 or more and 3.95 or less.

[0025] The lithium oxide containing nickel in a solid solution may have a composition represented by the following formulas (1a) and (1b) in a discharged state. According to quantum scientific calculations, when the valence of nickel is +3, α preferably satisfies the relationship 0.0327≦α≦0.1484. When the valence of nickel is +2, α preferably satisfies the relationship 0.0490≦α≦0.2224.

[0026] When the valence of nickel is +3: (Li (1-3α) Ni α ) 2O... (1a) When the valence of nickel is +2: (Li (1-2α) Ni α ) 2O... (1b)

[0027] The valence of nickel contained in the positive electrode active material may be 3.0 or less in a discharged state. As will be described later in the examples, when the valence of nickel in a discharged state is 3.0 or less, the valence of nickel changes significantly with charge and discharge. As a result, the positive electrode active material exhibits a large discharge capacity. The valence of nickel in a discharged state may be 2.0 or more and 3.0 or less. The valence of nickel can be calculated from a soft X-ray absorption fine structure (XANES) spectrum.

[0028] Here, the term "discharged state" refers not only to the state immediately after the preparation of the positive electrode active material, but also to the state in which the battery voltage is 2.0 V or less when simple lithium metal is used as the negative electrode active material.

[0029] The amount of lithium contained in the positive electrode active material is defined as m0 (mol). The amount of nickel contained in the positive electrode active material is defined as m1 (mol). The ratio (m1 / m0) is, for example, 0.058 to 0.350, preferably 0.080 to 0.333, more preferably 0.080 to 0.220, and even more preferably 0.088 to 0.167. By appropriately adjusting the ratio (m1 / m0), the effect of suppressing an increase in charging voltage and the effect of improving discharge capacity are enhanced.

[0030] The cathode active material of this embodiment has a secondary particle structure composed of multiple primary particles of lithium oxide and multiple primary particles of a metal oxide containing nickel. A cathode active material having such a structure can be efficiently produced by a synthesis method such as mechanochemical milling. The primary particles have diameters on the order of nanometers, for example. The secondary particles have diameters on the order of micrometers, for example.

[0031] The true density of the positive electrode active material is, for example, 2.2 g / cm 3 3.3g / cm or more 3 By appropriately adjusting the true density, the energy density of the battery can be improved compared to conventional lithium secondary batteries. The true density can be measured by the pycnometer method.

[0032] The specific surface area of ​​the positive electrode active material is, for example, 1.6 m2 / g or more 60m 2 / g or less, and 2 / g or more 20m 2 / g, and 2.0m 2 / g or more 10m 2 / g. By appropriately adjusting the specific surface area, the energy density of the battery can be improved. The specific surface area is a value determined by the BET method.

[0033] The positive electrode active material of this embodiment can be produced, for example, by a mechanochemical method. First, a mixture is prepared by mixing lithium oxide powder and a nickel raw material. The ratio of the lithium oxide to the nickel raw material can be determined so that the ratio (m1 / m0) described above falls within a desired range. Examples of nickel raw materials include nickel oxide, a composite oxide containing lithium and nickel, and elemental nickel.

[0034] When LiNiO2 is used as the nickel raw material, the valence of nickel in the discharged state is greater than 3. When NiO(II) is used as the nickel raw material, the valence of nickel in the discharged state can be suppressed to 3.0 or less.

[0035] The synthesis of the positive electrode active material by the mechanochemical method is carried out using a device capable of exerting a mechanochemical effect, such as a ball mill or a bead mill. The atmosphere during the synthesis is not particularly limited and may be an air atmosphere, an inert atmosphere, a dry atmosphere, or a dry inert atmosphere. In order to suppress the incorporation of inevitable impurities such as oxygen and water, it is desirable to synthesize the positive electrode active material in a dry inert atmosphere. For the inert atmosphere, for example, an inert gas such as nitrogen, argon, or helium is used.

[0036] The degree of nickel solid solubility in lithium oxide can be adjusted by adjusting conditions such as the rotation speed of the apparatus, processing time, processing temperature, raw material particle size, nickel raw material composition, and grinding media size. In other words, the integrated intensity ratio I / I can be controlled. For example, as the rotation speed and processing time increase, the solid solubility of nickel in lithium oxide progresses, and the ratio I / I increases. By setting the manufacturing conditions so that the integrated intensity ratio I / I falls within the desired range, a positive electrode active material can be obtained that can suppress an increase in charge voltage and improve discharge capacity.

[0037] The integrated intensity ratio I3 / I1 can also be controlled by adjusting the above conditions. For example, as the rotation speed and processing time increase, the solid solution of nickel into lithium oxide progresses, and the ratio I3 / I1 decreases. By setting the manufacturing conditions so that the integrated intensity ratio I3 / I1 falls within a desired range, the effect of suppressing an increase in charge voltage and the effect of improving discharge capacity are enhanced.

[0038] (Embodiment 2) FIG. 1 is a cross-sectional view of a battery 100 according to Embodiment 2. The battery 100 includes a positive electrode 23, a negative electrode 26, a non-aqueous electrolyte 29, a separator 27, and an exterior casing 28. The positive electrode 23 includes a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 is disposed on the positive electrode current collector 21. The negative electrode 26 includes a negative electrode current collector 24 and a negative electrode active material layer 25. The negative electrode active material layer 25 is disposed on the negative electrode current collector 24. A separator 27 is disposed between the positive electrode 23 and the negative electrode 26. The positive electrode 23 and the negative electrode 26 face each other with the separator 27 interposed therebetween. The positive electrode 23, the negative electrode 26, the separator 27, and the non-aqueous electrolyte 29 are housed in the exterior casing 28. The battery 100 is typically a secondary battery.

[0039] The positive electrode active material layer 22 contains the positive electrode active material described in embodiment 1. With this configuration, an increase in the charging voltage of the battery 100 is suppressed, and the discharge capacity of the battery 100 is improved.

[0040] The charge / discharge reaction in the battery 100 is as follows: Reaction at the positive electrode 23: Li2O2 + 2Li + +2e- ⇔2LiO Reaction at the negative electrode 26: Li ⇔ Li + +e -

[0041] The positive electrode current collector 21 is a sheet or film made of a metal material such as aluminum, an aluminum alloy, stainless steel, titanium, or a titanium alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may be applied to the surface of the positive electrode current collector 21 as a conductive auxiliary material.

[0042] The positive electrode active material layer 22 may contain other materials such as a conductive additive, an ion conductor, and a binder.

[0043] The conductive additive and the ion conductor are used to reduce the resistance of the positive electrode 23. Examples of the conductive additive include a carbon material and a conductive polymer compound. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive additives can be used.

[0044] Examples of ionic conductors include gel electrolytes such as polymethyl methacrylate and polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, and Li7La3Zr2O 12 At least one selected from these ion conductors can be used.

[0045] The binder is used to improve the binding properties of the materials constituting the negative electrode 26. Examples of binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one selected from these binders can be used.

[0046] The negative electrode current collector 24 is a sheet or film made of a metal material such as stainless steel, nickel, a nickel alloy, copper, or a copper alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may be applied to the surface of the negative electrode current collector 24 as a conductive auxiliary material.

[0047] The negative electrode active material layer 25 may contain a negative electrode active material capable of absorbing and desorbing lithium. Examples of negative electrode active materials capable of absorbing and desorbing lithium include lithium titanate, graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. At least one selected from these negative electrode active materials can be used. It is more preferable to use lithium metal as the negative electrode active material. The theoretical capacity of the positive electrode active material according to the present disclosure is 897 mAh per gram of lithium oxide, which is more than three times larger than other positive electrode active materials conventionally used. Therefore, lithium metal is suitable as the negative electrode active material.

[0048] The negative electrode active material layer 25 may contain other materials such as a conductive additive, an ion conductor, a binder, etc. Materials that can be used for the positive electrode active material layer 22 as the conductive additive, the ion conductor, and the binder can also be used for the negative electrode active material layer 25.

[0049] The non-aqueous electrolyte 29 may be impregnated into the positive electrode 23, the negative electrode 26, and the separator 27. The non-aqueous electrolyte 29 may fill the internal space of the exterior casing 28. The non-aqueous electrolyte 29 functions to allow lithium ions to travel between the positive electrode 23 and the negative electrode 26. The non-aqueous electrolyte 29 may include a non-aqueous electrolyte solution, a gel electrolyte, or an ionic liquid.

[0050] The non-aqueous electrolyte solution contains, for example, a non-aqueous solvent and a lithium salt.

[0051] Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, cyclic esters, chain esters, fluorine-containing solvents, and nitriles. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of chain ethers include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic esters include γ-butyrolactone. Examples of chain esters include methyl acetate. Examples of fluorine-containing solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethyl carbonate. Examples of nitriles include acetonitrile. At least one selected from these non-aqueous solvents can be used.

[0052] Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. At least one selected from these lithium salts can be used.

[0053] The gel electrolyte can be a material obtained by impregnating a polymer material with a non-aqueous electrolyte solution, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0054] Examples of cations constituting ionic liquids include aliphatic chain quaternary cations, aliphatic cyclic ammonium, and nitrogen-containing heterocyclic aromatic cations. Examples of aliphatic chain quaternary cations include tetraalkylammonium and tetraalkylphosphonium. Examples of aliphatic cyclic ammonium include pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, and piperidiniums. Examples of nitrogen-containing heterocyclic aromatic cations include pyridiniums and imidazoliums. Examples of anions constituting ionic liquids include PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2F)2 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , C(SO2CF3)3 - The ionic liquid may contain a lithium salt.

[0055] The separator 27 is an electrolyte layer having lithium ion conductivity. There are no particular limitations on the material of the separator 27 as long as it allows the passage of lithium ions. The material of the separator 27 can be at least one selected from the group consisting of solid electrolytes, gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 27 is made of these materials, the safety of the battery 100 can be sufficiently ensured. Examples of solid electrolytes include sulfide solid electrolytes such as Li2S-P2S5, Li7La3Zr2O 12Examples of the electrolyte include oxide solid electrolytes such as LLZ. Examples of the gel electrolyte include gel electrolytes containing fluororesins such as PVdF. Examples of the ion exchange resin membrane include cation exchange membranes and anion exchange membranes. Examples of the porous membrane include porous membranes made of polyolefin resins and porous membranes made of glass paper obtained by weaving glass fibers into nonwoven fabric.

[0056] The exterior 28 is made of a material obtained by laminating a metal foil such as an aluminum foil with a resin film such as a PET film, for example. The exterior 28 may also be a resin or metal container.

[0057] The shape of the battery 100 is not limited to the laminated type. Other shapes of the battery 100 include a coin type, a cylindrical type, a square type, a sheet type, a button type, and a flat type.

[0058] The battery 100 may be a solid-state battery.

[0059] When the battery 100 is a solid-state battery, a solid electrolyte is used in the positive electrode 23, the negative electrode 26, and the separator 27 instead of the nonaqueous electrolyte 29. Examples of the solid electrolyte include a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. At least one selected from these solid electrolytes can be used in each of the positive electrode 23, the negative electrode 26, and the separator 27.

[0060] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0061] (Technology 1) A positive electrode active material comprising: lithium oxide having an inverse fluorite crystal structure and containing nickel as a solid solution; and a metal oxide containing nickel, wherein in an X-ray diffraction pattern measured using Cu-Kα radiation, a diffraction peak attributable to the metal oxide containing nickel is present in a diffraction angle 2θ range of 40° to 50°, and the ratio of the integrated intensity of a second diffraction peak attributable to a (220) plane of the lithium oxide, which exists in the diffraction angle 2θ range of 52° to 62°, to the integrated intensity of a first diffraction peak attributable to a (111) plane of the lithium oxide, which exists in the diffraction angle 2θ range of 30° to 40°, is 0.48 or more.

[0062] The positive electrode active material of the present disclosure can suppress an increase in charging voltage and improve discharge capacity.

[0063] (Technology 2) The positive electrode active material according to Technology 1, wherein the ratio of the integrated intensity of a third diffraction peak attributable to a crystal plane of the nickel-containing metal oxide present in the diffraction angle 2θ range of 40° to 50° to the integrated intensity of the first diffraction peak is 0.37 or more and 15.67 or less. By satisfying such a condition, the effect of suppressing an increase in the charging voltage of the battery and the effect of improving the discharge capacity of the battery are enhanced.

[0064] (Technology 3) The positive electrode active material according to Technology 1 or 2, wherein the valence of nickel contained in the positive electrode active material is 3.0 or less in a discharged state. When the valence of nickel in a discharged state is 3.0 or less, the valence of nickel changes significantly with charge and discharge. As a result, the positive electrode active material exhibits a large discharge capacity.

[0065] (Technology 4) The cathode active material according to any one of Technologies 1 to 3, wherein the cathode active material has a secondary particle structure composed of a plurality of primary particles of the lithium oxide and a plurality of primary particles of the nickel-containing metal oxide. A cathode active material having such a structure can be efficiently produced by a synthesis method such as mechanochemical milling.

[0066] (Technology 5) The cathode active material according to any one of Technologies 1 to 4, wherein the ratio of the amount of nickel contained in the cathode active material to the amount of lithium contained in the cathode active material is 0.058 to 0.350. By appropriately adjusting this ratio, the effect of suppressing an increase in charging voltage and the effect of improving discharge capacity are enhanced.

[0067] (Technology 6) The true density of the positive electrode active material is 2.2 g / cm 3 3.3g / cm or more 3 6. A positive electrode active material according to any one of Techniques 1 to 5, which is as follows: By appropriately adjusting the true density, the energy density of the battery can be improved compared to conventional lithium secondary batteries.

[0068] (Technology 7) The specific surface area of ​​the positive electrode active material is 1.6 m 2 / g or more 60m 2 / g or less. By appropriately adjusting the specific surface area, the energy density of the battery can be improved.

[0069] (Technology 8) A battery comprising a positive electrode containing the positive electrode active material according to any one of Technologies 1 to 7. With this configuration, an increase in the charging voltage of the battery is suppressed, and the discharge capacity of the battery is improved.

[0070] Hereinafter, each operation in the preparation of the positive electrode active material and each operation in the preparation of the battery were performed in a dry atmosphere or an argon atmosphere. A dry atmosphere is an air atmosphere with a dew point of −40° C. or less. Some of the examples and comparative examples include cases in which the same operation was performed multiple times to obtain a sufficient amount of sample.

[0071] [Preparation of Positive Electrode Active Material] (Example 1) 2.00 g of Li2O and 0.82 g of LiNiO2 were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and milled at 600 rpm for 48 hours. This yielded the positive electrode active material of Example 1. The ratio of the amount of Ni to the amount of Li is shown in Table 1A.

[0072] Example 2: 2.00 g of LiO and 1.64 g of LiNiO were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 72 hours. This yielded the positive electrode active material of Example 2.

[0073] Example 3: 2.00 g of LiO and 1.63 g of LiNiO were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (Fritsch, P-7 type, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 600 rpm for 100 hours. This yielded the positive electrode active material of Example 3.

[0074] Examples 1 to 3 are examples in which LiNiO2 was used as the nickel source, and the rotation speed of the ball mill and the treatment time by the ball mill were different from one another.

[0075] Example 4: 1.00 g of LiO and 0.83 g of NiO were crushed and mixed in a mortar to obtain a mixture. The mixture was placed in a planetary ball mill (manufactured by Fritsch, PL-7 model, 45 mL container) together with 45 g of zirconia balls (diameter 5 mm), and the mixture was milled at 420 rpm for 150 hours. This yielded the positive electrode active material of Example 4.

[0076] Example 5 A positive electrode active material of Example 5 was prepared in the same manner as in Example 4, except that 1.00 g of Li2O and 0.44 g of NiO were used.

[0077] Example 6 A positive electrode active material of Example 6 was prepared in the same manner as in Example 4, except that 1.00 g of Li2O and 0.63 g of NiO were used.

[0078] Example 7 A positive electrode active material of Example 7 was prepared in the same manner as in Example 4, except that 1.00 g of Li2O and 1.07 g of NiO were used.

[0079] Example 8 A positive electrode active material of Example 8 was prepared in the same manner as in Example 4, except that 1.00 g of Li2O and 1.35 g of NiO were used.

[0080] Example 9 A positive electrode active material of Example 9 was prepared in the same manner as in Example 4, except that 1.00 g of Li2O and 1.67 g of NiO were used.

[0081] Comparative Example 1 A positive electrode active material of Comparative Example 1 was prepared in the same manner as in Example 4, except that 1.00 g of Li2O and 0.28 g of NiO were used.

[0082] [X-ray Diffraction Measurement] Powder X-ray diffraction measurement was performed on the positive electrode active materials of the Examples and Comparative Examples. For the X-ray diffraction measurement, a powder X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation) was used. The measurement conditions are as follows.

[0083] Cu Ka line Detector: HyPix400MF Scan step: 0.02deg Scan speed: 2 deg / min 2θ: 10-80deg Average spectrum of 8 measurements

[0084] 2 shows X-ray diffraction patterns of the positive electrode active materials of Examples and Comparative Examples. "Ex" indicates Examples. "C.Ex" indicates Comparative Examples.

[0085] [Calculation of Integrated Intensity Ratio] The X-ray diffraction pattern of each positive electrode active material was analyzed using analytical software (OriginPro2022, manufactured by OriginLab). That is, the integrated intensity I1 of the first diffraction peak, the integrated intensity I2 of the second diffraction peak, and the integrated intensity I3 of the third diffraction peak were calculated. The calculation results of the integrated intensity ratio I2 / I1 and the integrated intensity ratio I3 / I1 are shown in Table 1A. The Lorentz function or Voigt function was used for curve fitting.

[0086]

[0087] [Observation by Scanning Electron Microscope (SEM)] Fig. 3 shows an SEM image of the positive electrode active material of Example 4. As can be seen from the SEM image, the positive electrode active material of Example 4 had a secondary particle structure. The positive electrode active materials of the other Examples also had a similar secondary particle structure.

[0088] [Measurement of True Density] The true densities of the positive electrode active materials of Examples 4 to 9 and Comparative Example 1 were measured by a pycnometer method. The results are shown in Table 1A. The true densities of the positive electrode active materials of Examples 4 to 9 were 2.2 g / cm 3 3.3g / cm or more 3 It was within the following range:

[0089] [Measurement of Specific Surface Area] The specific surface areas of the positive electrode active materials of Examples 4 to 9 and Comparative Example 1 were measured by the BET method. The results are shown in Table 1A. The specific surface areas of the positive electrode active materials of Examples 4 to 9 were 1.6 m 2 / g or more 60m 2 / g or less.

[0090] [Battery Fabrication] Coin batteries conforming to the CR2016 standard were fabricated using the positive electrode active materials of the Examples and Comparative Examples. The positive electrode consisted of a positive electrode composite containing the positive electrode active material, acetylene black, and polytetrafluoroethylene in a mass ratio of 7:2:1. The negative electrode consisted of a 0.3 mm thick lithium metal foil. The separator consisted of a three-layer separator consisting of nonwoven fabric, polyolefin resin film, and nonwoven fabric.

[0091] The electrolyte solution A used in the battery of Example 1 was prepared as follows: Ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1. Vinylene carbonate was added to the mixture of ethylene carbonate and diethyl carbonate at a ratio of 1% by volume to obtain a mixed solvent. LiPF6 was dissolved in the resulting mixed solvent at a concentration of 1 mol / L to prepare electrolyte solution A.

[0092] Electrolyte solution B was prepared in the same manner as electrolyte solution A, except that the volume ratio of vinylene carbonate in the mixed solvent was changed to 5% by volume. Electrolyte solution C was prepared in the same manner as electrolyte solution A, except that the volume ratio of vinylene carbonate in the mixed solvent was changed to 10% by volume. Electrolyte solution D was prepared in the same manner as electrolyte solution A, except that vinylene carbonate was not used. The effect of differences in the volume ratio of vinylene carbonate on the charge voltage and discharge capacity of the battery is sufficiently small to be negligible compared to the effect of differences in the physical properties of the positive electrode active material on the charge voltage and discharge capacity of the battery.

[0093] The types of electrolytes used in the batteries of the examples and comparative examples are shown in Table 1B.

[0094]

[0095] [Charge / Discharge Test] (Example 1) The battery of Example 1 was charged at a current value of 50 mA / g with an upper voltage limit of 3.3 V and an upper charge capacity limit of 300 mAh / g. The charge capacity, charge voltage at 200 mAh / g, and charge voltage at 300 mAh / g are shown in Table 2. After a 20-minute rest, the upper discharge capacity limit was set to 300 mAh / g, and constant-current discharge was performed at a current value of 50 mA / g down to 1.5 V. Subsequently, discharge was performed at a constant voltage of 1.5 V until a current value of 5 mA / g was reached. The discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V are shown in Table 2.

[0096] The unit of capacity "mAh / g" represents the capacity per 1 g of Li 2 O. The unit of current value "mA / g" represents the current value per 1 g of Li 2 O.

[0097] Example 2 The battery of Example 2 was charged at a current value of 50 mA / g with an upper voltage limit of 3.25 V and an upper charge capacity limit of 300 mAh / g. The charge capacity, charge voltage at 200 mAh / g, and charge voltage at 300 mAh / g are shown in Table 2. After a 20-minute rest, the upper discharge capacity limit was set to 300 mAh / g, and constant-current discharge was performed at a current value of 50 mA / g to 2.0 V. Subsequently, discharge was performed at a constant voltage of 2.0 V until a current value of 5 mA / g was reached. The discharge capacities at voltages of 2.2 V and 2.0 V are shown in Table 2.

[0098] Example 3 The battery of Example 3 was charged at a current value of 44.45 mA / g with an upper voltage limit of 3.4 V and an upper charge capacity limit of 300 mAh / g. The charge capacity, charge voltage at 200 mAh / g, and charge voltage at 300 mAh / g are shown in Table 2. After a 20-minute rest, the upper discharge capacity limit was set to 300 mAh / g, and constant-current discharge was performed at a current value of 44.45 mA / g down to 1.5 V. Discharge was then performed at a constant voltage of 1.5 V. During the discharge process, the specified current value (5 mA / g) was not reached until the discharge capacity exceeded 300 mAh / g. Table 2 shows the discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V.

[0099] (Comparative Example 1) The battery of Comparative Example 1 was charged at a current value of 50 mA / g with an upper voltage limit of 3.2 V and an upper charge capacity limit of 600 mAh / g. After the voltage reached 3.2 V, further charging was performed at a constant voltage of 3.2 V for 24 hours. The charge capacity, charge voltage at 200 mAh / g, and charge voltage at 300 mAh / g are shown in Table 2. After a 20-minute rest, the upper discharge capacity limit was set to 600 mAh / g, and discharge was performed at a current value of 50 mA / g until a discharge capacity of 500 mAh / g was reached. Subsequently, discharge was performed at a constant voltage of 1.5 V until a current value of 5 mA / g was reached. Table 2 shows the discharge capacities at voltages of 2.2 V, 2.0 V, 1.8 V, and 1.5 V.

[0100]

[0101] All of Examples 1 to 3, in which the integrated intensity ratio I / I was 0.48 or greater, exhibited sufficiently large discharge capacities compared to Comparative Example 1, in which the integrated intensity ratio I / I was less than 0.48. The reason the charge voltage of Comparative Example 1 was lower than that of Examples 1 to 3 is that the upper limit voltage of Comparative Example 1 was set to 3.2 V and the upper limit voltage of Examples 1 to 3 was set to 3.4 V, and therefore, in Comparative Example 1, the charge voltage was fixed at the upper limit voltage of 3.2 V when the charge capacity exceeded 200 mAh / g.

[0102] Example 4: The battery of Example 4 was charged at a current of 50 mA / g with an upper voltage limit of 3.4 V and an upper charge capacity limit of 600 mAh / g. The charge capacity, charge voltage at 200 mAh / g, charge voltage at 300 mAh / g, charge voltage at 400 mAh / g, charge voltage at 500 mAh / g, and charge voltage at 600 mAh / g are shown in Table 3A. After a 20-minute rest, the upper discharge capacity limit was set to 600 mAh / g, and constant-current discharge was performed at a current of 50 mA / g down to 1.8 V. Subsequently, discharge was performed at a constant voltage of 1.8 V until a current of 5 mA / g was reached. The discharge capacities at voltages of 2.2 V, 2.0 V, and 1.8 V are shown in Table 3B. The ratio of the discharge capacity at 1.8 V to the charge capacity is shown in Table 3B as the "Coulombic efficiency."

[0103] (Examples 5 to 7) The batteries of Examples 5 to 7 were charged at a current of 50 mA / g with an upper voltage limit of 3.2 V and an upper charge capacity limit of 600 mAh / g. After the voltage reached 3.2 V, further charging was performed at a constant voltage of 3.2 V for 24 hours. The charge capacity, charge voltage at 200 mAh / g, charge voltage at 300 mAh / g, charge voltage at 400 mAh / g, charge voltage at 500 mAh / g, and charge voltage at 600 mAh / g are shown in Table 3A. After a 20-minute rest, the upper discharge capacity limit was set to 600 mAh / g, and constant-current discharge was performed at a current of 50 mA / g to 1.5 V. Subsequently, discharge was performed at a constant voltage of 1.5 V until a current of 5 mA / g was reached. Table 3B shows the discharge capacity at each voltage of 2.2 V, 2.0 V, 1.8 V, and 1.5 V. The ratio of the discharge capacity at a voltage of 1.5 V to the charge capacity is shown in Table 3B as "Coulomb efficiency."

[0104] Comparative Example 1 In addition to the measurement results shown in Table 2, the charge voltages at 400 mAh / g, 500 mAh / g, and 600 mAh / g are shown in Table 3A. The ratio of the discharge capacity at a voltage of 1.5 V to the charge capacity is shown in Table 3B as the "Coulomb efficiency."

[0105] FIG. 4 is a graph showing charge / discharge curves of Example 4 and Comparative Example 1.

[0106]

[0107]

[0108] The batteries of Examples 4 to 7 containing the positive electrode active material using NiO as the nickel source exhibited higher charge capacities than the batteries of Examples 1 to 3 containing the positive electrode active material using LiNiO2 as the nickel source.

[0109] The coulombic efficiency of the batteries of Examples 4 to 7 was significantly higher than that of the battery of Comparative Example 1. In other words, the batteries of Examples 4 to 7 had excellent initial discharge capacities.

[0110] The battery of Comparative Example 1 reached an upper limit voltage of 3.2 V at an early stage (200 mAh / g). In contrast, the batteries of Examples 4 to 7 had charge voltages less than 3.2 V even when charged to a large capacity (e.g., 500 mAh / g). The charge voltages at each capacity of the batteries of Examples 4 to 7 were significantly lower than the charge voltage at each capacity of Comparative Example 1. In other words, the charge voltages of the batteries of Examples 4 to 7 were lower than the charge voltage of the battery of Comparative Example 1.

[0111] (Example 4.1 and Examples 6.1 to 9) The batteries of Example 4.1, Example 6.1, and Example 7.1 were fabricated in the same manner as the batteries of Example 4, Example 6, and Example 7 shown in Tables 3A and 3B, respectively.

[0112] The upper voltage limit was set to 3.2 V, the upper charge capacity limit was set to 800 mAh / g, and the batteries of Examples 4.1 and 6.1 to 9 were charged at a current value of 50 mA / g. After the voltage reached 3.2 V, charging was performed at a constant voltage of 3.2 V for 24 hours. The charge capacity, charge voltage at 200 mAh / g, charge voltage at 300 mAh / g, charge voltage at 400 mAh / g, charge voltage at 500 mAh / g, 600 mAh / g, and 700 mAh / g are shown in Table 4A. After a 20-minute rest, the upper discharge capacity limit was set to 850 mAh / g, and constant-current discharge was performed at a current value of 50 mA / g to 1.5 V. Subsequently, discharging was performed at a constant voltage of 1.5 V until a current value of 5 mA / g was reached. Table 4B shows the discharge capacity at each voltage of 2.2 V, 2.0 V, 1.8 V, and 1.5 V. The ratio of the discharge capacity at a voltage of 1.5 V to the charge capacity is shown in Table 4B as "Coulomb efficiency."

[0113]

[0114]

[0115] The batteries of each example shown in Fig. 4A are batteries containing a positive electrode active material using NiO as the nickel source, and exhibited a higher charge capacity than the batteries of Examples 1 to 3 containing a positive electrode active material using LiNiO as the nickel source.

[0116] The coulombic efficiency of the battery of each example shown in Table 4B was significantly higher than the coulombic efficiency of the battery of Comparative Example 1. In other words, the battery of each example shown in Table 4B had an excellent initial discharge capacity.

[0117] The battery of Comparative Example 1 reached an upper limit voltage of 3.2 V at an early stage (200 mAh / g). In contrast, the batteries of each Example shown in Table 4A had a charge voltage of less than 3.2 V even when charged to a large capacity (e.g., 500 mAh / g). In other words, the charge voltage of the batteries of each Example shown in Table 4A was lower than the charge voltage of the battery of Comparative Example 1.

[0118] As shown in Tables 4A and 4B, the batteries of Examples 4.1, 6.1, and 7.1 exhibited low charge voltages and large discharge capacities even when the charge and discharge conditions were changed. The batteries of Examples 8 and 9 also exhibited low charge voltages and large discharge capacities.

[0119] [X-ray Absorption Fine Structure Measurement] The X-ray absorption fine structure (XAFS) of the positive electrode active materials of Examples 1 and 4 was measured at a synchrotron radiation facility (SPring-8) under the following measurement conditions.

[0120] Beamline: 16B2 Method: Transmission XAFS using a monochromator Detector: Ion chamber Wavelength calibration: Calibrate the Cu pre-edge to 12.7190 deg Beam size: length x width = 1.5 mm x 4 mm

[0121] The positive electrode active material of Example 1 was prepared in the following four states (a1) to (d1) and measured. The positive electrode active material (b1) is considered to be in the "charged state," and the positive electrode active material (c1) is considered to be in the "discharged state." (a1) Immediately after preparation (pristine) (b1) Charged at a constant current of 26.5 mA / g over 20 hours to a charge capacity of 530 mAh / g (charged state) (c1) Discharged from the charged state at a constant current of 26.5 mA / g to a voltage of 2.26 V (discharged state) (d1) Discharged from the charged state at a constant current of 26.5 mA / g to a voltage of 1.00 V

[0122] For the positive electrode active material of Example 4, the following three states (a2) to (c2) were prepared and measured. By repeating charge and discharge, for (b2), the first cycle charge state, the second cycle charge state, the third cycle charge state, and the fourth cycle charge state were prepared and measured, respectively. For (c2), the first cycle discharge state, the second cycle discharge state, and the third cycle discharge state were prepared and measured, respectively. (a2) Immediately after preparation (pristine) (b2) Charged at a constant current of 50 mA / g over 12 hours to a charge capacity of 600 mAh / g (charged state) (c2) Discharged from the charged state to a voltage of 1.5 V at a constant current of 50 mA / g, and then discharged at a constant voltage of 1.5 V to a discharge capacity of 600 mAh / g (discharged state)

[0123] FIG. 6A is an XAFS spectrum of the positive electrode active material of Example 1. FIG. 6B is a XANES (X-ray absorption near edge structure) spectrum of the positive electrode active material of Example 1. FIG. 6C is a graph showing the valence of nickel calculated from the XANES spectrum of FIG. 6B. FIG. 7A is an XAFS spectrum of the positive electrode active material of Example 4. FIG. 7B is a XANES spectrum of the positive electrode active material of Example 4. FIG. 7C is a graph showing the valence of nickel calculated from the XANES spectrum of FIG. 7B. The valence of nickel was calculated from the position of the absorption edge of the XANES spectrum by the method described below.

[0124] FIG. 8 shows the process of calculating the valence of nickel from the absorption edge position of the XANES spectrum. As shown in FIG. 8, for Example 1, a range of 0.4 to 1.4 was selected for the vertical axis (normalized X-ray absorption), and a rectangle was defined with an area equal to the integral value (area of ​​the gray portion) obtained by integrating horizontally. The energy corresponding to the side of the rectangle on the high-energy side was regarded as the K-absorption edge energy (eV). For Example 4, a range of 0.2 to 1.2 was selected for the vertical axis, and a rectangle was defined with an area equal to the integral value obtained by integrating horizontally. The energy corresponding to the side of the rectangle on the high-energy side was regarded as the K-absorption edge energy. Among standard materials with known valences, the XANES spectra of divalent NiO and trivalent LiNiO were used to determine the K-absorption edge energy using the same method as in Examples 1 and 4. The calibration curves shown in FIGS. 6C and 7C were created from the K-absorption edge energies of the standard materials. The K-absorption edge energy was determined from the XANES spectra of the positive electrode active material of Example 1 in each of the (a1), (b1), and (c1) states, and plotted on the calibration curve of FIG. 6C. The K-absorption edge energy was determined from the XANES spectra of the positive electrode active material of Example 4 in each of the (a2), (b2), and (c2) states, and plotted on the calibration curve of FIG. 7C. The Ni valence in each state is determined from the vertical axis. The calibration curve equations in FIGS. 6C and 7C differ because the experimental dates are different, resulting in slight differences in the brightness of the incident X-rays, the monochromaticity of the incident X-rays, the sensitivity of the detector, and other factors, resulting in differences in the shape of the XANES spectra. Therefore, it is necessary to obtain the XANES spectrum of a standard material on each experimental day and determine the calibration curve. Even on the same day, there was concern that differences in the brightness of the incident X-rays, the monochromaticity of the incident X-rays, the sensitivity of the detector, etc. might have occurred between the start and end of the experiment. Therefore, in the experiment shown in Figure 6C, measurements were taken twice for the standard materials NiO and LiNiO2, once at the start and once at the end of the experiment. For LiNiO2, there was some variation between the two measurements. For NiO, the two measurements were nearly identical.

[0125] 6C , the valence of the positive electrode active material of Example 1 exceeded 3 immediately after preparation (a1), in a charged state (b1), and in a discharged state (c1). The valence changed with charge and discharge, but the range was narrow.

[0126] As shown in FIG. 7C , the valence of the positive electrode active material of Example 4 was below trivalent immediately after preparation (a2) and in a discharged state (c2). Specifically, the valence of the positive electrode active material of Example 4 was between 2.0 and 2.5 immediately after preparation and in a discharged state. In a charged state (b2), the valence of the positive electrode active material of Example 4 exceeded 3.0. The valence of the positive electrode active material of Example 4 changed significantly with charge and discharge. Because the positive electrode active material of Example 4 showed better results than the positive electrode active material of Example 1, it is believed that good results can be obtained when the nickel valence in a discharged state is 3.0 or less.

[0127] The technology of the present disclosure is useful for batteries such as lithium secondary batteries.

Claims

1. A positive electrode active material comprising: lithium oxide having an inverse fluorite crystal structure and having nickel dissolved therein; and a metal oxide containing nickel, wherein in an X-ray diffraction pattern measured using Cu-Kα radiation, a diffraction peak attributable to the metal oxide containing nickel is present in a diffraction angle 2θ range of 40° to 50°, and the ratio of the integrated intensity of a second diffraction peak attributable to a (220) plane of the lithium oxide present in the diffraction angle 2θ range of 52° to 62° to the integrated intensity of a first diffraction peak attributable to a (111) plane of the lithium oxide present in the diffraction angle 2θ range of 30° to 40° is 0.48 or more.

2. The positive electrode active material according to claim 1, wherein a ratio of an integrated intensity of a third diffraction peak attributable to a crystal plane of the nickel-containing metal oxide present in the diffraction angle 2θ range of 40° to 50° to the integrated intensity of the first diffraction peak is 0.37 or more and 15.67 or less.

3. The positive electrode active material according to claim 1, wherein the valence of nickel contained in the positive electrode active material is 3.0 or less in a discharged state.

4. The positive electrode active material according to claim 1, wherein the positive electrode active material has a secondary particle structure composed of a plurality of primary particles of the lithium oxide and a plurality of primary particles of the nickel-containing metal oxide.

5. The positive electrode active material according to claim 1, wherein a ratio of the amount of nickel contained in said positive electrode active material to the amount of lithium contained in said positive electrode active material is 0.058 or more and 0.350 or less.

6. The true density of the positive electrode active material is 2.2 g / cm 3 3.3g / cm or more 3 The positive electrode active material according to claim 1 , wherein:

7. The specific surface area of ​​the positive electrode active material is 1.6 m 2 / g or more 60m 2 The positive electrode active material according to claim 1 , wherein the Mo content is 0.1 to 0.5% by mass %.

8. A battery comprising a positive electrode containing the positive electrode active material according to claim 1.

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