Alkali metal-containing oxide, positive electrode active material, electrode and battery

Abstract

To provide an alkali metal-containing oxide excellent in charge / discharge capacity and coulomb efficiency.SOLUTION: An alkali metal-containing oxide has a spinel-type structure and is represented by general formula (1), wherein a peak having a half-width at 2θ of 0.5 to 5° is observed within a range of 40 to 45° in X-ray diffraction chart measured using CuKα rays at 25°C for the alkali metal-containing oxide: AxM'aM''bZcO4-eXd (1) (in formula (1), 1.1<x≤2.8, 0.8≤a<1.9, 0.05<b≤0.6, 1.0≤a+b<2.0, 0≤c<0.2, 0≤d<1.0, and 0≤e<1.0, where A is an alkali metal element, M' is selected from Ti, Cr, Mn, Fe, Co, Ni, and Cu, M'' is selected from Si, P, S, Ge, and V, Z is another element, and X is a halogen element).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an alkali metal-containing oxide, a positive electrode active material, an electrode, and a battery. [Background technology]

[0002] Secondary batteries are known that charge and discharge by the movement of alkali metal ions between a positive electrode and a negative electrode. Among such secondary batteries, lithium-ion secondary batteries are representative. These batteries have already been put to practical use as small power sources for mobile phones and laptops, and are also expected to be used as large-scale power sources for electric vehicles, hybrid vehicles, and other vehicles, as well as for distributed power storage systems. Demand for lithium-ion secondary batteries is growing.

[0003] Alkali metal-containing oxides with a spinel-type crystal structure are known for use as positive electrodes in the secondary batteries. Such alkali metal-containing oxides, such as LiMn2O4, have 32 oxide ions in one unit cell, with 8 tetrahedral sites occupied by alkali metal ions and 16 octahedral sites occupied by transition metal ions. Alkali metal-containing oxides with an excess alkali metal content, in which the ratio of alkali metal elements per 4 oxygen atoms is greater than 1 and the ratio of transition metal elements per 4 oxygen atoms is less than 2, are also known (Patent Documents 1 to 6). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 07-122299 [Patent Document 2] Special Publication No. 2000-500280 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-063123 [Patent Document 4] Chinese Patent Application Publication No. 102163716 [Patent Document 5] Chinese Patent Application Publication No. 103594700 [Patent Document 6] Special Publication No. 2014-525667 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is room for improvement in the charge / discharge capacity of the spinel-type alkali metal-containing oxide.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide an alkali metal-containing oxide having excellent charge / discharge capacity, and an electrode and a battery containing such an alkali metal oxide. [Means for solving the problem]

[0007] The alkali metal-containing oxide of the present invention has a spinel structure and a composition represented by the following general formula (1), and in an X-ray diffraction chart measured on the alkali metal-containing oxide at 25°C using CuKα radiation, a peak with a half-width of 0.5 to 5° in 2θ is observed within a range of 40 to 45° in 2θ. A x M' a M'' b Z c O 4-e X d ···(1) (In formula (1), 1.1 <x≦2.8、0.8≦a≦1.9、0.05<b≦0.6、1.0≦a+b<2.0、0≦c<0.2、0≦d<1.0、0≦e<1.0であり、 A is an alkali metal element, M' is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu; M″ is at least one selected from the group consisting of Si, P, S, Ge, and V; Z is an element of Groups 2 to 16 of the periodic table other than oxygen, M', and M''; X is a halogen element.

[0008] The alkali metal-containing oxide is prepared by preparing an electrochemical cell including an electrode containing the alkali metal-containing oxide, a counter electrode of lithium metal, and an electrolyte solution containing a lithium salt disposed between the electrode and the counter electrode, and the Li / Li + When the battery is charged to 4.8 V as a standard and then discharged to 1.5 V, x in general formula (1) may be in the range of 2.2 to 2.8.

[0009] In the above general formula (1), A may contain Li.

[0010] In the above general formula (1), M'' may contain V.

[0011] In the above general formula (1), 1.1 <x≦2.0であってよい。

[0012] The electrode of the present invention contains the alkali metal-containing oxide.

[0013] The nonaqueous secondary battery of the present invention comprises the above electrode as a positive electrode and a negative electrode containing lithium. [Effects of the Invention]

[0014] The present invention has been made in view of the above circumstances, and has as its object to provide an alkali metal-containing oxide that is excellent in charge / discharge capacity and coulombic efficiency, and an electrode and a battery that contain such an alkali metal oxide. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an X-ray diffraction chart of the lithium-containing oxides of Examples 1 to 4. [Figure 2] FIG. 2 is an X-ray diffraction chart of the lithium-containing oxides of Examples 5 to 8. [Figure 3] FIG. 3 is an X-ray diffraction chart of the lithium-containing oxides of Examples 9 and 10 and Comparative Examples 1 to 3. [Figure 4]FIG. 4 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 1 and 3 to 6. [Figure 5] FIG. 5 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 2, 7 and 8. [Figure 6] FIG. 6 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 9 and 10. [Figure 7] FIG. 7 is a graph showing the initial charge-discharge curves of Comparative Examples 1 to 3. [Figure 8] FIG. 8 is a graph showing the initial charge-discharge curves of Example 4 and Comparative Example 2, with the horizontal axis representing the lithium composition ratio x (i.e., x in the composition formula LixMn1.4V0.3O4) when the amount of oxygen in the composition of the alkali metal-containing oxide, which is the positive electrode active material, is set to 4, and the vertical axis representing the battery voltage. [Figure 9] FIG. 9 is a diagram showing an electron beam diffraction image of the sample of Example 5. [Figure 10] FIG. 10 is a diagram showing a dark-field observation image of the sample of Example 5 observed with a transmission electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0016] The alkali metal-containing oxide of this embodiment has a spinel structure and a composition represented by the following general formula (1), and in an X-ray diffraction chart measured on the alkali metal oxide at 25°C using CuKα radiation, a peak with a half-width of 0.5 to 5° in 2θ is observed within a range of 40 to 45° in 2θ. A x M' a M'' b Z c O 4-e X d ···(1) (In formula (1), 1.1 <x≦2.8、0.8≦a≦1.9、0.05<b≦0.6、1.0≦a+b<2.0、0≦c<0.2、0≦d<1.0、0≦e<1.0であり、 A is an alkali metal element, M' is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu; M″ is at least one selected from the group consisting of Si, P, S, Ge, and V; Z is an element of Groups 2 to 16 of the periodic table other than oxygen, M', and M''; X is a halogen element.

[0017] A is not particularly limited as long as it is an alkali metal element, but may contain at least one selected from the group consisting of Li, Na, K, Rb, and Cs, may contain at least one selected from the group consisting of Li, Na, and K, may contain at least one of Li and Na, or may contain Li.

[0018] Of the total amount of alkali metals contained in the alkali metal-containing oxide of this embodiment, the content of one alkali metal may be 90 mol% or more, 95 mol% or more, 98 mol% or more, 99 mol% or more, or 99.9 mol% or more, or may contain substantially only one alkali metal (i.e., the content of alkali metals other than the one alkali metal is substantially 0 mol%). The one alkali metal may be Li, Na, or K, or may be Li and / or Na, or may be Li. When the alkali metal-containing oxide mainly contains Li (for example, when the content of one alkali metal is 80 mol% or more of the total amount of alkali metals contained in the alkali metal-containing oxide), a peak with a half-width of 0.5 to 5° in 2θ tends to be observed in the X-ray diffraction chart within a range of 43 to 45° in 2θ.

[0019] In formula (1), x may be greater than 1.1 and equal to or less than 2, may be 1.13 to 2.75, may be 1.15 to 2.7, may be 1.2 to 2.6, or may be 1.25 to 2.5. Also, x may be 1.13 to 2.1, may be 1.15 to 2.0, may be 1.2 to 1.95, or may be 1.25 to 1.9.

[0020] M' may contain at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu, may contain at least one of Cr, Mn, and Ni, may contain at least one of Mn and Ni, or may contain Mn.

[0021] M'' may contain at least one element selected from the group consisting of Si, P, S, Ge and V, may contain at least one of P and V, and may contain V.

[0022] a may be 0.9 to 1.9, or may be 1.0 to 1.85, and b may be 0.06 to 0.58, or may be 0.08 to 0.55, or may be 0.1 to 0.5.

[0023] a+b may be 1.2 to 1.95, or may be 1.5 to 1.93.

[0024] Z is an element of Groups 2 to 16 of the periodic table other than oxygen, M' and M'' and examples thereof include Al, Mg, Ca, Zr, Nb, Mo, Ru, W, and Sn.

[0025] c may be 0.1 or less, 0.05 or less, 0.01 or less, or substantially 0.

[0026] X may contain at least one element selected from the group consisting of F, Cl, Br and I, may contain at least one of F and Cl, and may contain F.

[0027] d may be 0.8 or less, 0.6 or less, 0.4 or less, 0.2 or less, 0.05 or less, or 0.01 or less. d may be 0.001 or more, or 0. d may be 0.001 to 0.8, 0.001 to 0.6, or 0.001 to 0.2. e may be 0.8 or less, 0.6 or less, 0.4 or less, 0.2 or less, 0.05 or less, 0.01 or less, or 0. e may be 0.001 or more. e may be 0.001 to 0.8, 0.001 to 0.6, or 0.001 to 0.2.

[0028] The half width of the X-ray diffraction peak observed within the above range of 40 to 45° may be 0.7 to 4.5°, 0.9 to 4.0°, 1.0 to 3.8°, or 1.28 to 3.5°.

[0029] In the alkali metal-containing oxide of this embodiment, a peak having a half width of 0.5 to 8 degrees 2θ may be observed in the range of 63 to 66 degrees 2θ in the X-ray diffraction chart. The half width of the peak may be 1.0 to 7.5 degrees.

[0030] The alkali metal-containing oxide of this embodiment may have both a crystalline phase and an amorphous phase. The crystalline phase may be dispersed within the amorphous phase. The presence of the amorphous phase tends to improve the diffusion of lithium ions within the material. The alkali metal-containing oxide of this embodiment may have a crystalline phase (crystallites) having an average particle size of 1 to 30 nm in equivalent circle diameter. The average particle size of the crystalline phase (crystallites) may be 1 to 20 nm, or 1 to 15 nm in equivalent circle diameter. Here, the amorphous phase can be confirmed by observation with a transmission electron microscope (TEM).

[0031] The alkali metal-containing oxide of this embodiment may contain 8 to 15 mass% Li, 32 to 57 mass% of element M', which is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu, and 3 to 30 mass% of element M", which is at least one element selected from the group consisting of Si, P, S, Ge, and V. In an X-ray diffraction chart measured at 25°C using CuKα radiation, a peak pattern attributable to a spinel structure and a peak with a half width of 0.5 to 5° are observed within a 2θ range of 40 to 45°. The lithium-containing oxide may contain oxygen, an element Z of Groups 2 to 16 of the periodic table other than M' and M" Specific examples of element Z include those exemplified as Z in the general formula (1) above. The content of Z may be 20 mass% or less, 10 mass% or less, 5 mass% or less, 1 mass% or less, or substantially 0 mass% based on the total amount of the alkali metal-containing oxide. The alkali metal-containing oxide may also contain a halogen element, and examples of the halogen element include those exemplified as X in the general formula (1) above. The content of the halogen element may be 20 mass% or less, 10 mass% or less, 5 mass% or less, 1 mass% or less, or substantially 0 mass% relative to the total amount of the alkali metal-containing oxide. The alkali metal-containing oxide may be a single phase or a layer-containing oxide, and peaks other than those attributed to a spinel structure may be observed in an X-ray diffraction test. The alkali metal-containing oxide may have a crystalline phase (crystallites) and an amorphous phase.

[0032] The method for producing the alkali metal-containing oxide is not particularly limited, but examples thereof include a method in which a spinel-type oxide containing Li and M' and a lithium salt containing M'' are mechanochemically mixed in a ball mill. Examples of spinel-type oxides include LiMnTiO4, LiCrMnO4, LiMn2O4, LiFeMnO4, LiCoMnO4, and LiNi 0.5 Mn 1.5 O4, LiCu 0.5 Mn 1.5Lithium salts include Li3VO4, Li4SiO4, Li2SiO3, and Li3P 0.5 V 0.5 Examples of suitable raw materials include LiO, LiGeO, LiSO, and the like. Also, alkali metal oxides such as LiO, and oxides of M' or M" such as VO, GeO, and SiO can be used as raw materials. The raw materials are not limited to the above, and compounds containing at least one of Li, M', and M" and oxygen may be blended to achieve the desired composition. The conditions for the ball mill are not particularly limited, and the rotation speed may be 100 to 700 rpm, and the mixing time may be 0.5 to 72 hours or 10 to 60 hours. The mixing time may be 20 to 72 hours or 30 to 60 hours. When X in general formula (1) is introduced, an alkali metal salt of X may also be used as a raw material.

[0033] The alkali metal-containing oxide of this embodiment can be used as a material for batteries (lithium ion batteries, sodium ion batteries, etc.). That is, the battery of this embodiment contains the lithium-containing oxide. The battery may be a primary battery or a secondary battery. The battery may also be a nonaqueous secondary battery. In the battery, the lithium-containing oxide may be contained in an electrode.

[0034] The battery of this embodiment has a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode.

[0035] The positive electrode of this embodiment includes a current collector and a positive electrode mixture carried on the current collector. The positive electrode mixture may form a positive electrode mixture layer on the current collector.

[0036] The positive electrode mixture contains the lithium-containing oxide, and may contain, as necessary, a conductive material (conductive assistant), a binder, etc. In other words, the lithium oxide may be contained in the positive electrode active material.

[0037] Conductive materials include carbon materials such as natural graphite, artificial graphite, coke, carbon black, and acetylene black. Binders include thermoplastic resins, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers; as well as polyolefin resins such as polyethylene and polypropylene. Current collectors can be made of aluminum, nickel, stainless steel, or other materials.

[0038] Examples of methods for supporting the positive electrode mixture on the current collector include pressure molding, forming a paste from the electrode mixture using an organic solvent, applying the paste to the current collector, drying, and then pressing to adhere the paste to the current collector. For example, when forming a paste, a slurry containing the positive electrode active material, a conductive material, a binder, and an organic solvent is prepared. Examples of organic solvents include amines such as N,N-dimethylaminopropylamine and diethyltriamine; ethers such as ethylene oxide and tetrahydrofuran; ketones such as methyl ethyl ketone; esters such as methyl acetate; and aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Examples of methods for applying the electrode mixture to the current collector include slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

[0039] The negative electrode of the battery is not particularly limited and may contain a negative electrode active material and, if necessary, a conductive additive, a binder, etc. Examples of negative electrode active materials for lithium-ion batteries include simple elements such as Li, Si, P, Sn, Si-Mn, Si-Co, Si-Ni, In, and Au, alloys or composites containing these elements, carbon materials such as graphite, and materials in which lithium ions are inserted between the layers of the carbon material. In the case of a negative electrode of a sodium-ion battery, a material in which Li in the material listed as a negative electrode material for a lithium-ion battery is replaced with Na can be used as the negative electrode material.

[0040] The electrolyte of the battery is not particularly limited, and an electrolytic solution in which an alkali metal salt is dissolved in an organic solvent can be used. Alternatively, the electrolyte may be a solid electrolyte. Examples of the alkali metal salt include iodide salts, tetrafluoroborate salts, hexafluorophosphate salts, bis(fluorosulfonyl)imide salts, and bis(trifluoromethylsulfonyl)imide salts.

[0041] The organic solvent contained in the electrolytic solution is not particularly limited, but examples thereof include non-aqueous solvents, such as cyclic carbonate esters such as ethylene carbonate (EC) or propylene carbonate (PC), linear carbonate esters such as dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC), or sultones, etc. The solvents may be used alone or in combination of two or more.

[0042] The alkali metal-containing oxide of this embodiment has excellent alkali metal ion occlusion ability. Therefore, the alkali metal-containing oxide of this embodiment can be used by preparing an electrochemical cell including an electrode containing the alkali metal-containing oxide, a counter electrode of lithium metal, and an electrolyte containing a lithium salt disposed between the electrode and the counter electrode, and then performing Li / Li +When the battery is charged to 4.8 V (initial charge) and then discharged to 1.5 V, x in general formula (1) may be in the range of 2.2 to 2.8. After the initial charge and discharge, x may be 2.25 to 2.7, 2.3 to 2.6, or 2.35 to 2.55.

[0043] The positive electrode active material of this embodiment includes a composite oxide containing an alkali metal element, an element M', and an element M" and includes 8 to 27 mass% of the alkali metal element, 26 to 57 mass% of element M', which is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu, and 2 to 30 mass% of element M", which is at least one element selected from the group consisting of Si, P, S, Ge, and V. In an X-ray diffraction chart of the positive electrode active material measured at 25°C using CuKα radiation, a peak pattern attributable to a spinel structure derived from the composite oxide is observed, and a peak with a half width of 0.5 to 5° is observed within a 2θ range of 40 to 45°. The composite oxide included in the positive electrode active material may contain the alkali metal-containing oxide described above. The positive electrode active material may have a crystalline phase (crystallites) of the composite oxide and an amorphous phase.

[0044] The present invention includes the following exemplary embodiments. Embodiment 1 An alkali metal-containing oxide having a spinel structure and a composition represented by the following general formula (1): The alkali metal-containing oxide has a peak having a half-width of 0.5 to 5° in 2θ within a range of 40 to 45° in an X-ray diffraction chart measured at 25°C using CuKα radiation. A x M' a M'' b Z c O 4-e X d ···(1) (In formula (1), 1.1 <x≦2.8、0.8≦a<1.9、0.05<b≦0.6、1.0≦a+b<2.0、0≦c<0.2、0≦d<1.0、0≦e<1.0であり、 A is an alkali metal element, M’ is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu, M’’ is at least one selected from the group consisting of Si, P, S, Ge, and V, Z is an element of Groups 2 to 16 of the periodic table other than oxygen, M’, and M’’, X is a halogen element.) Embodiment 2 The alkali metal-containing oxide is used to fabricate an electrochemical cell including an electrode containing the alkali metal-containing oxide, a counter electrode of lithium metal, and an electrolytic solution containing a lithium salt disposed between the electrode and the counter electrode. When the electrochemical cell is charged up to 4.8 V and then discharged down to 1.5 V with respect to the Li / Li + reference, the value of x in the general formula (1) falls within the range of 2.2 to 2.8, which is the alkali metal-containing oxide of Embodiment 1. Embodiment 3 In the general formula (1), A contains Li, which is the alkali metal-containing oxide of Embodiment 1 or 2. Embodiment 4 In the general formula (1), M’’ contains V, which is the alkali metal-containing oxide according to any one of Embodiments 1 to 3. Embodiment 5 In the general formula (1), 1.1 < x ≤ 2.0, which is the alkali metal-containing oxide according to any one of Embodiments 1 to 4. Embodiment 6 The alkali metal-containing oxide according to any one of Embodiments 1 to 5 having an amorphous phase. Embodiment 7 An electrode including the alkali metal-containing oxide according to any one of Embodiments 1 to 6. Embodiment 8 A battery including the electrode according to Embodiment ⑦ as a positive electrode and a negative electrode containing lithium. Embodiment 9 A positive electrode active material including a composite oxide containing an alkali metal element, an element M’, and an element M’’, A positive electrode active material comprising 8 to 15 mass% of an alkali metal element, 32 to 57 mass% of element M', which is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu, and 3 to 30 mass% of element M'', which is at least one element selected from the group consisting of Si, P, S, Ge, and V, wherein an X-ray diffraction chart of the positive electrode active material measured at 25°C using CuKα radiation shows a peak pattern attributable to a spinel structure derived from the composite oxide, and also shows a peak with a half width of 0.5 to 5° within a 2θ range of 40 to 45°. Embodiment 10 The cathode active material of embodiment 9, having an amorphous phase. Embodiment 11 An alkali metal-containing oxide having a crystalline phase having a spinel structure and an amorphous phase, and having a composition represented by the following general formula (1): The alkali metal-containing oxide has a peak having a half-width of 0.5 to 5° in 2θ within a range of 40 to 45° in an X-ray diffraction chart measured at 25°C using CuKα radiation. A x M' a M'' b Z c O 4-e X d ···(1) (In formula (1), 1.1 <x≦2.8、0.8≦a<1.9、0.05<b≦0.6、1.0≦a+b<2.0、0≦c<0.2、0≦d<1.0、0≦e<1.0であり、 A is an alkali metal element, M' is at least one element selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu; M″ is at least one selected from the group consisting of Si, P, S, Ge, and V; Z is an element of Groups 2 to 16 of the periodic table other than oxygen, M', and M''; X is a halogen element. [Example]

[0045] Example 1 The raw materials LiMn2O4 powder and Li3VO4 powder were produced as follows. First, lithium carbonate (FUJIFILM Wako Pure Chemical Corporation) and manganese(IV) oxide (FUJIFILM Wako Pure Chemical Corporation) were mixed in a molar ratio of 1:4 and calcined in air at 800°C for 18 hours to obtain LiMn2O4 powder.Also, lithium carbonate (FUJIFILM Wako Pure Chemical Corporation) and vanadium(V) oxide (FUJIFILM Wako Pure Chemical Corporation) were mixed in a molar ratio of 3:1 and calcined in air at 650°C for 12 hours to obtain Li3VO4 powder.

[0046] The obtained LiMn2O4 powder and Li3VO4 powder were mixed in a molar ratio of 0.9:0.1, and the mixed powder was introduced into a zirconia ball mill container with 4 mm diameter zirconia balls so that the mass ratio of the mixed powder was 65:1. The ball mill container was introduced into a planetary ball mill (Retsch, PM200), and ball milling was performed at a rotation speed of 500 rpm for 48 hours to obtain a lithium-containing oxide.

[0047] (Examples 2 to 6 and Comparative Example 3) As shown in Table 1, lithium-containing oxides were produced in the same manner as in Example 1, except that the blending amounts of the raw materials LiMn2O4 powder and Li3VO4 powder and / or the mixing time were changed.

[0048] Example 7 As raw materials, LiNi 0.5 Mn 1.5 A lithium-containing oxide was produced in the same manner as in Example 1, except that O4 powder and Li3VO4 powder were used in a molar ratio of 0.8:0.2. In addition, LiNi 0.5 Mn 1.5The O4 powder was prepared by weighing out lithium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), nickel(II) oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and manganese(IV) oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in a molar ratio of 1:1:3, mixing them in a wet ball mill with ethanol and 8 mm diameter zirconia balls, filtering, drying, and then calcining the mixed powder in air at 600°C for 15 hours.

[0049] Example 8 The raw materials are LiMn2O4 powder and Li3V 0.5 P 0.5 A lithium-containing oxide was produced in the same manner as in Example 1, except that the O4 powder was used in a molar ratio of 0.8:0.2. In addition, Li3V 0.5 P 0.5 The O4 powder was obtained by mixing lithium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), diammonium hydrogen phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and vanadium (V) oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in a molar ratio of 6:2:1 and calcining the mixture at 800°C in air for 10 hours.

[0050] (Examples 9 and 10) A lithium-containing oxide was produced in the same manner as in Example 1, except that LiCrMnO4 powder and Li3VO4 powder were used in the molar ratio shown in Table 1 as raw materials. LiCrMnO4 was obtained by mixing lithium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), chromium(III) oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and manganese(III) oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) in a molar ratio of 1:1:1, calcining the mixture in air at 800°C for 6 hours, and then calcining it further in air at 900°C for 12 hours.

[0051] (Comparative Example 1) A lithium-containing oxide was produced in the same manner as in Example 1, except that only the LiMn2O4 powder was subjected to ball milling.

[0052] (Comparative Example 2) The LiMn₂O₄ powder of the raw material produced in Example 1 was used as it was.

[0053] <X-ray Diffraction> Powder X-ray diffraction measurements were performed on each lithium-containing oxide of the examples and comparative examples using a powder X-ray diffractometer (manufactured by Rigaku Corporation, Ultima IV). The measurements were carried out at room temperature (25 °C). The above lithium-containing oxide was filled into the depression of a glass plate, and the glass plate on which the sample was placed was sealed in an airtight sample stage with a beryllium window to avoid air and moisture, and the measurement was performed without exposure to the atmosphere. Using a CuKα radiation source, with an output of 40 kV and 40 mA, the range of diffraction angle 2θ = 10° to 90° was scanned at a step of 0.02° and a speed of 2° / min. The peak positions and half-value widths of the peaks observed at 40 - 45° (2θ) are shown in Tables 1 and 2. Figure 1 is the X-ray diffraction chart of the lithium-containing oxides of Examples 1 to 4. Figure 2 is the X-ray diffraction chart of the lithium-containing oxides of Examples 5 to 8. Figure 3 is the X-ray diffraction chart of the lithium-containing oxides of Examples 9 and 10, and Comparative Examples 1 to 3. As can be seen from Figures 1 to 3, the lithium-containing oxides of Examples 1 to 10 showed the same diffraction pattern as Comparative Example 2.

[0054]

Table 1

[0055]

Table 2

[0056] <Charge and Discharge Test> (1) Preparation of the Positive Electrode The lithium-containing oxides (positive electrode active materials) of Examples 1 to 10 and Comparative Examples 1 and 3, acetylene black (product name: HS-100, manufactured by Denka Co., Ltd.) as a conductive material, and polytetrafluoroethylene (PTFE, product number: 6-J, manufactured by Mitsui-Chemours Fluoroproducts Co., Ltd.) as a binder were weighed out to a mass ratio of 70:20:10 (positive electrode active material: conductive material: binder). First, the positive electrode active material and conductive material were thoroughly mixed in an agate mortar, and the binder was added and further mixed. 7 mg of the mixture was weighed out and rolled into a circle on the mortar. The rolled mixture was pressed onto a 110 μm-thick aluminum mesh (100 mesh, manufactured by Nilaco Corporation) as a current collector to obtain positive electrodes containing the positive electrode active material. For Comparative Example 2, a lithium-containing oxide (positive electrode active material), acetylene black (product name: HS-100, manufactured by Denka Co., Ltd.), and an N-methyl-2-pyrrolidone (NMP) solution of PVDF (KF Polymer, product number: L#1120, manufactured by Kureha Corporation) as a binder were added and kneaded in a ratio of 85:10:5 (mass ratio) of positive electrode active material: acetylene black: PVDF to prepare a paste-like positive electrode composite. During the preparation of the positive electrode composite, the viscosity of the paste was adjusted by adding NMP. The obtained positive electrode composite was applied to a 40 μm-thick Al foil as a current collector, dried in the air at 60°C for 1 hour, and then vacuum-dried at 150°C for 8 hours. A circular cathode with a diameter of 14.5 mm was obtained by punching.

[0057] (2) Fabrication and evaluation of Li half-cell A CR2032 coin-type battery was assembled using the above-mentioned positive electrode, a polyethylene porous film (16 μm thick) as a separator, a 1 M LiPF solution as a nonaqueous electrolyte (the solvent was a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35), and metallic lithium as a counter electrode. The battery was assembled in a glove box under an argon atmosphere. Using the prepared coin-type battery, a charge-discharge test was performed under the following conditions at 25°C, in the voltage range of 1.5 to 4.8 V for Examples 1 to 8 and Comparative Examples 1 to 3, and in the voltage range of 1.5 to 4.5 V for Examples 9 and 10. The measurement results of the initial discharge energy density and energy efficiency are shown in Table 3. Charge and discharge conditions: constant current constant voltage charging (CC-CV) was performed at 30 mA / g, with a cutoff condition of 6 mA / g. Discharge conditions: constant current (CC) discharge was performed at 30 mA / g.

[0058] [Table 3]

[0059] FIG. 4 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 1, and 3 to 6. FIG. 5 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 2, 7, and 8. FIG. 6 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 9 and 10. FIG. 7 is a graph showing the initial charge-discharge curves of Comparative Examples 1 to 3. In FIGS. 4 to 7, the horizontal axis shows the capacity of the positive electrode active material, and the vertical axis shows the battery voltage. FIG. 8 is a graph showing the initial charge-discharge curves of Example 4 and Comparative Example 2, with the horizontal axis showing the lithium composition ratio x (that is, the lithium composition ratio in the composition formula Li) when the amount of oxygen in the composition of the alkali metal-containing oxide, which is the positive electrode active material, is set to 4. x Mn 1.4 V 0.3 The graph in Fig. 8 shows the state before the start of charging, and the composition of the lithium-containing oxide contained in the positive electrode at this time is Li 1.6 Mn 1.4 V 0.3After that, the charge-discharge test was carried out, and the composition of the lithium-containing oxide at the time of reaching B (at the end of discharge) in Figure 8 was calculated as Li 2.45 Mn 1.4 V 0.3 O4, and it is clear that it has excellent lithium ion absorption capacity.

[0060] <Observation by transmission electron microscope> The measurement was carried out under the following conditions. Equipment: Analytical electron microscope ARM200F manufactured by JEOL Ltd. Measurement conditions: Accelerating voltage 200kV Sample preparation: The lithium-containing oxide of Example 5 was subjected to sample preparation by a dry dispersion method under an inert atmosphere. Figure 9 shows an electron beam diffraction image of the sample of Example 5. The circle indicated by BF in the figure is the observation position of a bright-field image (not shown). Circles 1, 2, and 3 in Figure 9 indicate the insertion position (aperture) of the objective aperture. In Figure 9, multiple bright spots are observed arranged in a ring shape, and a halo is also observed, indicating the presence of a crystalline phase and an amorphous phase. Figure 10 shows a dark-field image of the sample of Example 5 observed by a transmission electron microscope. (A), (B), and (C) in Figure 10 correspond to dark-field images measured by inserting the objective aperture at positions 1, 2, and 3 in Figure 9, respectively. The white granular structure in Figure 10 indicates a crystalline phase, and it can be seen that nanocrystals with diameters of 2 to 8 nm are dispersed in the sample.

Claims

1. An alkali metal-containing oxide having a spinel structure and a composition represented by the following general formula (1): In an X-ray diffraction chart measured on the alkali metal-containing oxide at 25°C using CuKα radiation, a peak having a half-value width of 1.32 to 3.21° at 2θ is observed within a range of 43.9 to 44.4° at 2θ. A ｘ M’ ａ M’’ ｂ O ４ ・・・(1) (In formula (1), 1.2≦x≦2.0, 1.0≦a≦1.8, 0.1≦b≦0.5, and 1.1≦a+b<2.0, A is Li; M' is at least one element selected from the group consisting of Cr, Mn, and Ni; M″ is at least one selected from the group consisting of P and V.

2. The alkali metal-containing oxide according to claim 1 , wherein M″ contains V in the general formula (1).

3. An electrode comprising the alkali metal-containing oxide according to claim 1 or 2.

4. A battery comprising the electrode according to claim 3 as a positive electrode and a negative electrode containing lithium.

5. The alkali metal-containing oxide according to claim 1 or 2, which has an amorphous phase.

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