JP7809044B2 - Alkali metal-containing oxide, positive electrode active material, electrode and battery - Google Patents

Description

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

Secondary batteries are known in which alkali metal ions move between the positive and negative electrodes to charge and discharge. Lithium-ion secondary batteries are a typical example of such secondary batteries, and they are already in practical use as small power sources for devices such as mobile phones and laptops. Demand for them is growing because they can also be used as large-scale power sources for vehicles such as electric vehicles and hybrid vehicles, and as distributed power storage sources.

Alkali metal-containing oxides having a spinel-type crystal structure are known for use as positive electrodes for the secondary batteries. Such alkali metal-containing oxides, such as LiMn ₂ O ₄ , 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 (see Patent Documents 1 to 6).

Japanese Patent Application Publication No. 07-122299 Special Publication No. 2000-500280 Japanese Patent Application Laid-Open No. 2000-063123 Chinese Patent Application Publication No. 102163716 Chinese Patent Application Publication No. 103594700 Special table 2014-525667 publication

However, there was room for improvement in the charge/discharge capacity of spinel-type alkali metal-containing oxides.

The present invention has been made in consideration of the above circumstances, and aims to provide an alkali metal-containing oxide with excellent charge/discharge capacity, as well as an electrode and battery containing such an alkali metal oxide.

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 with CuKα radiation at 25°C, a peak having a half-value 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, and 0≦e<1.0,
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.

The alkali metal-containing oxide may be one in which x in general formula (1) is in the range of 2.2 to 2.8 when an electrochemical cell is prepared 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 battery is charged to 4.8 V on a Li/Li ⁺ basis and then discharged to 1.5 V.

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

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

In the above general formula (1), 1.1 < x ≦ 2.0 may be satisfied.

The electrode of the present invention contains the above-mentioned alkali metal-containing oxide.

The nonaqueous secondary battery of the present invention comprises the above electrode as a positive electrode and a negative electrode containing lithium.

The present invention has been made in consideration of the above circumstances, and aims to provide an alkali metal-containing oxide that has excellent charge/discharge capacity and coulombic efficiency, as well as an electrode and battery that contain such an alkali metal oxide.

FIG. 1 is an X-ray diffraction chart of the lithium-containing oxides of Examples 1 to 4. FIG. 2 is an X-ray diffraction chart of the lithium-containing oxides of Examples 5 to 8. FIG. 3 is an X-ray diffraction chart of the lithium-containing oxides of Examples 9 and 10 and Comparative Examples 1 to 3. 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. 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 Li _x Mn _1.4 V _0.3 O ₄ ) when the amount of oxygen in the composition of the alkali metal-containing oxide serving as the positive electrode active material is 4, and the vertical axis representing the battery voltage. FIG. 9 is a diagram showing an electron beam diffraction image of the sample of Example 5. FIG. 10 is a diagram showing a dark-field observation image of the sample of Example 5 observed by a transmission electron microscope.

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 using CuKα radiation at 25°C, a peak having a half-value 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, and 0≦e<1.0,
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.

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

Of the total amount of alkali metals contained in the alkali metal-containing oxide of this embodiment, the content of one type of 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. It may also contain substantially only one type of alkali metal (i.e., the content of alkali metals other than the one type of alkali metal is substantially 0 mol%). The one type of 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 primarily contains Li (for example, when the content of one type of 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 degrees in 2θ tends to be observed in the X-ray diffraction chart within a range of 43 to 45 degrees in 2θ.

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.

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.

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.

a may be between 0.9 and 1.9, or between 1.0 and 1.85. b may be between 0.06 and 0.58, or between 0.08 and 0.55, or between 0.1 and 0.5.

a + b may be between 1.2 and 1.95, or between 1.5 and 1.93.

Z is an element from Groups 2 to 16 of the periodic table other than oxygen, M', and M'', such as Al, Mg, Ca, Zr, Nb, Mo, Ru, W, and Sn.

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

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, or may contain F.

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.

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°.

The alkali metal-containing oxide of this embodiment may exhibit a peak in the X-ray diffraction chart described above within the 2θ range of 63 to 66°, with a half-width at 2θ of 0.5 to 8°. The half-width of this peak may be 1.0 to 7.5°.

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 an 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. The amorphous phase can be confirmed by observation using a transmission electron microscope (TEM).

The alkali metal-containing oxide of this embodiment may contain 8 to 15 mass% Li, 32 to 57 mass% 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% 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 may be observed, and a peak with a half-width of 0.5 to 5° may be observed within a 2θ range of 40 to 45°. The lithium-containing oxide may also contain oxygen, an element Z from Groups 2 to 16 of the periodic table other than M' and M". Specific examples of element Z include those exemplified as Z in general formula (1) above. The content of Z may be 20% by mass or less, 10% by mass or less, 5% by mass or less, 1% by mass or less, or substantially 0% by mass, relative to the total amount of the alkali metal-containing oxide. The alkali metal-containing oxide may also contain a halogen element, such as those exemplified as X in general formula (1) above. The content of the halogen element may be 20% by mass or less, 10% by mass or less, 5% by mass or less, 1% by mass or less, or substantially 0% by 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 both a crystalline phase (crystallites) and an amorphous phase.

The method for producing the alkali metal-containing oxide is not particularly limited, and examples thereof include a method of mechanochemically mixing a spinel-type oxide containing Li and M' with a lithium salt containing M _" in a ball mill _. Examples of spinel-type oxides include _LiMnTiO4 , _LiCrMnO4 , _LiMn2O4 , _{LiFeMnO4 , LiCoMnO4} , _{LiNi0.5Mn1.5O4 , and LiCu0.5Mn1.5O4 . Examples} of _lithium salts include _Li3VO4 , _{Li4SiO4 , Li2SiO3 , Li3P0.5V0.5O4 , Li2GeO4 , and Li2SO4 .} In addition, alkali metal oxides such as Li ₂ O, and oxides of M' or M'' such as V ₂ O ₅ , GeO ₂ , and SiO ₂ can also be used as raw materials. The raw materials are not limited to the above, and a compound containing at least one of Li, M', and M'' and oxygen can be blended to achieve the desired composition. The conditions for the ball mill are not particularly limited, and the rotation speed can be 100 to 700 rpm, and the mixing time can be 0.5 to 72 hours, or 10 to 60 hours. The mixing time can be 20 to 72 hours, or 30 to 60 hours. When X in general formula (1) is introduced, an alkali metal salt of X can also be used as a raw material.

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.

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

The positive electrode of this embodiment includes a current collector and a positive electrode mixture supported on the current collector. The positive electrode mixture may form a positive electrode mixture layer on the current collector.

The positive electrode mixture contains the lithium-containing oxide, and may also contain a conductive material (conductive additive), binder, etc. as needed. In other words, the lithium oxide may be contained in the positive electrode active material.

Conductive materials include carbon materials such as natural graphite, artificial graphite, cokes, carbon black, and acetylene black. Binders include thermoplastic resins, specifically fluororesins such as polyvinylidene fluoride (hereinafter also referred to as "PVDF"), polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers; and polyolefin resins such as polyethylene and polypropylene. Current collectors can be made of Al, Ni, stainless steel, etc.

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 it to the current collector, drying, and then pressing to adhere it to the collector. When forming a paste, for example, a slurry is prepared from the positive electrode active material, conductive material, binder, and organic solvent. 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.

The negative electrode of the battery is not particularly limited and may contain a negative electrode active material and, as necessary, a conductive additive, 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, as well as alloys or composites containing these elements, carbon materials such as graphite, and materials in which lithium ions are inserted between the layers of such carbon materials. For the negative electrode of a sodium-ion battery, materials in which the Li in the materials listed as negative electrode materials for lithium-ion batteries is replaced with Na can be used as the negative electrode material.

The electrolyte for 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. The electrolyte may also be a solid electrolyte. Examples of alkali metal salts include iodide salts, tetrafluoroborate salts, hexafluorophosphate salts, bis(fluorosulfonyl)imide salts, and bis(trifluoromethylsulfonyl)imide salts.

The organic solvent contained in the electrolyte solution is not particularly limited, but examples 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. Solvents may be used alone or in combination of two or more.

The alkali metal-containing oxide of this embodiment has excellent alkali metal ion occlusion ability. Therefore, the alkali metal-containing oxide of this embodiment may be such that, when an electrochemical cell is prepared including an electrode containing the alkali metal-containing oxide, a lithium metal counter electrode, and an electrolyte containing a lithium salt disposed between the electrode and the counter electrode, and the battery is charged to 4.8 V (initial charge) based on a Li/Li ⁺ standard and then discharged to 1.5 V, x in general formula (1) is 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.

The positive electrode active material of this embodiment includes a composite oxide containing an alkali metal element, element M', and element M", and contains 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 may be observed, and a peak with a half-width of 0.5 to 5° may be 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.

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):
In an X-ray diffraction chart of the alkali metal-containing oxide measured at 25°C using CuKα radiation, a peak having a half-value width of 0.5 to 5° in 2θ within a range of 40 to 45° in 2θ is observed.
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, and 0≦e<1.0,
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 of embodiment 1, wherein when an electrochemical cell is prepared 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 electrochemical cell is charged to 4.8 V on a Li/Li ⁺ basis and then discharged to 1.5 V, x in the general formula (1) is in the range of 2.2 to 2.8.
Embodiment 3
3. The alkali metal-containing oxide according to embodiment 1 or 2, wherein, in the general formula (1), A contains Li.
Embodiment 4
4. The alkali metal-containing oxide according to any one of embodiments 1 to 3, wherein in general formula (1), M″ comprises V.
Embodiment 5
5. The alkali metal-containing oxide according to any one of embodiments 1 to 4, wherein, in the general formula (1), 1.1<x≦2.0.
Embodiment 6
6. The alkali metal-containing oxide of any one of embodiments 1 to 5, having an amorphous phase.
Embodiment 7
An electrode comprising the alkali metal-containing oxide of any one of embodiments 1 to 6.
Embodiment 8
A battery comprising the electrode of embodiment 7 as a positive electrode and a negative electrode containing lithium.
Embodiment 9
A positive electrode active material comprising 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 an element M' which is at least one type selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, and Cu, and 3 to 30 mass % of an element M'' which is at least one type selected from the group consisting of Si, P, S, Ge, and V, wherein 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 having a half width of 0.5 to 5° is observed 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):
In an X-ray diffraction chart measured on the alkali metal-containing oxide at 25°C using CuKα radiation, a peak having a half-width at 2θ of 0.5 to 5° is observed within a range of 2θ of 40 to 45°.
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, and 0≦e<1.0,
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 1
The raw materials LiMn ₂ O ₄ powder and Li ₃ VO ₄ powder were produced as follows.
First, lithium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and manganese (IV) oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) 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 (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and vanadium (V) oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were mixed in a molar ratio of 3: ₁ and calcined in air at 650°C for 12 hours to obtain _Li3VO4 powder.

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 (PM200, manufactured by Retsch) and ball milled at a rotation speed of 500 rpm for 48 hours to obtain a lithium-containing oxide.

(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 LiMn ₂ O ₄ powder and Li ₃ VO ₄ powder and/or the mixing time were changed.

Example 7
A lithium-containing oxide was produced in the same manner as in Example 1, except that LiNi _0.5 Mn _1.5 O ₄ powder and Li ₃ VO ₄ powder were used in a molar ratio of 0.8:0.2 as raw materials.
The _{LiNi0.5Mn1.5O4 powder} was obtained 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 together with ethanol and 8 mm diameter zirconia balls in a wet ball mill, filtering, drying, and then firing the mixed powder in air at 600°C for 15 hours.

(Example 8)
A lithium-containing oxide was produced in the same manner as in Example 1, except that LiMn ₂ O ₄ powder and Li ₃ V _0.5 P _0.5 O ₄ powder were used as raw materials in a molar ratio of 0.8:0.2.
The _{Li3V0.5P0.5O4 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.

(Examples 9 and 10)
A lithium-containing oxide was produced in the same manner as in Example 1, except that LiCrMnO ₄ powder and Li ₃ VO ₄ 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.

(Comparative Example 1)
A lithium-containing oxide was produced in the same manner as in Example 1, except that only the LiMn ₂ O ₄ powder was subjected to ball milling.

(Comparative Example 2)
The raw material LiMn ₂ O ₄ powder produced in Example 1 was used as is.

<X-ray diffraction>
Powder X-ray diffraction measurements were performed on each of the lithium-containing oxides in the Examples and Comparative Examples using a powder X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation). Measurements were performed at room temperature (25°C). The lithium-containing oxide was filled into a cavity in a glass plate, and the glass plate on which the sample was placed was sealed in an airtight sample stage equipped with a beryllium window to protect it from air and moisture. Measurements were performed without exposure to the atmosphere. Using a CuKα radiation source at an output of 40 kV and 40 mA, measurements were performed over a diffraction angle range of 2θ = 10° to 90° at 0.02° increments and at a rate of 2°/min. The peak positions and half-widths of peaks observed in the 40 to 45° (2θ) range are shown in Tables 1 and 2. Figure 1 shows X-ray diffraction charts for the lithium-containing oxides of Examples 1 to 4. Figure 2 shows X-ray diffraction charts for the lithium-containing oxides of Examples 5 to 8. Figure 3 shows X-ray diffraction charts for the lithium-containing oxides of Examples 9 and 10 and Comparative Examples 1 to 3. As can be seen from FIGS. 1 to 3, the lithium-containing oxides of Examples 1 to 10 exhibited diffraction patterns similar to those of Comparative Example 2.

<Charge/discharge test>
(1) Preparation of 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 Fluoro Products Co., Ltd.) as a binder were weighed out so as to have a composition of positive electrode active material: conductive material: binder = 70:20:10 (mass ratio). 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 stretched into a circle on the mortar. The stretched mixture was pressed onto a 110 μm thick aluminum mesh (100 mesh, manufactured by Nilaco Corporation) as a current collector to obtain a positive electrode containing the positive electrode active material.
For Comparative Example 2, lithium-containing oxide (cathode active material), acetylene black (product name: HS-100, manufactured by Denka Co., Ltd.), and an N-methyl-2-pyrrolidone (NMP) solution of PVDF as a binder (KF Polymer, product number: L#1120, manufactured by Kureha Corporation) were added and kneaded in a ratio of 85:10:5 (mass ratio) of cathode active material: acetylene black: PVDF to prepare a paste-like cathode composite. When preparing the cathode composite, the viscosity of the paste was adjusted by adding NMP. The obtained cathode composite was applied to a 40 μm thick Al foil that served as a current collector and dried in the air at 60 ° C. for 1 hour, then vacuum dried at 150 ° C. for 8 hours, and punched into a circle with a diameter of 14.5 mm to obtain a cathode.

(2) Preparation and Evaluation of Li Half-Cells A coin-type battery CR2032 type was assembled using the above-mentioned positive electrode, a polyethylene porous film (16 μm thick) as a separator, a 1 M _LiPF6 solution as a non-aqueous 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, cutoff condition 6 mA/g.
Discharge conditions: constant current (CC) discharge was performed at 30 mA/g.

FIG. 4 is a graph showing the initial charge-discharge curves of Comparative Example 1 and Examples 1, 3, and 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 represents the capacity of the positive electrode active material, and the vertical axis represents 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 representing the lithium composition ratio x (i.e., x in the composition formula Li _x Mn _1.4 V _0.3 O ₄ ) when the amount of oxygen in the composition of the alkali metal-containing oxide serving as the positive electrode active material is 4, and the vertical axis representing the battery voltage. A in FIG. 8 indicates 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 _0.3 O ₄ . Thereafter, the charge-discharge test was carried out, and the composition of the lithium-containing oxide when _the state reached B in FIG. ₈ (when discharge was completed) was calculated from the current value to determine the amount of lithium ions _moved , which was _{Li2.45Mn1.4V0.3O4} , indicating that the lithium-ion absorption capacity was excellent.

<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: Acceleration voltage 200 kV
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 diffraction image of the sample of Example 5. The circle indicated by BF in the figure indicates 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 (5)

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. The alkali metal-containing oxide according to claim 1 , wherein M″ contains V in the general formula (1). An electrode comprising the alkali metal-containing oxide according to claim 1 or 2. A battery comprising the electrode according to claim 3 as a positive electrode and a negative electrode containing lithium. The alkali metal-containing oxide according to claim 1 or 2, which has an amorphous phase.