JP7557191B2 - Monoclinic lithium nickel manganese composite oxide and its manufacturing method - Google Patents

Description

Patent Act Article 30 Paragraph 2 applies (Part 1) Date posted on the website November 6, 2019 Website address http://www.denchi60.org/index.html http://www.denchi60.org/09.html https://confit-sfs.atlas.jp/customer/denchi60/redirect.html (Part 2) Date held November 13, 2019 to November 15, 2019 Name of the meeting The 60th Battery Symposium Venue Kyoto International Conference Center (Takaragaike, Sakyo Ward, Kyoto City)

The present invention relates to a monoclinic lithium nickel manganese composite oxide and a method for producing the same.

Lithium-ion secondary batteries are useful as secondary batteries for use in laptops, smartphones, etc. They are also considered important as batteries for electric vehicles and plug-in hybrid vehicles, and as system power sources for power load leveling systems, etc., and their development is underway.

Lithium-ion secondary batteries generally consist of a lithium transition metal composite oxide as the positive electrode, a carbon material as the negative electrode, and an organic electrolyte. The positive electrode active material functions as a lithium supply source, and is one of the most important components because the product of the amount of lithium ions desorbed and inserted in the positive electrode active material and the amount of positive electrode in the cell determines the battery capacity of the cell, and the operating voltage of the positive electrode active material determines the cell voltage.

Currently, lithium nickel manganese cobalt oxide (NMC) positive electrode active material and lithium nickel oxide positive electrode active material are commonly used as positive electrode active materials for large-capacity lithium-nickel oxide positive electrodes. Compared to NMC positive electrode active materials, lithium nickel oxide positive electrodes have a larger capacity per weight of positive electrode active material, but there are safety issues during charging. Therefore, NMC positive electrodes are used for large-capacity prismatic batteries, while lithium nickel oxide positive electrode active materials are only used for small-capacity cylindrical batteries.

Both types of positive electrode active materials contain the element cobalt, which is highly unevenly distributed and rare as a resource. To reduce the risk of instability and rising prices of cobalt raw materials, there is a strong demand for the development of cobalt-free positive electrode active materials with excellent charge and discharge characteristics.

The present inventors have revealed that lithium iron manganese composite oxides (Patent Document 1) and lithium nickel manganese composite oxides (Non-Patent Documents 1 and 2) having a monoclinic Li ₂ MnO ₃ layered rock salt structure exhibit excellent charge and discharge characteristics. However, it remains unclear which material should be selected from among the lithium nickel manganese composite oxides in order to manufacture a secondary battery that is excellent in particular in operating voltage, initial charge and discharge capacity and after charge and discharge cycles, and discharge rate characteristics.

JP 2009-179501 A

Mitsuharu Tabuchi et al., Electrochimica Acta, 210 (2016) 105-110. Mitsuharu Tabuchi et al., 59th Battery Symposium Abstracts 3D21, (2018)

In view of the above circumstances, the object of the present invention is to provide an electrode active material that has operating voltage, initial charge/discharge capacity and charge/discharge capacity after charge/discharge cycles, and discharge rate characteristics equivalent to or superior to those of existing NMC-based positive electrode active materials.

As a result of intensive research conducted by the inventors to achieve the above object, it was discovered that the above problem can be solved by setting the distribution or amount of transition metal ions consisting of Ni and Mn in a lithium nickel manganese composite oxide under specified conditions. Based on this knowledge, the inventors conducted further research and completed the present invention.

That is, the present invention includes the following lithium nickel manganese composite oxide and its manufacturing method.

Item 1. General formula (1):
Li _1+x (Ni _y Mn _1-y ) _1-x O ₂ (1)
[In the formula, x and y respectively represent 0<x<1/3 and 0.190≦y≦0.325.]
The present invention relates to a lithium nickel manganese composite oxide having a monoclinic Li ₂ MnO ₃ type layered rock salt structure, and the following (1) to (3):
(1) In the X-ray diffraction pattern of the crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the peak height of the (020) plane is smaller than that of the (20-2) plane and the (131) plane. The ratio of the peak to the peak height is 15.0% or less when y is 0.190 or more and less than 0.225, and is 8.7% or less when y is 0.225 or more and less than 0.275. , when y is 0.275 to 0.325, it is 5.0% or less;
(2) The sum (g _total ) of the average amount of transition metal present in the Li layer and the transition metal-Li layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure is 0.190 or more, and When y is less than 0.225, it is 0.720 or more, and when y is 0.225 to 0.325, it is 0.790 or more, and (3) the monoclinic Li ₂ MnO ₃ type layered rock salt structure In the hexagonal mesh structure of the transition metal-containing layer in the hexagonal mesh structure, the transition metal occupation rate (g _4g ) at the hexagonal mesh structure position (position 4g ) is calculated based on the transition metal occupation rate (g The lithium nickel manganese based composite oxide is characterized in that the value (g _4g -g _2b ) obtained by subtracting g 4g -g _2b ) is -0.10 to 0.20.

Item 2. The lithium nickel manganese composite oxide according to item 1, which satisfies (1) above.

Item 3. The lithium nickel manganese composite oxide according to Item 2, wherein the sum (g _total ) of the average abundance of the transition metal in the Li layer and the transition metal-Li layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure is 0.720 or more when the y is 0.190 or more and less than 0.225, and is 0.790 or more when the y is 0.225 to 0.325.

Item 4. The lithium nickel manganese composite oxide according to item 1, which satisfies (2) above.

Item 5. The lithium nickel manganese composite oxide according to any one of Items 2 to 4, wherein in a hexagonal mesh-ordered structure in a transition metal-containing layer in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, a value (g _4g -g _2b ) obtained by subtracting the transition metal occupancy (g _2b ) at a central position (position 2b ) of the hexagonal mesh-ordered structure from the transition metal occupancy (g _4g ) at a position constituting the hexagonal mesh-ordered structure (position 4g ) is -0.10 to 0.20.

Item 6. The lithium nickel manganese composite oxide according to item 1, which satisfies (3).

Item 7. The lithium nickel manganese composite oxide according to item 6, wherein y is 0.225 to 0.325.

Item 8. The lithium nickel manganese composite oxide according to any one of Items 1 to _{7, which is composed of a crystal phase of the monoclinic Li 2 MnO 3} type layered rock salt structure, or a mixed phase of a crystal phase of the monoclinic Li 2 MnO ₃ type layered rock salt structure and a crystal phase of a cubic rock salt structure.

Item 9. An electrode active material for a lithium ion secondary battery, comprising the lithium nickel manganese composite oxide according to any one of items 1 to 8.

Item 10. A lithium ion secondary battery comprising the electrode active material for lithium ion secondary batteries described in Item 9.

Item 11. A method for producing the lithium nickel manganese composite oxide according to any one of items 1 to 8,
1. A step of forming a precipitate by treating a manganese compound and a nickel compound with an alkali;
Step 2: oxidizing the precipitate to obtain a composite oxide precursor;
A step 3 of heat-treating the composite oxide precursor in an oxidizing atmosphere in the presence of a lithium compound, and a step 4 of heat-treating the product obtained in the step 3 in an inert atmosphere at a higher temperature than in the step 3.
The manufacturing method according to claim 1,

Item 12. The method according to item 11, further comprising step 5 of heat treating the product obtained in step 4 under a reducing atmosphere at a lower temperature than in step 4.

The present invention can provide an electrode material that has operating voltage, initial and post-charge/discharge capacity, and discharge rate characteristics equivalent to or superior to existing NMC-based positive electrode active materials.

(a) bc plane arrangement diagram of the crystal structure of the lithium nickel manganese based composite oxide of the present invention, (b) arrangement diagram within the transition metal layer on the ab plane of the crystal structure of the lithium nickel manganese based composite oxide of the present invention. 1 is a measured (+) and calculated (solid line) X-ray diffraction diagram of the lithium nickel manganese based composite oxide of Example 1 using CuKα radiation. Measured (+) and calculated (solid line) X-ray diffraction patterns of the lithium nickel manganese composite oxide of Example 2 using CuKα radiation. 1 is a measured (+) and calculated (solid line) X-ray diffraction diagram of the lithium nickel manganese based composite oxide of Comparative Example 1 using CuKα radiation. 5 shows the charge/discharge characteristics of a lithium ion secondary battery using the composite oxide of Example 1 as a positive electrode active material. Charging and discharging characteristics of a lithium ion secondary battery using the composite oxide of Example 2 as a positive electrode active material. Charging and discharging characteristics of a lithium ion secondary battery using the composite oxide of Comparative Example 1 as a positive electrode active material. 3 shows the discharge rate characteristics of a lithium ion secondary battery using the composite oxide of Example 1 as a positive electrode active material. 4 shows the discharge rate characteristics of a lithium ion secondary battery using the composite oxide of Example 2 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium ion secondary battery using the composite oxide of Comparative Example 1 as a positive electrode active material. 1 is a measured (+) and calculated (solid line) X-ray diffraction diagram of the lithium nickel manganese based composite oxide of Example 3 using CuKα radiation. 1 is a measured (+) and calculated (solid line) X-ray diffraction diagram of the lithium nickel manganese based composite oxide of Example 4 using CuKα radiation. Measured (+) and calculated (solid line) X-ray diffraction patterns of the lithium nickel manganese-based composite oxide of Comparative Example 2 using CuKα radiation. 5 shows the charge/discharge characteristics of a lithium ion secondary battery using the composite oxide of Example 3 as a positive electrode active material. 5 shows the charge/discharge characteristics of a lithium ion secondary battery using the composite oxide of Example 4 as a positive electrode active material. Charging and discharging characteristics of a lithium ion secondary battery using the composite oxide of Comparative Example 2 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium ion secondary battery using the composite oxide of Example 3 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium ion secondary battery using the composite oxide of Example 4 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium ion secondary battery using the composite oxide of Comparative Example 2 as a positive electrode active material.

In this specification, "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist of." In addition, in this specification, when a numerical range is indicated as "A to B," it means A or more and B or less.

(1. Lithium Nickel Manganese Composite Oxide)
The lithium nickel manganese based composite oxide of the present invention has the following general formula (1):
Li _1+x (Ni _y Mn _1-y ) _1-x O ₂ (1)
[In the formula, x and y respectively represent 0<x<1/3 and 0.190≦y≦0.325.]
It is expressed as:

The lithium nickel manganese based composite oxide of the present invention is a lithium nickel manganese based composite oxide having a monoclinic Li ₂ MnO ₃ type layered rock salt structure.

The monoclinic Li ₂ MnO ₃ type layered rock salt structure has a crystal structure of a space group represented by the following space formula (a) described in P. Strobel et al., J. Solid State Chem., 75, 90-98, (1988).

In the first aspect (requirement (3)) of the lithium nickel manganese based composite oxide of the present invention, in the hexagonal mesh structure in the transition metal-containing layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the value (g _4g -g _2b ) obtained by subtracting the transition metal occupancy (g _{2b ) at the center position of the hexagonal mesh structure from the transition metal occupancy (g 4g )} at the hexagonal mesh structure position is -0.10 or more and 0.17 or less. In the lithium nickel manganese based composite oxide of the present invention in this first aspect, as shown in FIG. 1, the transition metal (TM) ions consisting of Ni and Mn have a distribution different from that of the known Li ₂ MnO ₃ .

Figure 1(a) shows the entire layered rock-salt structure, and Figure 1(b) shows the cation arrangement in the TM-Li layer obtained by rotating the TM-Li layer in Figure 1(a) by 90 degrees. In Figure 1(a), the transition metal layers and lithium layers are alternately stacked with oxide ion (large gray circles) layers in between, which is similar to the hexagonal layered rock-salt crystal structure (space group represented by the spatial formula in (b) below) of conventional NMC positive electrodes, etc., but the cation distribution in the lithium layer and transition metal layer differs from that of conventional positive electrodes.

In addition, in the hexagonal layered rock-salt crystal structure of conventional NMC positive electrodes, there is only one type of cation lattice position in the lithium layer and the transition metal layer, but in the monoclinic layered rock-salt crystal structure of the present invention in the first embodiment, there are two types of cation lattice positions in the lithium layer and the transition metal layer.

In the lithium layer in FIG. 1(a), the lattice positions correspond to the 2c and 4h positions, and in the TM-Li layer, the lattice positions correspond to the 4g and 2b positions, as shown in FIG. 1(b). The lithium nickel manganese composite oxide of the present invention in the first embodiment is characterized by the transition metal ion distribution in this transition metal layer.

As shown in Fig. 1(b), the 4g position corresponds to a hexagonal mesh lattice component position, and the _2b position corresponds to the center position of the hexagonal mesh lattice. In an ideal _Li2MnO3 structure, transition metal ions occupy only the 4g position and lithium ions occupy the 2b position, but in reality, both lattice positions can be occupied by transition metal ions.

In the first aspect of the present invention, the difference (g _4g -g _2b ) between the transition metal ion occupancy rate at the 4g position (g _4g ) and the transition metal ion occupancy rate at the 2b position (g _2b ) obtained by the X-ray Rietveld method is small. The value of (g _4g -g _2b ) is -0.10 to 0.20, and preferably 0 to 0.17. If (g _4g -g _2b ) is less than -0.10, a high-value Mn source is required, which narrows the options for the Mn source and is industrially disadvantageous. On the other hand, if (g _4g -g _2b ) is greater than 0.17, a sample with a predetermined initial charge/discharge capacity and high discharge rate characteristics after the charge/discharge cycle cannot be obtained.

In addition, in the monoclinic Li ₂ MnO ₃ type layered rock salt structure, transition metals are present at the 2c and 4h positions in the Li layer, and transition metals are present at the 4g and 2b positions in the transition metal-Li layer as described above. The amount of transition metal per composition formula (g _total ) is defined as the sum of the average transition metal amount in the Li layer ((2g _4h + g _2c )/3) and the average transition metal amount in the transition metal-Li layer ((2g _4g + g _2b )/3). It is also important to increase this value as much as possible in order to improve the charge/discharge characteristics (especially the initial charge/discharge capacity and the discharge rate characteristics after the charge/discharge cycle). On the other hand, this value becomes smaller as the amount of Ni ions y per composition formula becomes smaller, so the optimal value differs depending on the y value. Specifically, in the lithium nickel manganese composite oxide of the present invention in the second aspect (requirement (2)), when the y value is 0.225 or more (0.225 to 0.325), the g _total value is 0.790 or more, preferably 0.795 to 0.900. On the other hand, when the y value is 0.190 or more and less than 0.225, the g _total value is 0.720 or more, preferably 0.725 to 0.800. If the g _total value is lower than the preferred range, it will be impossible to obtain a sample having the desired initial charge/discharge capacity and high discharge rate characteristics after the charge/discharge cycles.

In addition, the lithium nickel manganese composite oxide of the present invention preferably has as low an X-ray peak intensity ratio as possible, which is obtained by dividing the peak height of the (020) plane peak due to the hexagonal mesh structure seen near 2θ = 20° in the X-ray diffraction pattern using CuKα radiation by the height of a single peak consisting of the overlap of the (20-2) plane and the (131) plane peaks seen near 2θ = 45°. The ratio of this X-ray peak intensity tends to decrease as the y value increases, so the optimal value varies depending on the y value. Therefore, in the lithium nickel manganese composite oxide of the present invention in the third aspect (requirement (1)), when y is 0.190 or more and less than 0.225, the ratio of this X-ray peak intensity is 15.0% or less, preferably 11.0% or less. If the ratio exceeds 15.0%, a sample having the desired initial charge/discharge capacity and high discharge rate characteristics after charge/discharge cycles cannot be obtained. In addition, when y is 0.190 or more and less than 0.225, the lower limit of the ratio is not particularly limited, and is preferably 8.0%, for example. In addition, in the lithium nickel manganese composite oxide of the present invention in the third aspect (requirement (1)), when y is 0.225 or more and less than 0.275, the ratio of this X-ray peak intensity is 8.70% or less, preferably 8.40% or less. In this case, too, if the ratio exceeds 8.70%, a sample having the desired initial charge/discharge capacity and high discharge rate characteristics after charge/discharge cycles cannot be obtained. In addition, when y is 0.225 or more and less than 0.275, the lower limit of the ratio is not particularly limited, and is preferably 7.0%, for example. In addition, in the lithium nickel manganese composite oxide of the present invention in the third aspect (requirement (1)), when y is 0.275 to 0.325, the ratio of this X-ray peak intensity is 5.0% or less, preferably 4.7% or less. Again, if the ratio exceeds 5.0%, it will be impossible to obtain a material with the desired initial and post-charge/discharge capacity, as well as high discharge rate characteristics. Note that when y is 0.275 to 0.325, there is no particular limit to the lower limit of the ratio, and it is preferable to set it to, for example, 3.5%.

In addition, in general formula (1), x represents the amount of excess lithium, specifically, 0<x<1/3. If the value of x exceeds 1/3, lithium is not introduced into the structure and remains in the product as an impurity phase, and a large amount of lithium must be used, which is disadvantageous in terms of cost. In addition, x is preferably set to 0.05 to 0.30.

The lithium nickel manganese composite oxide of the present invention can be obtained by producing an oxide represented by a specific composition formula, for example, by using the coprecipitation-calcination method described below. It is believed that the adoption of this production method has the effect of reducing the difference (g _4g -g _2b ) between the transition metal ion occupancy rate at the 4g position (g _4g ) and the transition metal ion occupancy rate at the 2b position (g _2b ), the amount of transition metal per composition formula (g _total ), and the proportion of X-ray peak intensity.

For example, in the case of producing an oxide represented by a specific composition formula using the coprecipitation-calcination method described later, if the raw material composition is adjusted so that the y value is 0.225 to 0.325, a lithium nickel manganese-based composite oxide that satisfies all of the above requirements (1) to (3) is likely to be produced. Specifically, in a hexagonal mesh structure in a transition metal-containing layer in a monoclinic Li ₂ MnO ₃ type layered rock-salt structure, the value (g _4g -g _2b ) obtained by subtracting the transition metal occupancy (g _2b ) at the center position of the hexagonal mesh structure from the transition metal occupancy (g _4g ) at the hexagonal mesh structure position is -0.10 to 0.20 (requirement (3)), and in an X-ray diffraction pattern of a crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock-salt structure, the ratio of the peak height of the (020) plane to the peak heights of the (20-2) plane and the ( ₁₃₁ ) plane is 8.7% or less when y is 0.225 or more and less than 0.275, and is 5.0% or less when y is 0.275 to 0.325 (requirement (1)), and A lithium nickel manganese-based composite oxide in which the sum (g _total ) of the average abundance of the transition metal in the Li layer and the transition metal-Li layer in the type ₃ layered rock salt structure is 0.790 or more (requirement (2)) is likely to be produced.

On the other hand, for example, when an oxide represented by a specific composition formula is produced using the coprecipitation-calcination method described later, if the raw material composition is adjusted so that the y value is 0.190 or more and less than 0.225, a lithium nickel manganese-based composite oxide that satisfies the above-mentioned requirements (1) and (2) is likely to be produced. Specifically, in the X-ray diffraction pattern of the crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the ratio of the peak height of the (020) plane to the peak heights of the (20-2) plane and the (131) plane is 15.0% or less (requirement (1)), and the sum of the average abundances of the transition metals in the Li layer and the transition metal-Li layer in the _monoclinic Li ₂ MnO 3 type layered rock salt structure (g _total ) is 0.720 or more (requirement (2)).

Therefore, to stabilize the transition metal ion distribution, the amount of nickel ions per amount of pre-transition metal, y, is 0.190≦y≦0.325, and can also be 0.200≦y≦0.300. By setting y in this range, the transition metal ion distribution in the transition metal layer can be stabilized without making the amount of Mn in the composition formula too large, and the amount of Li ions in the composition formula is sufficient, resulting in improved charge/discharge capacity.

The lithium nickel manganese based composite oxide of the present invention is preferably composed of a crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure, or a mixed phase of the crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure and a crystal phase of a cubic rock salt structure.

In other words, the lithium nickel manganese composite oxide preferably contains a crystal phase of _the monoclinic _Li2MnO3 type layered rock salt structure described above. Of course, it is also preferable that the composite oxide is a mixed phase containing other rock salt crystal structures. Specifically, it is also preferable that the composite oxide is a mixed phase further containing a crystal phase of a cubic rock salt structure represented by the space group of the following formula (c).

The ratio of the monoclinic Li ₂ MnO ₃ type layered rock salt structure crystal phase to the cubic rock salt structure crystal phase is preferably in the range of about 100: 0 to 10: 90 (mass ratio) of monoclinic Li ₂ MnO ₃ type layered rock salt structure crystal phase:cubic rock salt structure crystal phase. The lithium nickel manganese composite oxide of the present invention may also contain other impurity phases (lithium carbonate, lithium hydroxide, manganese and nickel compounds, or composite compounds thereof, etc.) within a range that does not significantly affect the charge/discharge characteristics (about 0.01 to 10 mass%, assuming that the total amount of crystal phases that have peaks that can be confirmed in the X-ray diffraction pattern is 100 mass%). For example, when an oxide represented by a specific composition formula is produced using the coprecipitation-calcination method described later, a lithium nickel manganese-based composite oxide is likely to be produced in which the monoclinic Li ₂ MnO ₃ type layered rock salt structure single phase or the monoclinic Li ₂ MnO ₃ type layered rock salt structure is present in an extremely large proportion (for example, about 90 to 99.9 mass %, assuming that the total amount of crystal phases in which peaks can be confirmed in an X-ray diffraction pattern is 100 mass %).

(2. Electrode active material for lithium ion secondary battery and lithium ion secondary battery)
The lithium nickel manganese composite oxide of the present invention can be suitably used as an electrode active material for lithium ion secondary batteries, particularly as a positive electrode active material for lithium ion secondary batteries. It is also possible to manufacture a lithium ion secondary battery by a conventional method using the lithium manganese composite oxide of the present invention. Specifically, the lithium nickel manganese composite oxide of the present invention is used as a positive electrode active material, known metallic lithium, lithium titanate, silicon, silicon oxide, carbon-based materials (graphite-based materials, non-graphitic materials), etc. are used as a negative electrode active material, and a lithium ion secondary battery can be assembled according to a conventional method using an organic electrolyte solution in which lithium salts such as lithium perchlorate and LiPF ₆ are dissolved in a solvent such as known ethylene carbonate or dimethyl carbonate, or a polymer electrolyte, a sulfide solid electrolyte, and other known battery components.

(3. Method for producing lithium nickel manganese composite oxide)
The method for producing a lithium nickel manganese based composite oxide of the present invention includes, in this order, for example, step 1 of forming a precipitate by adjusting the alkalinity of a mixture of a manganese compound and a nickel compound, step 2 of oxidizing the precipitate to obtain a composite oxide precursor, step 3 of heating the composite oxide precursor together with a lithium compound in an oxidizing atmosphere, and step 4 of heating the product obtained in step 3 in an inert atmosphere at a temperature higher than that in step 3.

(3.1. Step 1)
In step 1, a manganese compound and a nickel compound are treated with an alkali to form a precipitate.

The manganese compound and nickel compound function as the manganese source and nickel source of the lithium nickel manganese composite oxide, respectively, and a wide variety of known manganese and nickel metal salts can be used, with no particular limitations. For example, in consideration of cost, it is preferable to use divalent salts (sulfates, nitrates, chlorides, acetates, and hydrates thereof, etc.). Potassium permanganate may also be used as a high-valence Mn source. In addition to these, it is also preferable to use, for example, manganese metal or nickel metal, or oxides of manganese or nickel, and it is also preferable to use manganese or nickel dissolved in acid as a metal salt. For both the manganese compound and the nickel compound, one of the above-mentioned substances may be used alone, or multiple types may be used in combination.

It is preferable that the mixing ratio of the manganese compound and nickel compound used is the same as the compounding ratio of manganese and nickel in the desired transition metal ion.

In particular, as described above, when the raw material composition is adjusted so that the y value in the lithium nickel manganese-based composite oxide of the present invention is 0.225 to 0.325 (nickel:manganese=0.225 to 0.325:0.675 to 0.775 (molar ratio)), a lithium nickel manganese-based composite oxide that satisfies all of the above requirements (1) to (3) is likely to be produced. Specifically, in a hexagonal mesh structure in a transition metal-containing layer in a monoclinic Li ₂ MnO ₃ type layered rock-salt structure, the value (g _4g -g _2b ) obtained by subtracting the transition metal occupancy (g _2b ) at the center position of the hexagonal mesh structure from the transition metal occupancy (g _4g ) at the hexagonal mesh structure position is -0.10 to 0.20 (requirement (1)), and in an X-ray diffraction pattern of a crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock-salt structure, the ratio of the peak height of the (020) plane to the peak heights of the (20-2) plane and the ( ₁₃₁ ) plane is 8.7% or less when y is 0.225 or more and less than 0.275, and is 5.0% or less when y is 0.275 to 0.325 (requirement (2)), and A lithium nickel manganese-based composite oxide in which the sum (g _total ) of the average abundance of the transition metal in the Li layer and the transition metal-Li layer in the type ₃ layered rock salt structure is 0.790 or more (requirement (3)) is likely to be produced.

On the other hand, as described above, when the raw material composition is adjusted so that the y value in the lithium nickel manganese-based composite oxide of the present invention is 0.190 or more and less than 0.225 (nickel:manganese=0.190 or more and less than 0.225: more than 0.775 and 0.800 or less (molar ratio)), a lithium nickel manganese-based composite oxide that satisfies the above requirements (2) to (3) is likely to be produced. Specifically, in the X-ray diffraction pattern of the crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock-salt structure, the ratio of the peak height of the (020) plane to the peak heights of the (20-2) plane and the (131) plane is 15.0% or less (requirement (2)), and the sum (g total ) of the average abundance of the transition metal in the Li layer and the transition metal-Li layer in the monoclinic Li ₂ MnO ₃ type _layered rock-salt structure is 0.720 or more (requirement (3)). A lithium nickel manganese-based composite oxide is easily produced.

From the above, appropriate selection can be made depending on the required physical properties and characteristics of the resulting lithium nickel manganese composite oxide of the present invention.

The manganese compound and the nickel compound are preferably a mixture containing the manganese compound and the nickel compound, more preferably a mixed solution of the manganese compound and the nickel compound dissolved in an appropriate solvent, and even more preferably a mixed aqueous solution of the manganese compound and the nickel compound dissolved in water. There are no particular limitations on the concentration of the mixed aqueous solution, and for example, the total concentration of the manganese compound and the nickel compound is preferably 0.01 to 5 mol/L, more preferably 0.1 to 2.0 mol/L.

A mixture of a manganese compound and a nickel compound is preferably made into a mixed liquid, more preferably a mixed aqueous solution, and is then treated with alkali to form a precipitate. The alkali treatment is achieved by making the mixture of a manganese compound and a nickel compound (mixed aqueous solution) alkaline.

The pH of the mixture of manganese compound and nickel compound to be treated with alkali should be set appropriately taking into consideration the type and concentration of the compounds. Specifically, the pH is preferably 8 or higher, and more preferably 11 or higher. There is no particular upper limit to the pH, but it is usually around 14.

There are no particular limitations on the specific method of operation for the alkaline treatment. For example, a method can be used in which a mixture of a manganese compound and a nickel compound is gradually added to an alkaline aqueous solution. When such a method is adopted, it is preferable to use, for example, a liquid delivery pump to drop the mixture (preferably a mixed liquid, more preferably a mixed aqueous solution) over a period of preferably 1 to 10 hours, more preferably 2 to 5 hours. By adopting such a method, a uniform precipitate can be obtained.

The alkaline substance used in the alkaline treatment is not particularly limited, and examples of the alkaline substances that can be used include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide, and ammonia. These alkaline substances are preferably dissolved in an appropriate solvent and used as an alkaline solution adjusted to a concentration of, for example, 0.1 to 20 mol/L, preferably 0.3 to 10 mol/L.

The solvent for dissolving the alkaline substance is not particularly limited, but in addition to water, it is also preferable to use a water-alcohol mixed solvent. The alcohol used here is preferably a water-soluble alcohol such as ethanol or methanol. By using a water-alcohol mixed solvent, precipitation can be easily performed at temperatures below 0°C, but it is more convenient to use water. In addition, by adding alcohol, it is also easy to generate a precipitation using potassium permanganate, which is one of the high-valence Mn sources.

The amount of alcohol used in the water-alcohol mixed solvent may be appropriately set according to the desired precipitation temperature. For example, it is preferable to use 10 to 50 parts by mass of alcohol per 100 parts by mass of water, and more preferably 20 to 40 parts by mass.

Considering that heat of neutralization is generated with the formation of precipitate, the set temperature during alkaline treatment is preferably -20 to 80°C, and more preferably -10 to 50°C.

(3.2. Step 2)
In step 2, the precipitate obtained in step 1 is oxidized to obtain a composite oxide precursor.

In step 2, it is preferable to perform an oxidation treatment on the reaction system containing the precipitate. The oxidation treatment can be carried out by blowing air or oxygen into the reaction system, preferably at a temperature of 0 to 150°C, more preferably 10 to 100°C, for preferably 1 to 7 days, more preferably 2 to 4 days.

The oxidation treatment is preferably carried out under wet conditions in order to obtain a uniform sample. A specific example of wet conditions is a bubbling treatment.

Through the above oxidation treatment, a complex oxide precursor can be obtained. The complex oxide precursor may be used as is in the next step 3, or it may be washed with distilled water or the like, and then the excess alkaline components and residual raw materials are removed, and the resulting purified complex oxide precursor is filtered off and then used in step 3.

(3.3. Step 3)
In step 3, the composite oxide precursor obtained in step 2 is heat-treated in an oxidizing atmosphere in the presence of a lithium compound.

The lithium compound to be used is not particularly limited, and for example, a lithium salt can be used. More specifically, examples include lithium carbonate, lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, and lithium acetate.

The amount of the lithium compound used relative to the molar amount of the transition metal compound is not particularly limited. However, it is preferable to use a value obtained by assuming yNiO-(1-y)Li ₂ MnO ₃ , where nickel is divalent and manganese is tetravalent, in (Li/(Ni+Mn) (molar ratio)). For example, when y is 0.250 as in Example 1 described later, from the above solid composition, (Li/(Ni+Mn) (molar ratio)) = 0.250 x 0 + 0.750 x 2 = 1.500
By using this, the water washing treatment after the heat treatment in step 4 described below becomes unnecessary, and the process can be simplified.

Although the composite oxide precursor and the lithium compound may be mixed and the resulting mixture subjected to heat treatment, it is preferable to form a slurry of the composite oxide precursor and the lithium compound in a solvent (preferably water), dry the slurry, and then subject the resulting dried product to heat treatment.

For example, when a water-soluble lithium compound is used, it is preferable to dissolve the lithium compound in water to prepare an aqueous solution, which is then mixed with the composite oxide precursor to form a slurry. On the other hand, when a water-insoluble lithium compound is used, it is preferable to disperse the lithium compound in water, add the composite oxide precursor, and mix to form a slurry.

The obtained slurry is preferably dried before heat treatment to obtain a dry mixture. There are no particular limitations on the drying conditions. For example, it is preferable to dry slowly at a temperature of 40 to 60°C.

Then, the mixture of the composite oxide precursor and the lithium compound, or the dried mixture obtained by drying the slurry, is subjected to heat treatment in an oxidizing atmosphere. Here, when the dried mixture is subjected to heat treatment, it is preferable to perform a pulverization treatment before the heat treatment. There are no particular limitations on the processing conditions for the pulverization treatment, and it is sufficient that the pulverized product does not contain coarse particles and has a uniform color tone.

In step 3, the heat treatment is carried out in an oxidizing atmosphere. Examples of the oxidizing atmosphere include air and oxygen.

The temperature conditions for the heat treatment are preferably 400 to 800°C, and more preferably 500 to 700°C. The heat treatment time is preferably, for example, 1 to 30 hours, and more preferably 3 to 20 hours.

(3.4. Step 4)
In step 4, the product obtained in step 3 is subjected to a heat treatment in an inert atmosphere at a higher temperature than in step 3.

The product obtained in step 3 may be used as is after the heat treatment in step 3, but it is preferable to pulverize it before use.

The heat treatment in step 4 is carried out in an inert atmosphere. There are no particular limitations on the inert atmosphere as long as it is an environment that suppresses oxidation at high temperatures, and examples of the inert atmosphere include an environment in nitrogen or argon.

The heat treatment temperature in step 4 is higher than the heat treatment temperature in step 3. If the heat treatment temperature in step 4 is lower than the heat treatment temperature in step 3, sufficient grain growth will not be obtained.

The specific temperature conditions for the heat treatment in step 4 are preferably 800 to 1000°C, and more preferably 850 to 950°C. The heat treatment time is preferably, for example, 1 to 30 hours, and more preferably 3 to 20 hours.

(3.5. Step 5)
In the method for producing a lithium nickel manganese based composite oxide of the present invention, it is also preferable to further provide a step 5 for carrying out a heat treatment. In the step 5, it is preferable to subject the product obtained in the step 4 to a heat treatment in a reducing atmosphere at a lower temperature than in the step 4. By providing the step 5, the charge/discharge capacity at the initial stage and after the charge/discharge cycles, and the discharge rate characteristics are further improved.

The product obtained in step 4 may be used as is after the heat treatment in step 4, but it is preferable to pulverize it before use.

The heat treatment in step 5 is preferably carried out in a reducing atmosphere. The reducing atmosphere is not particularly limited as long as it is an environment that reduces the sample, and an example of such an atmosphere is an environment of a hydrogen-nitrogen mixed gas. In the hydrogen-nitrogen mixed gas, the mixing ratio of hydrogen gas to nitrogen gas is not particularly limited, and from the viewpoint of the operating voltage, the initial charge-discharge capacity and the charge-discharge capacity after the charge-discharge cycle, and the discharge rate characteristics of the resulting lithium nickel manganese composite oxide of the present invention, the hydrogen gas can usually be 1 to 10% by volume (particularly 3 to 7% by volume) and the nitrogen gas can be 90 to 99% by volume (particularly 93 to 97% by volume).

The heat treatment temperature in step 5 is preferably lower than the heat treatment temperature in step 4. By setting the heat treatment temperature in step 5 lower than the heat treatment temperature in step 4, it is easier to suppress decomposition of the sample.

The specific temperature conditions for the heat treatment in step 5 are preferably 300 to 600°C, and more preferably 350 to 500°C. The heat treatment time is preferably, for example, 0.5 to 30 hours, and more preferably 1 to 20 hours.

Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and can of course be embodied in various forms without departing from the spirit of the present invention.

The following provides a more detailed explanation of the present invention based on examples, but the present invention is not limited to these.

Example 1
18.17 g of nickel (II) nitrate hexahydrate and 37.11 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Ni:Mn molar ratio = 25:75) were added to 500 mL of distilled water and completely dissolved to obtain a Ni-Mn aqueous solution (0.50 mol/L). A sodium hydroxide aqueous solution (a solution obtained by dissolving 50 g of sodium hydroxide in 500 mL of distilled water; 2.50 mol/L) was prepared in another beaker. This sodium hydroxide aqueous solution was placed in a titanium beaker and placed in a thermostatic bath while stirring, and the thermostatic bath was kept at +20°C. Next, the Ni-Mn aqueous solution was gradually added dropwise to this sodium hydroxide aqueous solution over 2 to 3 hours to form a Ni-Mn precipitate (step 1). After confirming that the reaction solution had become completely alkaline (pH 11 or higher), oxygen was blown into the reaction solution containing the coprecipitate at room temperature with stirring for 48 hours or more to carry out a wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. To the obtained material, 0.75 times the total amount of lithium carbonate (13.85 g; (Li/(Ni+Mn) (molar ratio) is 1.500)) and 200 mL of distilled water were added, and the mixture was mixed in a mixer to produce a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) petri dish and dried at 50°C for 2 days.

The dried powder was ground in a vibration mill, then placed in an electric furnace and subjected to primary firing in air at 650°C for 5 hours (step 3). The powder was then removed from the electric furnace, ground again in a vibration mill, then placed in an electric furnace and subjected to secondary firing in a nitrogen stream at 950°C for 5 hours (step 4). The powder was then removed from the electric furnace and ground again in a vibration mill to obtain a lithium nickel manganese composite oxide.

(Comparative Example 1)
The secondary firing in step 4 was carried out in the same manner as in Example 1, except that the inert nitrogen atmosphere was changed to air, to obtain a lithium nickel manganese composite oxide.

Example 2
21.81 g of nickel (II) nitrate hexahydrate and 34.63 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Ni:Mn molar ratio = 3:7) were added to 500 mL of distilled water and completely dissolved to obtain a Ni-Mn aqueous solution (0.50 mol/L). A sodium hydroxide aqueous solution (a solution obtained by dissolving 50 g of sodium hydroxide in 500 mL of distilled water; 2.50 mol/L) was prepared in another beaker. This sodium hydroxide aqueous solution was placed in a titanium beaker and placed in a thermostatic bath while stirring, and the thermostatic bath was kept at +20°C. Next, the Ni-Mn aqueous solution was gradually added dropwise to this sodium hydroxide aqueous solution over 2 to 3 hours to form a Ni-Mn precipitate (step 1). After confirming that the reaction solution had become completely alkaline (pH 11 or higher), oxygen was blown into the reaction solution containing the coprecipitate at room temperature with stirring for 48 hours or more to carry out a wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. The resulting material was mixed with 1.00 times the total amount of lithium carbonate (18.47 g; (Li/(Ni+Mn) (molar ratio) is 2.000)) and 200 mL of distilled water, mixed in a mixer to prepare a uniform slurry, then transferred to a polytetrafluoroethylene (PTFE) petri dish and dried at 50°C for 2 days. The dried powder was pulverized in a vibration mill, placed in an electric furnace, and subjected to primary firing in oxygen at 500°C for 20 hours (step 3). The powder was then removed from the electric furnace, pulverized again in a vibration mill, and placed in an electric furnace and subjected to secondary firing at 850°C for 5 hours in a nitrogen stream (step 4). The powder was then removed from the electric furnace, pulverized again in a vibration mill, and subjected to tertiary firing at 425°C for 1 hour in a 4% by volume hydrogen-96% by volume nitrogen mixed gas (step 5). The powder was then removed from the electric furnace, washed with distilled water, filtered, and dried to obtain a lithium nickel manganese composite oxide.

X-ray diffraction measurement (Example 1)
A comparison of the measured pattern (+) of Example 1 obtained using the X-ray Rietveld analysis software RIETAN-FP (Fujio Izumi et al., Solid State Phenom. 130 (2007) 15-20.) and the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell (solid line) is shown in FIG. 2 (peak positions are indicated by vertical bars, and the residual between the measured value and the calculated value is indicated near the intensity 0). It was confirmed that the difference between the measured value and the calculated value was small, and reliable analytical values were obtained. The obtained lattice constants were a = 4.9572(3) Å, b = 8.5825(3) Å, c = 5.03447(16) Å, β = 109.229(4) °, and V = 202.2(3) Å ³ . The occupancy rate of the transition metal (assuming virtual atom Ni _0.25 Mn _0.75 ) at each lattice site was calculated assuming that the isotropic thermal vibration parameter B was 1, and the results are shown in Table 1 below.

X-ray diffraction measurement (Example 2)
A comparison (solid line) between the measured pattern (+) of Example 2 obtained using the X-ray Rietveld analysis software RIETAN-FP and the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 3 (peak positions are indicated by vertical bars, and the residual between the measured value and the calculated value is indicated near the intensity 0). It was confirmed that the difference between the measured value and the calculated value was small, and reliable analytical values were obtained. The obtained lattice constants were a = 4.9587 (5) Å, b = 8.5750 (5) Å, c = 5.0232 (3) Å, β = 109.197 (8) °, and V = 201.7 (6) Å ^3. The transition metal (assuming a virtual atom Ni _0.3 Mn _0.7 ) occupancy rate at each lattice position was calculated assuming an isotropic thermal vibration parameter B of 1, as shown in Table 1 below.

X-ray diffraction measurement (Comparative Example 1)
A comparison (solid line) between the measured pattern (+) of Comparative Example 1 obtained using the X-ray Rietveld analysis software RIETAN-FP and the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 4 (the peak positions are indicated by vertical bars, and the residual between the measured value and the calculated value is indicated near the intensity 0). It was confirmed that the difference between the measured value and the calculated value was small, and reliable analytical values were obtained. The obtained lattice constants were a = 4.9565 (4) Å, b = 8.5704 (4) Å, c = 5.0316 (2) Å, β = 109.168 (6) °, and V = 201.9 (4) Å ^3. The transition metal (assuming virtual atom Ni _0.25 Mn _0.75 ) occupancy rate at each lattice position was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 1 below.

As shown in Table 1, the complex oxide of Example 1 has a difference g _4g -g _2b between the occupancy rate of the hexagonal network position (4g position) and the occupancy rate of the central position (2b position) of the hexagonal network, which is 0.090, and is clearly within the scope of the present invention. In addition, the ratio I _{020 /} I 20-2,131 of the peak height of the (020) plane peak near 2θ = 20 ° and the (20-2) plane and (131) plane _peak near _{2θ = 45 ° is 8.35%, which is clearly within the scope of the present invention. In addition, the transition metal amount (g total ) per composition formula defined by the sum of the average transition metal amount in the Li layer ((2g 4h} +g _2c ) / 3) and the average transition metal amount in the transition metal-Li layer ((2g _4g +g _2b ) / ₃ ) is 0.805, which is clearly within the scope of the present invention.

As shown in Table 1, the difference g _4g -g _2b between the occupancy rate of the hexagonal mesh position (4g position) and the occupancy rate of the central position (2b position) of the hexagonal mesh is 0.162 for the composite oxide of Example 2, which is clearly within the scope of the present invention. The ratio I 020 /I 20-2,131 of the peak height of the peak of the (020) plane near 2θ = 20 ° and the peak of the (20-2) plane and the ( ₁₃₁ ) plane near 2θ = ₄₅ ° is 4.46%, which is clearly within the scope of the present invention. The transition metal amount (g total ) per composition formula defined by the sum of the average transition metal amount in the Li layer ((2g _4h +g _2c ) / 3) and the average transition metal amount in the transition metal-Li layer ((2g _{4g +} g _2b ) / 3) is 0.797, which is clearly within the scope of the present invention.

In addition, as for the composite oxide of Comparative Example 1, as shown in Table 1, the difference g _4g -g _2b between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the central position (2b position) of the hexagonal network is 0.283, which is clearly outside the scope of the present invention. In addition, the ratio I ₀₂₀ /I _20-2,131 of the peak height of the (020) plane peak near 2θ = 20 ° and the (20-2) plane and (131) plane peak near _{2θ = 45 ° is 8.95%, which is clearly outside the scope of the present invention. In addition, the transition metal amount (g total ) per composition formula defined by the sum of the average transition metal amount in the Li layer ((2g 4h} +g _2c ) / 3) and the average transition metal amount in the transition metal-Li layer ((2g _{4g +} g _2b ) / 3) is 0.784, which is clearly outside the scope of the present invention. Therefore, it is understood that step 4 must be carried out in an inert atmosphere.

Chemical Analysis (Examples 1-2 and Comparative Example 1)
The transition metal content of the lithium nickel manganese composite oxides of Examples 1 and 2 and Comparative Example 1 was determined by a wavelength dispersive X-ray fluorescence spectrometer, and the lithium content was determined by ICP emission spectrometry, and the results are shown in Table 2 below. The x value in the table was calculated from Li/(Ni+Mn) (molar ratio) using the following formula:
x=(Li/(Ni+Mn)-1)/(Li/(Ni+Mn)+1)
On the other hand, the y value is Ni/(Ni+Mn) (molar ratio) itself. It is clear that both of the composite oxides of Examples 1 and 2 are within the composition formula range of the present invention.

Evaluation of charge/discharge characteristics (Examples 1 and 2 and Comparative Example 1)
20 mg of the lithium nickel manganese composite oxide of Examples 1-2 and Comparative Example 1 and 5 mg of acetylene black powder were thoroughly mixed in a mortar, and then 0.5 mg of polytetrafluoroethylene powder was added to bond them together. This was pressed onto an aluminum mesh to prepare a composite electrode. The composite electrode was vacuum dried overnight at 120°C, and then introduced into a glove box with a dew point of -80°C or less, and a coin-type lithium secondary battery was assembled using metallic lithium as the negative electrode and 1M LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio ethylene carbonate: dimethyl carbonate = 3:7) as the electrolyte. The prepared battery was taken out of the glove box and connected to a charge/discharge test device, and a charge/discharge test was performed at 30°C at the start of charging and at a current density of 40 mAh/g. A stepwise charging method was applied up to the fourth cycle for electrochemical activation. From the first to fourth cycles, the charge capacity was increased from 80 mAh/g by 40 mAh/g, and in each cycle, the battery was discharged to 2.0 V. In the fifth cycle, the battery was charged to 4.8 V and then discharged to 2.0 V. After that, from the sixth cycle onwards, the battery was charged and discharged at a constant current 29 times within the potential range of 2.0-4.6 V.

The charge and discharge characteristics of the lithium secondary batteries using Examples 1 and 2 and Comparative Example 1 as the positive electrodes are shown in Figures 5 to 7, respectively. In both Figures 5 to 7, the curves sloping upward to the right indicate the charge curves (indicated by the subscript c), and the curves sloping downward to the right indicate the discharge curves (indicated by the subscript d). The numbers indicate the number of cycles. Note that cycles 1 to 4 are not shown in the figures, as they are cycles for electrochemical activation. The charge and discharge capacities of Examples 1 and 2 and Comparative Example 1 are shown in Table 3 below.

From Figures 5, 7 and Table 3, it can be seen that the lithium ion secondary battery of Example 1 has a larger charge/discharge capacity from the 5th cycle to the 34th cycle and a smaller change in the charge/discharge curve over the cycles compared to the lithium ion secondary battery of Comparative Example 1. In addition, the average discharge voltages at the 5th cycle of the batteries of Examples 1 and 2 were 3.56 and 3.61 V, respectively, which were almost equal to or higher than the value (3.55 V) of the battery of Comparative Example 1.

From Figures 6, 7 and Table 3, it can be seen that the lithium ion secondary battery of Example 2 has a larger charge/discharge capacity from the 5th cycle to the 34th cycle and a smaller change in the charge/discharge curve over the cycles than the lithium ion secondary battery of Comparative Example 1, and also has a larger charge/discharge capacity from the 5th cycle to the 34th cycle and a smaller change in the charge/discharge curve over the cycles than the lithium ion secondary battery of Example 1. In addition, the average discharge voltage at the 5th cycle of the battery of Example 2 was 3.59 V.

Discharge rate characteristic evaluation (Examples 1 and 2 and Comparative Example 1)
Next, the discharge rate characteristics under high current density were evaluated using the lithium ion secondary batteries of Examples 1 and 2 and Comparative Example 1. The batteries were charged and discharged in the same manner as in the above cycle test until the fifth cycle, and then evaluated in a potential range of 2.0-4.6 V, with the current density during charging fixed at 40 mA/g and the discharge current density changed from 100 mA/g to 400 mA/g. Note that, since the charge depth of the battery after the high current density discharge test evaluation is significantly different from that of a normal constant current density test, one cycle of charge and discharge under low current density (40 mA/g) was performed after each high current density discharge test to adjust it.

Figures 8 to 10 and Table 4 show the discharge rate characteristics of the lithium secondary batteries of each example and comparative example.

From Figures 8 to 10 and Table 4, it is clear that the lithium ion secondary batteries of Examples 1 and 2 have larger discharge capacities at each current density and superior discharge rate characteristics compared to the lithium ion secondary battery of Comparative Example 1. Furthermore, the addition of step 5 improves both the charge/discharge characteristics and the discharge rate characteristics.

Example 3
14.59 g of nickel (II) nitrate hexahydrate and 31.61 g of potassium permanganate (VII) (total amount 0.25 mol, Ni:Mn molar ratio = 2:8) were added to 700 mL of distilled water and completely dissolved to obtain a Ni-Mn aqueous solution (0.36 mol/L). A sodium hydroxide aqueous solution (a solution obtained by dissolving 50 g of sodium hydroxide in 500 mL of distilled water and 200 mL of ethanol; 1.79 mol/L) was prepared in another beaker. This sodium hydroxide aqueous solution-ethanol mixed solution was placed in a titanium beaker and left to stand in a thermostatic bath while stirring, and the thermostatic bath was kept at +20°C. Next, the Ni-Mn aqueous solution was gradually dropped into this sodium hydroxide aqueous solution-ethanol mixed solution over 2 to 3 hours to form a Ni-Mn precipitate (step 1). After confirming that the reaction solution had become completely alkaline (pH 11 or higher), oxygen was blown into the reaction solution containing the coprecipitate at room temperature with stirring for 48 hours or more to carry out a wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. The resulting material was mixed with 1.00 times the molar ratio of lithium carbonate (18.47 g; (Li/(Ni+Mn) (molar ratio) was 2.00)) and 200 mL of distilled water, mixed in a mixer to prepare a uniform slurry, which was then transferred to a polytetrafluoroethylene (PTFE) petri dish and dried at 50°C for two days. The dried powder was pulverized in a vibration mill, placed in an electric furnace, and subjected to primary firing at 650°C in air for five hours (step 3). The powder was then removed from the electric furnace, pulverized again in a vibration mill, and placed in an electric furnace for secondary firing at 900°C for one hour in a nitrogen stream (step 4). The powder was then removed from the electric furnace, pulverized again in a vibration mill, and subjected to tertiary firing at 450°C for three hours in a 4% by volume hydrogen-96% by volume nitrogen mixed gas (step 5). The powder was then removed from the electric furnace, washed with distilled water, filtered, and dried to obtain a lithium nickel manganese composite oxide.

Example 4
A sample was prepared in the same manner as in Example 3 except that the tertiary firing was not performed, and a lithium nickel manganese based composite oxide was obtained.

(Comparative Example 2)
14.59 g of nickel (II) nitrate hexahydrate and 39.58 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Ni:Mn molar ratio = 2:8) were added to 500 mL of distilled water and completely dissolved to obtain a Ni-Mn aqueous solution (0.50 mol/L). A sodium hydroxide aqueous solution (a solution obtained by dissolving 50 g of sodium hydroxide in 500 mL of distilled water; 2.50 mol/L) was prepared in another beaker. This sodium hydroxide aqueous solution was placed in a titanium beaker and left to stand in a thermostatic bath while stirring, and the thermostatic bath was kept at +20°C. Next, the Ni-Mn aqueous solution was gradually added dropwise to this sodium hydroxide aqueous solution over 2 to 3 hours to form a Ni-Mn precipitate (step 1). After confirming that the reaction solution had become completely alkaline (pH 11 or higher), oxygen was blown into the reaction solution containing the coprecipitate at room temperature with stirring for 48 hours or more to carry out a wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. The resulting material was mixed with 1.00 times the molar ratio of lithium carbonate (18.47 g; (Li/(Ni+Mn) (molar ratio) is 2.00)) and 200 mL of distilled water, mixed in a mixer to prepare a uniform slurry, and then transferred to a polytetrafluoroethylene (PTFE) petri dish and dried at 50°C for 2 days. The dried powder was pulverized in a vibration mill, placed in an electric furnace, and subjected to primary firing at 650°C in air for 5 hours (step 3). The powder was then removed from the electric furnace, pulverized again in a vibration mill, and placed in an electric furnace for secondary firing at 900°C in air for 5 hours (step 4). The powder was then removed from the electric furnace, washed with distilled water, filtered, and dried to obtain a lithium nickel manganese composite oxide.

X-ray diffraction measurement (Example 3)
A comparison (solid line) between the measured pattern (+) of the lithium nickel manganese composite oxide of Example 3 and the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 11 (peak positions are indicated by vertical bars, and the residual between the measured value and the calculated value is indicated near the intensity 0). It can be seen that the difference between the measured value and the calculated value is small, and reliable analytical values were obtained. The obtained lattice constants were a = 4.9474 (3) Å, b = 8.5579 (4) Å, c = 5.0219 (2) Å, β = 109.232 (5) °, and V = 200.8 (4) Å ^3. The transition metal (assuming a virtual atom Ni _0.2 Mn _0.8 ) occupancy rate at each lattice position is shown in Table 5, as in Example 1. From Table 5, the difference g _4g -g _2b between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position) is 0.323. In addition, the peak height ratio I ₀₂₀ /I _20-2,131 of the peak of the (020) plane near 2θ = 20° to the peak of the (20-2) plane and the (131) plane near 2θ = 45° is 9.64%, which is clearly within the range of the present invention. In addition, the amount of transition metal per composition formula (g _total ) is 0.759, which is clearly within the range of the present invention.

X-ray diffraction measurement (Example 4)
A comparison (solid line) between the measured pattern (+) of the lithium nickel manganese composite oxide of Example 4 and the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 12 (the peak positions are indicated by vertical bars, and the residual between the measured value and the calculated value is indicated near the intensity 0). It can be seen that the difference between the measured value and the calculated value is small, and a reliable analytical value was obtained. The obtained lattice constants were a = 4.9435 (3) Å, b = 8.5529 (4) Å, c = 5.0198 (2) Å, β = 109.245 (5) °, and V = 200.4 (3) Å ^3. The transition metal (assuming a virtual atom Ni _0.2 Mn _0.8 ) occupancy rate at each lattice position is shown in Table 5, as in Example 1. From Table 5, the difference g _4g -g _2b between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position) is 0.321. In addition, the peak height ratio I ₀₂₀ /I _20-2,131 of the peak of the (020) plane near 2θ = 20° to the peak of the (20-2) plane and the (131) plane near 2θ = 45° is 10.6%, which is clearly within the range of the present invention. In addition, the amount of transition metal per composition formula (g _total ) is 0.746, which is clearly within the range of the present invention.

X-ray diffraction measurement (Comparative Example 2)
A comparison (solid line) between the measured pattern (+) of the lithium nickel manganese composite oxide of Comparative Example 2 and the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 13 (the peak positions are indicated by vertical bars, and the residual between the measured value and the calculated value is indicated near the intensity 0). It can be seen that the difference between the measured value and the calculated value is small, and a reliable analytical value was obtained. The obtained lattice constants were a = 4.93362 (19) Å, b = 8.5395 (2) Å, c = 5.02392 (14) Å, β = 109.284 (2) °, and V = 199.79 (16) Å ^3. The transition metal occupancy rate at each lattice position is shown in Table 5, as in Example 1. From Table 5, the difference g _4g -g _2b between the occupancy rate of the hexagonal mesh configuration position (4g position) and the occupancy rate of the hexagonal mesh center position (2b position) is 0.347. In addition, the peak height ratio I ₀₂₀ /I _20-2,131 of the peak of the (020) plane near 2θ=20° to the peak of the (20-2) plane and the (131) plane near 2θ=45° is 16.3%, which is clearly outside the range of the present invention. In addition, the amount of transition metal per composition formula (g _total ) is 0.704, which is clearly outside the range of the present invention. Therefore, it is understood that it is necessary to carry out step 4 under an inert atmosphere.

Chemical Analysis (Examples 3-4 and Comparative Example 2)
The transition metal amounts and lithium amounts of the lithium nickel manganese composite oxides of Examples 3 and 4 and Comparative Example 2 were determined by ICP emission spectrometry, and the results are shown in Table 6 below. The x value in the table was calculated from Li/(Ni+Mn) (molar ratio) using the following formula:
x=(Li/(Ni+Mn)-1)/(Li/(Ni+Mn)+1)
On the other hand, the y value is Ni/(Ni+Mn) (molar ratio) itself. It is clear that the composite oxides of Examples 3 and 4 are all within the range of the composition formula of the present invention.

Evaluation of charge/discharge characteristics (Examples 3 to 4 and Comparative Example 2)
The samples of Examples 3-4 and Comparative Example 2 were subjected to a charge-discharge test in the same manner as in Example 1. The charge-discharge characteristics of the lithium secondary batteries using the samples of Examples 3-4 and Comparative Example 2 as the positive electrodes are shown in Figures 14-16, respectively. In both Figures 14-16, the curves sloping upward to the right indicate the charge curves (indicated by the subscript c), and the curves sloping downward to the right indicate the discharge curves (indicated by the subscript d). The numbers indicate the number of cycles. Note that cycles 1-4 are not shown because they are cycles for electrochemical activation. The charge-discharge capacities of Examples 3-4 and Comparative Example 2 are shown in Table 7 below.

As can be seen from Figures 14 to 16 and Table 7, the samples of Examples 3 and 4 have a higher capacity than the sample of Comparative Example 2, and since they maintain a high capacity even after 34 charge/discharge cycles, it is clear that they have excellent charge/discharge characteristics.

Next, the discharge rate characteristics under high current density were evaluated using the lithium ion secondary batteries of Examples 3 and 4 and Comparative Example 2. The evaluation conditions were the same as those of Examples 1 and 2 and Comparative Example 1. The results are shown in Figures 17 to 19 and Table 8 below.

From Figures 17 to 19 and Table 8, it is clear that the samples of Examples 3 and 4 have better discharge rate characteristics than the sample of Comparative Example 2. Furthermore, adding step 5 improves both the charge/discharge characteristics and the discharge rate characteristics.

From the above, it is believed that the lithium nickel manganese composite oxide of the present invention has a unique transition metal ion distribution or abundance, and therefore has superior charge/discharge characteristics compared to those with a normal transition metal ion distribution and abundance, and can be suitably used as a positive electrode material for large lithium ion secondary batteries for vehicles, etc.

The lithium nickel manganese composite oxide of the present invention has operating voltage, initial charge/discharge capacity and charge/discharge capacity after charge/discharge cycles, and discharge rate characteristics that are equal to or better than those of existing NMC-based positive electrode materials. Therefore, it can be suitably used in batteries for electric vehicles or plug-in hybrid vehicles, or stationary storage batteries, etc.

Claims (12)

General formula (1):
Li _1+x (Ni _y Mn _1-y ) _1-x O ₂ (1)
[wherein x and y are 0<x< _1/3 and 0.190≦y≦0.325, respectively.] and is a lithium nickel manganese composite oxide having a monoclinic _Li2MnO3 type layered rock salt structure,
(2) The sum (g _total ) of the average abundance of the transition metal in the Li layer and the transition metal-Li layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure is 0.725 to 0.800 when the y is 0.190 or more and less than 0.225, and is 0.790 to 0.900 when the y is 0.225 to 0.325.
Lithium nickel manganese composite oxide. (1) In the X-ray diffraction pattern of the crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the ratio of the peak height of the (020) plane to the peak heights of the (20-2) plane and the (131) plane is 15.0% or less when y is 0.190 or more and less than 0.225, 8.7% or less when y is 0.225 or more and less than 0.275, and 5.0% or less when y is 0.275 to 0.325. The lithium nickel manganese composite oxide according to claim 1. (3) The lithium nickel manganese-based composite oxide according to claim 1 or 2, wherein in a hexagonal mesh-ordered structure in a transition metal-containing layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the value (g _4g -g _2b ) obtained by subtracting the transition metal occupancy (g _2b ) at the central position (2b position) of the hexagonal mesh-ordered structure from the transition metal occupancy (g _4g ) at the hexagonal mesh-ordered structure position (4g position) is -0.10 to 0.20. The lithium nickel manganese composite oxide according to claim 3, wherein y is 0.225 to 0.325. General formula (1):
Li _1+x (Ni _y Mn _1-y ) _1-x O ₂ (1)
[wherein x and y are 0<x<1/3 and 0.225≦y≦0.325, respectively.] and is a lithium nickel manganese composite oxide having a monoclinic Li ₂ MnO ₃ type layered rock salt structure,
(3) In the hexagonal mesh structure in the transition metal-containing layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the value (g _4g -g 2b ) obtained by subtracting the transition metal occupancy (g _2b ) at the central position (2b position) of the hexagonal mesh structure from the transition metal occupancy (g _4g ) at the hexagonal mesh structure position ( _{4g position} ) is -0.10 to 0.20.
Lithium nickel manganese composite oxide. (1) In the X-ray diffraction pattern of the crystal phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure, the ratio of the peak height of the (020) plane to the peak heights of the (20-2) plane and the (131) plane is 8.7% or less when y is 0.225 or more and less than 0.275, and is 5.0% or less when y is 0.275 to 0.325. The lithium nickel manganese composite oxide according to claim 5. (2) The lithium nickel manganese composite oxide according to claim 5 or 6, wherein the sum (g _total ) of the average abundance of the transition metal in the Li layer and the transition metal-Li layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure is 0.790 or more. The lithium nickel manganese composite oxide according to any one of claims ₁ to _{7, which is composed of a crystal phase of the monoclinic Li 2 MnO 3} type layered rock salt structure, or a mixed phase of the crystal phase of the monoclinic Li 2 MnO 3 type layered rock salt structure and a crystal phase of a cubic rock salt structure. An electrode active material for a lithium ion secondary battery, comprising the lithium nickel manganese composite oxide according to any one of claims 1 to 8. A lithium ion secondary battery comprising the electrode active material for lithium ion secondary batteries according to claim 9. A method for producing the lithium nickel manganese based composite oxide according to any one of claims 1 to 8,
1. A step of forming a precipitate by treating a manganese compound and a nickel compound with an alkali;
Step 2: oxidizing the precipitate to obtain a composite oxide precursor;
A step 3 of heat-treating the composite oxide precursor in an oxidizing atmosphere in the presence of a lithium compound, and a step 4 of heat-treating the product obtained in the step 3 in an inert atmosphere at a higher temperature than in the step 3.
The manufacturing method according to claim 1, The method according to claim 11, further comprising step 5 of heat treating the product obtained in step 4 under a reducing atmosphere at a lower temperature than in step 4.

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