JP7750503B2 - Monoclinic lithium nickel manganese composite oxide containing different metals and its method of manufacture - Google Patents

Description

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

Lithium-ion secondary batteries are useful as secondary batteries for devices such as laptops and smartphones. They are also considered important as batteries for electric vehicles and plug-in hybrid vehicles, as well as system power sources for load leveling systems, and 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 inserted and removed from the positive electrode active material and the amount of positive electrode in the cell determines the battery capacity of the cell, while the operating voltage of the positive electrode active material determines the cell voltage.

Currently, the cathode active materials commonly used in large-capacity lithium-nickel-manganese-cobaltate (NMC) and lithium-nickel-oxide are the two most commonly used materials for large-capacity lithium-nickel-oxide batteries. Compared to NMC, lithium-nickel-oxide cathodes have a higher capacity per weight of cathode active material, but they pose safety concerns during charging. Therefore, NMC cathodes are used in large-capacity prismatic batteries, while lithium-nickel-oxide cathode active materials are only used in small-capacity cylindrical batteries.

Both types of positive electrode active materials contain the element cobalt, which is highly ubiquitous and rare. To mitigate the risk of unstable and rising cobalt raw material prices, there is a strong demand for the development of cobalt-free positive electrode active materials with excellent charge-discharge characteristics. Nickel is also a scarce resource, and its costs have been rising due to the recent race to develop batteries, so there is a similar demand for its reduction.

The present inventors have clarified that _lithium iron manganese _composite oxides (Patent Document 1, etc.), lithium iron nickel manganese composite oxides (Patent Document 2, etc.), and lithium nickel manganese composite oxides (Patent Documents 3-4, Non-Patent Documents 1-3, etc.), which have a monoclinic Li 2 MnO 3 layered rock salt structure, exhibit excellent charge-discharge characteristics.

Japanese Patent Application Laid-Open No. 2009-179501 International Publication No. 2019/235573 Japanese Patent Application Laid-Open No. 2021-017397 International Publication No. 2018/169004

Mitsuharu Tabuchi et al., Electrochimica Acta, 210 (2016) 105-110. Mitsuharu Tabuchi et al., 59th Battery Symposium Abstracts 3D21, (2018) Mitsuharu Tabuchi, Abstracts of the 60th Battery Symposium 2A05, (2019)

However, Patent Document 1 was not satisfactory in terms of operating voltage, charge/discharge capacity, discharge rate characteristics, etc. Furthermore, Patent Document 2 describes that using a specific amount or more of a trivalent or higher manganese compound as a raw material and performing secondary firing in an air atmosphere results in excellent discharge capacity and charge/discharge cycle characteristics, but similar conditions are often not desirable when trying to improve discharge rate characteristics. For this reason, it remains unclear which material should be selected from among heterometal-substituted lithium-nickel-manganese composite oxides to produce secondary batteries that are particularly excellent in operating voltage, charge/discharge capacity, and discharge rate characteristics.

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

As a result of extensive research to achieve the above objective, the inventors discovered that the above problem can be solved by setting the distribution or abundance of metal ions other than lithium, consisting of the dissimilar metals Ni and Mn, in a lithium-nickel-manganese composite oxide containing dissimilar metals, magnesium or titanium, to specific conditions. Based on this finding, the inventors conducted further research and completed the present invention.

That is, the present invention encompasses the following lithium-nickel-manganese composite oxide and its production method.

Item 1. General formula (1):
Li _1+x (Ni _y M _z Mn _1-y-z ) _1-x O ₂ (1)
[In the formula, M represents Mg and/or Ti. x, y, and z represent 0<x<1/3, 0.150≦y≦0.350, and 0.050≦z≦0.150, respectively. However, when M is Mg, 0.150≦y≦0.250.]
and a heterometal-containing 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 crystalline phase of the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the ratio of the X-ray peak intensity, obtained by dividing the peak height of the (020) plane by the height of a single peak consisting of the overlap of the peaks of the (20-2) plane and the (131) plane, is 3.0 to 10.0% when 0.150≦y≦0.250 and the M is Mg, 3.0 to 14.0% when 0.150≦y≦0.250 and the M is Ti, and 3.0 to 8.0% when 0.250<y≦0.350 and the M is Ti.
(2) The sum of the average abundances of metals other than lithium in the lithium layer and the metal-other-than-lithium layer in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure (g _total ) is 0.780 to 0.850 when 0.150≦y≦0.250 and the M is Mg, 0.720 to 0.800 when 0.150≦y≦0.250 and the M is Ti, and 0.750 to 0.820 when 0.250<y≦0.350 and the M is Ti, and (3) in the hexagonal mesh structure in the metal-other-than-lithium layer in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the ratio of the metal occupancy rate other than lithium (g _4g ) at the hexagonal mesh lattice position (4g position) to the metal occupancy rate other than lithium (g _2b When y is 0.150≦y≦0.250 and M is Mg, the value (g _4g −g _2b ) obtained by subtracting y from Mg satisfies at least one of the following: when y is 0.150≦y≦0.250 and M is Ti, the value (g 4g −g 2b ) is 0.230 to 0.300; when y is 0.150≦y≦0.250 and M is Ti, the value (g 4g −g 2b ) ... is 0.250 to 0.390; and when y is 0.250<y≦0.350 and M is Ti, the value (g 4g −g 2b ) satisfies at least one of the following:

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

Item 3. The heterometal-containing lithium _nickel manganese composite oxide according to Item ₂ , wherein the sum (g _total ) of the average amounts of the metals other than lithium present in the lithium layer and the metal other than lithium-lithium layer in the monoclinic Li 2 MnO 3 -type layered rock salt structure is 0.780 to 0.850 when 0.150≦y≦0.250 and M is Mg, 0.720 to 0.800 when 0.150≦y≦0.250 and M is Ti, or 0.750 to 0.820 when 0.250<y≦0.350 and M is Ti.

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

Item 5. The heterometal-containing lithium nickel manganese composite oxide according to any one of Items 2 to 4, wherein in a hexagonal meshwork ordered structure in a metal other than lithium-lithium layer in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the value (g _4g -g _2b ) obtained by subtracting the metal other than lithium occupancy rate (g _4g ) at a hexagonal meshwork lattice central position (position 2b) from the metal other than lithium occupancy rate (g 2b ) at a hexagonal _meshwork lattice constituent position (position 4g ) is 0.230 to 0.300 when 0.150≦y≦0.250 and M is Mg, 0.250 to 0.390 when 0.150≦y≦0.250 and M is Ti, or 0.230 to 0.310 when 0.250<y≦0.350 and M is Ti.

Item 6. The heterometal-containing lithium nickel manganese composite oxide according to Item 1, which satisfies (3) above.

Item 7. The heterometal-containing lithium nickel manganese composite oxide according to any one _of Items 1 to 6, which is constituted by a crystalline phase of the monoclinic Li ₂ MnO ₃ -type layered rock salt structure or a mixed phase of a crystalline phase of the monoclinic Li 2 MnO ₃ -type layered rock salt structure and a crystalline phase of a cubic rock salt structure.

Item 8. An electrode active material for a lithium ion secondary battery, containing the heterometal-containing lithium nickel manganese composite oxide described in any one of Items 1 to 7.

Item 9. A lithium ion secondary battery comprising the electrode active material for a lithium ion secondary battery described in Item 8.

Item 10. A method for producing a different metal-containing lithium nickel manganese composite oxide according to any one of Items 1 to 7, comprising:
Step 1: forming a precipitate by treating a mixture of a magnesium compound and/or a titanium compound, a manganese compound, and a nickel compound with an alkali;
Step 2: oxidizing the precipitate to obtain a composite oxide precursor;
Step 3: heat-treating the composite oxide precursor in an oxidizing atmosphere in the presence of a lithium compound; and Step 4: heat-treating the product obtained in Step 3 in an inert atmosphere at a higher temperature than in Step 3.
A manufacturing method comprising the steps of:

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

(a) A diagram of the b-c plane arrangement of the crystal structure of the lithium nickel manganese composite oxide of the present invention. (b) A diagram of the arrangement within the metal other than lithium (TM)-lithium layer on the a-b plane of the crystal structure of the lithium nickel manganese composite oxide of the present invention. 1 is a measured (+) and calculated (solid line) X-ray diffraction pattern of the lithium nickel manganese composite oxide of Example 1 using CuKα radiation. 1 is a measured (+) and calculated (solid line) X-ray diffraction pattern of the lithium nickel manganese composite oxide of Comparative Example 1 using CuKα radiation. 3 shows the charge-discharge characteristics of a lithium secondary battery using the composite oxide of Example 1 as a positive electrode active material. Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Comparative Example 1 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium secondary battery using the composite oxide of Example 1 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium 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 pattern 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 composite oxide of Comparative Example 2 using CuKα radiation. Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Example 2 as a positive electrode active material. Charging and discharging characteristics of a lithium 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 secondary battery using the composite oxide of Example 2 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium secondary battery using the composite oxide of Comparative Example 2 as a positive electrode active material. 1 is a measured (+) and calculated (solid line) X-ray diffraction pattern of the lithium nickel manganese composite oxide of Example 3 using CuKα radiation. 1 is a measured (+) and calculated (solid line) X-ray diffraction pattern of the lithium nickel manganese composite oxide of Comparative Example 3 using CuKα radiation. 3 shows the charge-discharge characteristics of a lithium secondary battery using the composite oxide of Example 3 as a positive electrode active material. Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Comparative Example 3 as a positive electrode active material. 1 shows the discharge rate characteristics of a lithium secondary battery using the composite oxide of Example 3 as a positive electrode active material. 10 shows the discharge rate characteristics of a lithium secondary battery using the composite oxide of Comparative Example 3 as a positive electrode active material.

In this specification, the term "containing" encompasses the concepts of "comprise," "consist essentially of," and "consist only of." Furthermore, 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 containing different metals)
The heterometal-containing lithium nickel manganese composite oxide of the present invention has the following general formula (1):
Li _1+x (Ni _y M _z Mn _1-y-z ) _1-x O ₂ (1)
[In the formula, M represents Mg and/or Ti. x, y, and z represent 0<x<1/3, 0.150≦y≦0.350, and 0.050≦z≦0.150, respectively. However, when M is Mg, 0.150≦y≦0.250.]
It is expressed as:

The heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention is a heterogeneous metal-containing lithium nickel manganese 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 a first aspect (requirement (3)) of the heterometal-containing lithium nickel manganese composite oxide of the present invention, in the hexagonal mesh structure of the metal-lithium layer other than lithium in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the value (g _4g -g 2b ) obtained by subtracting the occupancy rate of the metal other than lithium at the central position of the hexagonal mesh structure (g _2b ) from the occupancy rate of the metal other than lithium at _the hexagonal mesh structure position (g _4g ) is 0.230 to 0.300 when 0.150≦y≦0.250 and M is Mg, 0.250 to 0.390 when 0.150≦y≦0.250 and M is Ti, and 0.230 to 0.310 when 0.250<y≦0.350 and M is Ti. In the heterometal-containing lithium nickel manganese composite oxide of the present invention in this first aspect, as shown in FIG. 1, the distribution of metal (TM) ions other than lithium consisting of Mg, Ti, Ni, and Mn is different from that of known Li ₂ MnO ₃ .

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

Furthermore, in the hexagonal layered rock-salt crystal structure of conventional NMC positive electrodes, there is only one type of cation lattice position in each of the lithium layer and the metal other than lithium-lithium layer, whereas 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 each of the lithium layer and the metal other than lithium-lithium layer.

In the lithium layer in Figure 1(a), the lattice positions correspond to the 2c and 4h positions, while in the metal-lithium layer other than lithium (TM-Li layer), the lattice positions correspond to the 4g and 2b positions, as shown in Figure 1(b). The heterometal-containing lithium-nickel-manganese composite oxide of the present invention in the first embodiment is characterized by the distribution of metal ions other than lithium within this TM-Li layer.

As shown in Figure 1(b), the 4g position corresponds to a hexagonal mesh lattice component, and the 2b position corresponds to the center position of the _hexagonal mesh lattice. In an ideal _Li2MnO3 structure, only the 4g position contains a metal ion other than lithium, and the 2b position contains a lithium ion. However, in reality, both lattice positions can be occupied by metal ions other than lithium.

In a first aspect of the present invention, the difference (g _4g - g _2b ) between the occupancy rate of a metal ion other than lithium at the 4g position (g 4g ) and the occupancy rate of a metal ion other than lithium at the 2b position (g _2b ) obtained by _{the X-ray Rietveld method is small. The value of (g 4g -} g _2b ) is 0.230 to 0.300, preferably 0.235 to 0.280, when 0.150≦y≦0.250 and M is Mg. The value of (g _4g - g _2b ) is 0.250 to 0.390, preferably 0.300 to 0.380, when 0.150≦y≦0.250 and M is Ti. The value of (g _4g - g _2b ) is 0.230 to 0.310, preferably 0.235 to 0.290, when 0.250 < y ≦ 0.350 and M is Ti. By setting (g _4g - g _2b ) within this range, a high-value Mn source with a valence of 3 or more is not required, allowing the use of an inexpensive divalent Mn source, which is industrially advantageous. In addition, the production of electrochemically inactive Li ₂ MnO ₃ -rich components is suppressed, and samples with high initial charge/discharge capacities and high discharge rate characteristics after charge/discharge cycles are easily obtained.

Furthermore, within the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, metals other than lithium are present at the 2c and 4h positions within the lithium layer, and as described above, metals other than lithium are also present at the 4g and 2b positions within the non-lithium metal-lithium layer. The amount of metal other than lithium (g _total ) per composition formula is defined as the sum of the average amount of metal other than lithium within the lithium layer ((2g _4h + g _2c )/3) and the average amount of metal other than lithium within the non-lithium metal-lithium layer ((2g _4g + g _2b )/3). Setting this value within a predetermined range is also effective for improving charge-discharge characteristics (particularly the initial charge-discharge capacity and charge-discharge capacity after charge-discharge cycles, as well as the discharge rate characteristics). On the other hand, this value increases as the valence and content of the constituent heterometals decrease, so the optimal value varies depending on the heterometal species and their content. Specifically, in the heterometal-containing lithium nickel manganese composite oxide of the present invention in the second aspect (requirement (2)), the g _total value is 0.780 to 0.850, preferably 0.785 to 0.830, when 0.150≦y≦0.250 and M is Mg. The _{g total} value is 0.720 to 0.800, preferably 0.725 to 0.780, when 0.150≦y≦0.250 and M is Ti. The _{g total} value is 0.750 to 0.820, preferably 0.755 to 0.800, when 0.250<y≦0.350 and M is Ti. By setting the g _total value within this range, the generation of electrochemically inactive Li ₂ MnO ₃ -rich components is suppressed, and the lithium content per composition formula is sufficiently large, so that the initial charge/discharge capacity and the charge/discharge capacity after charge/discharge cycles are high, and it is easy to obtain a sample with high discharge rate characteristics.

Furthermore, the heterometal-containing lithium nickel manganese-based composite oxide of the present invention preferably has as low an X-ray peak intensity ratio as possible. The X-ray peak intensity ratio is calculated by dividing the peak height of the (020) plane peak due to the hexagonal network structure observed near 2θ = 20° in an X-ray diffraction pattern using CuKα radiation by the height of a single peak consisting of the overlap of the (20-2) and (131) plane peaks observed near 2θ = 45°. This X-ray peak intensity ratio tends to increase as the heterometal valence and its content decrease, so the optimal value varies depending on the heterometal type and its content. Therefore, in the heterometal-containing lithium nickel manganese-based composite oxide of the present invention in the third aspect (requirement (1)), this X-ray peak intensity ratio is 10.0% or less, preferably 9.0% or less, when 0.150 ≦ y ≦ 0.250 and M is Mg. This X-ray peak intensity ratio is 14.0% or less, preferably 13.5% or less, when 0.150 ≦ y ≦ 0.250 and M is Ti. When 0.250<y≦0.350 and M is Ti, the ratio of this X-ray peak intensity is 8.0% or less, preferably 7.5% or less. By setting the ratio within this range, the production of the electrochemically inactive Li ₂ MnO ₃ component is suppressed, and it is easy to obtain a sample having the desired initial charge/discharge capacity and after charge/discharge cycles, as well as high discharge rate characteristics. There is no particular limitation on the lower limit of this X-ray peak intensity ratio, and it is preferably, for example, 3.0%.

In general formula (1), x represents the amount of excess lithium, specifically 0 < x < 1/3. By setting the value of x within this range, lithium can be easily incorporated into the structure without using more lithium than necessary, and it is less likely to remain in the product as an impurity phase, which is advantageous from a cost perspective. Furthermore, it is preferable that x be between 0.05 and 0.30.

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

For example, when an oxide represented by a specific composition formula is produced using the coprecipitation-calcination method described below, a heterometal-containing 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 metal other than lithium-lithium layer in a monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the value (g _4g -g 2b ) obtained by subtracting the occupancy rate of a metal other than lithium at the center position of the hexagonal mesh structure (g _2b ) from the occupancy rate of a metal other than lithium at _the hexagonal mesh structure position (g _4g ) is 0.230 to 0.300 when 0.150≦y≦0.250 and M is Mg, 0.250 to 0.390 when 0.150≦y≦0.250 and M is Ti, and 0.230 to 0.310 when 0.250<y≦0.350 and M is Ti (requirement (3)), and monoclinic Li ₂ MnO The ratio of the X-ray peak intensity, which is obtained by dividing the peak height of the (020) plane peak observed around 2θ=20° in the X-ray diffraction pattern of the crystalline phase of the Li 2 MnO ₃ type layered rock salt structure by the height of a single peak consisting of the overlap of the peaks of the (20-2) plane and the (131) plane observed around 2θ=45°, is 3.0 to 10.0% when 0.150≦y≦0.250 and M is Mg, 3.0 to 14.0% when 0.150≦y≦0.250 and M is Ti, and 3.0 to 8.0% when 0.250<y≦0.350 and M is Ti (requirement (1)), and the sum of the average abundances of the lithium layer and the metal other than lithium in the metal other than lithium-lithium layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure (g _total ) is 0.780 to 0.850 when 0.150≦y≦0.250 and M is Mg, 0.720 to 0.800 when 0.150≦y≦0.250 and M is Ti, and 0.750 to 0.820 when 0.250<y≦0.350 and M is Ti (requirement (2)).

To stabilize the distribution of metal ions other than lithium, the amount of nickel ions y per total amount of metals other than lithium is 0.150≦y≦0.350, 0.150≦y≦0.250, preferably 0.175≦y≦0.225, or 0.250<y≦0.350, preferably 0.275≦y≦0.325. However, when M is Mg, to stabilize the distribution of metal ions other than lithium, the amount of nickel ions y per total amount of metals other than lithium is 0.150≦y≦0.250, preferably 0.175≦y≦0.225. By setting y within this range, the distribution of metal ions other than lithium in the metal-lithium layer other than lithium can be stabilized without increasing the amount of Mn in the composition formula, while still adequately maintaining the discharge potential-increasing effect of nickel ions. This allows for a sufficient amount of lithium ions in the composition formula, resulting in improved charge/discharge capacity.

The heterometal-containing lithium nickel manganese composite oxide of the present invention is preferably composed of a crystalline phase having the monoclinic _{Li2MnO3 -} type layered rock salt structure, or a mixed phase of a crystalline phase having the monoclinic _{Li2MnO3 -} type layered rock salt structure and a crystalline phase having a cubic rock salt structure.

In other words, the heterometal-containing lithium nickel manganese composite oxide preferably contains a crystalline phase of the monoclinic _{Li2MnO3 -} type layered rock salt structure described above. Of course, a mixed phase containing other rock salt crystal structures is also preferred. Specifically, a mixed phase further containing a crystalline phase of a cubic rock salt structure represented by the space group of the following formula (c) is also preferred.

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 approximately monoclinic Li ₂ MnO ₃ -type layered rock salt structure crystal phase:cubic rock salt structure crystal phase (mass ratio) = 100:0 to 10:90. The heterometal-containing 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 (approximately 0.01 to 10 mass%, assuming that the total amount of crystalline phases whose peaks 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 below, a heterometal-containing lithium nickel manganese 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, approximately 90 to 99.9 mass %, assuming that the total amount of crystalline phases in which peaks can be confirmed in the X-ray diffraction pattern is 100 mass %).

(2. Electrode active material for lithium ion secondary battery and lithium ion secondary battery)
The heterometal-containing 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 heterometal-containing lithium-nickel-manganese composite oxide of the present invention as the positive electrode active material. Specifically, a lithium-ion secondary battery can be assembled by a conventional method using the heterometal-containing lithium-nickel-manganese composite oxide of the present invention as the positive electrode active material, known lithium metal, lithium titanate, silicon, silicon oxide, carbon-based materials (graphite-based materials, non-graphitic materials), etc. as the negative electrode active material, and known organic electrolyte solutions such as those prepared by dissolving lithium salts such as lithium perchlorate or _LiPF6 in solvents such as ethylene carbonate or dimethyl carbonate, polymer electrolytes, sulfide solid electrolytes, and other known battery components.

(3. Method for producing a lithium-nickel-manganese composite oxide containing different metals)
The method for producing a lithium-nickel-manganese-based composite oxide containing different metals of the present invention comprises, in this order, for example, Step 1 of forming a precipitate by adjusting the alkalinity of a mixture of a magnesium compound and/or a titanium compound, 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 in an oxidizing atmosphere in the presence of a lithium compound; and Step 4 of heat-treating the product obtained in Step 3 in an inert atmosphere at a higher temperature than in Step 3.

(3.1. Process 1)
In step 1, a mixture of a magnesium compound and/or a titanium compound, a manganese compound, and a nickel compound is treated with alkali to form a precipitate.

The magnesium compound, titanium compound, manganese compound, and nickel compound function as the magnesium source, titanium source, manganese source, and nickel source, respectively, for the heterometal-containing lithium-nickel-manganese composite oxide. A wide variety of known metal salts of magnesium, titanium, manganese, and nickel can be used, and there are no particular limitations. For example, from a cost perspective, it is preferable to use divalent salts (sulfates, nitrates, chlorides, acetates, and hydrates thereof, etc.). Potassium permanganate(VII), manganese(III) acetate, manganese(III) acetylacetate, etc. may also be used as a high-valence Mn source. Other examples include magnesium metal, titanium metal, manganese metal, or nickel metal, as well as oxides of magnesium, titanium, manganese, or nickel. It is also preferable to use magnesium metal, titanium metal, manganese metal, or nickel metal, or oxides thereof dissolved in acid as metal salts. The magnesium compound, titanium compound, manganese compound, and nickel compound may all be used singly or in combination.

The mixing ratio of the magnesium compound, titanium compound, manganese compound, and nickel compound used is preferably the same as the compounding ratio of magnesium, titanium, manganese, and nickel in the desired heterometal-containing lithium nickel manganese composite oxide.

As described above, the production method of the present invention is likely to produce a different metal-containing lithium nickel manganese composite oxide that satisfies all of the above requirements (1) to (3). Specifically, in a hexagonal mesh structure in a metal other than lithium-lithium layer in a monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the value (g _4g -g 2b ) obtained by subtracting the occupancy rate of a metal other than lithium at the center position of the hexagonal mesh structure (g _2b ) from the occupancy rate of a metal other than lithium at _the hexagonal mesh structure position (g _4g ) is 0.230 to 0.300 when 0.150≦y≦0.250 and M is Mg, 0.250 to 0.390 when 0.150≦y≦0.250 and M is Ti, and 0.230 to 0.310 when 0.250<y≦0.350 and M is Ti (requirement (3)), and monoclinic Li ₂ MnO The ratio of the X-ray peak intensity, which is obtained by dividing the peak height of the (020) plane peak observed around 2θ=20° in the X-ray diffraction pattern of the crystalline phase of the Li 2 MnO ₃ type layered rock salt structure by the height of a single peak consisting of the overlap of the peaks of the (20-2) plane and the (131) plane observed around 2θ=45°, is 3.0 to 10.0% when 0.150≦y≦0.250 and M is Mg, 3.0 to 14.0% when 0.150≦y≦0.250 and M is Ti, and 3.0 to 8.0% when 0.250<y≦0.350 and M is Ti (requirement (1)), and the sum of the average abundances of the lithium layer and the metal other than lithium in the metal other than lithium-lithium layer in the monoclinic Li ₂ MnO ₃ type layered rock salt structure (g _total ) is 0.780 to 0.850 when 0.150≦y≦0.250 and M is Mg, 0.720 to 0.800 when 0.150≦y≦0.250 and M is Ti, and 0.750 to 0.820 when 0.250<y≦0.350 and M is Ti (requirement (2)).

From the above, the above parameters can be appropriately selected depending on the required physical properties and characteristics of the resulting lithium-nickel-manganese composite oxide containing different metals of the present invention.

The magnesium compound, titanium compound, manganese compound, and nickel compound are preferably prepared as a mixture containing a magnesium compound and/or titanium compound, a manganese compound, and a nickel compound. It is more preferable to dissolve them in an appropriate solvent to prepare a mixed solution of a magnesium compound and/or titanium compound, a manganese compound, and a nickel compound. It is even more preferable to dissolve them in water to prepare a mixed aqueous solution of a magnesium compound and/or titanium compound, a manganese compound, and a nickel compound. There are no particular limitations on the concentration of the mixed aqueous solution; for example, the total concentration of the magnesium compound, titanium compound, manganese compound, and nickel compound is preferably 0.01 to 5 mol/L, and more preferably 0.1 to 2.0 mol/L.

A mixture containing a magnesium compound and/or titanium compound, a manganese compound, and a nickel compound is preferably prepared as a mixed liquid, more preferably as a mixed aqueous solution, and then treated with alkali to form a precipitate. The alkali treatment can be achieved by making the mixture (preferably a mixed liquid, more preferably a mixed aqueous solution) containing the magnesium compound and/or titanium compound, the manganese compound, and the nickel compound alkaline.

When treating a mixture containing at least one compound selected from the group consisting of magnesium compounds and/or titanium compounds, a manganese compound, and a nickel compound with alkali, the pH can be set appropriately, taking into consideration the type and concentration of the compounds. Specifically, a pH of 8 or higher is preferred, and a pH of 11 or higher is more preferred. 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 alkaline treatment. For example, a method can be used in which a mixture containing a magnesium compound and/or titanium compound, a manganese compound, and a nickel compound is gradually added to an alkaline aqueous solution. When using this method, it is preferable to use a liquid pump, for example, 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 using this method, a uniform precipitate can be obtained.

There are no particular restrictions on the alkaline substance used in the alkaline treatment, and examples that can be used include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, lithium hydroxide, and lithium hydroxide monohydrate, as well as ammonia. These alkaline substances are preferably dissolved in an appropriate solvent and used as an alkaline solution with 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 it is also preferable to use a water-alcohol mixed solvent in addition to water. The alcohol used here is preferably a water-soluble alcohol such as ethanol or methanol. While using water is simple, using a water-alcohol mixed solvent allows the alcohol to function as an antifreeze, making it easier to form precipitates at temperatures below 0°C. Furthermore, by adding alcohol, the alcohol functions as a reducing agent, making it easier to form precipitates using potassium permanganate(VII), a source of high-valent Mn.

The amount of alcohol used in the water-alcohol mixed solvent can be set appropriately depending on 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 during precipitation, it is preferable to control the temperature during precipitation using a thermostatic bath or similar. The set temperature during alkaline treatment is preferably between -20 and 80°C, and more preferably between -10 and 60°C.

(3.2. Process 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 subject the reaction system containing the precipitate to an oxidation treatment. This 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 a period of preferably 0.5 to 7 days, more preferably 1 to 4 days.

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

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

(3.3. Process 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.

There are no particular limitations on the lithium compound used, and lithium salts can be used, for example. More specific examples include lithium carbonate, lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, and lithium acetate.

The amount of lithium compound used relative to the molar amount of metal compounds other than lithium is not particularly limited. However, it is preferable to use (Li/(Ni+M+Mn) (molar ratio)) as a value obtained by assuming, for example, yNiO-zMO-(1-y-z)Li ₂ MnO ₃ , where the valence of the different metals is divalent (when M is Mg), nickel is divalent, and manganese is tetravalent. For example, when y is 0.200 and z is 0.100, from the above solid composition, (Li/(Ni+M+Mn) (molar ratio)) = 0.30 × 0 + 0.70 × 2 = 1.40
By using the above, the water washing treatment after the heat treatment in step 4 described below is not necessary, thereby simplifying the process. On the other hand, the Li/(Ni+M+Mn) (molar ratio) can be appropriately changed to obtain the desired charge/discharge characteristics. For example, the Li/(Ni+M+Mn) (molar ratio) may be set to a value in excess of the target composition, such as 2.00, and the excess lithium salt may be removed after the heat treatment by water washing, filtration, drying, etc.

The composite oxide precursor and the lithium compound may be dry-mixed and the resulting mixture subjected to heat treatment, but 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, then add the composite oxide precursor and mix to form a slurry.

The resulting slurry is preferably dried to form a dry mixture before heat treatment. Drying conditions are not particularly limited. For example, gradual drying at a temperature of 40 to 60°C is preferred, as this makes it easier to prevent separation of the lithium salt and precipitate, which have different specific gravities.

Then, the mixture of the composite oxide precursor and the lithium compound, or the dried mixture obtained by drying the slurry, is heat-treated in an oxidizing atmosphere. If the dried mixture is heat-treated, it is preferable to perform a pulverization process before the heat treatment. There are no particular restrictions on the conditions for the pulverization process, as long as 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 oxidizing atmospheres 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. Process 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 restrictions on the inert atmosphere, so long as it suppresses oxidation at high temperatures. Examples of the inert atmosphere include nitrogen and 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 and reduction effects will not be achieved, and a sample with excellent charge-discharge cycle characteristics will not be obtained.

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.

The above describes embodiments of the present invention, but 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 embodiments of the present invention based on examples, but the present invention is not limited to these examples.

Example 1
14.54 g of nickel(II) nitrate hexahydrate, 6.41 g of magnesium(II) nitrate hexahydrate, and 34.63 g of manganese(II) chloride tetrahydrate (total amount 0.25 mol, Ni:Mg:Mn molar ratio = 20:10:70) were added to 500 mL of distilled water and completely dissolved to obtain a Ni-Mg-Mn aqueous solution (0.50 mol/L). A sodium hydroxide aqueous solution (50 g of sodium hydroxide dissolved in 500 mL of distilled water; 2.50 mol/L) was prepared in a separate beaker. This sodium hydroxide aqueous solution was placed in a titanium beaker and, while stirring, placed in a thermostatic bath, which was maintained at +20°C. Next, the Ni-Mg-Mn aqueous solution was gradually added dropwise to the sodium hydroxide aqueous solution over 2 to 3 hours to form a Ni-Mg-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 for 48 hours or more while stirring, thereby subjecting the coprecipitate to wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. 200 mL of distilled water was added to the resulting material, which was then mixed with 1.00 times (molar ratio) lithium carbonate (18.47 g; Li/(Ni + Mg + Mn) (molar ratio) 2.00) in a mixer to create a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) dish and dried at 50°C for two days.

The dried powder was pulverized 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 and pulverized again in a vibration mill, before being placed in an electric furnace and subjected to secondary firing in a nitrogen stream at 850°C for 5 hours (step 4). The powder was then removed from the electric furnace and pulverized again in a vibration mill, then washed with distilled water, filtered, and dried to obtain a magnesium-containing lithium-nickel-manganese composite oxide.

(Comparative Example 1)
In the secondary firing in step 4, the inert atmosphere of nitrogen was changed to air, and the same preparation as in Example 1 was carried out to obtain a magnesium-containing lithium nickel manganese composite oxide.

X-ray diffraction measurement (Example 1)
Figure 2 shows 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.) with the calculated pattern (solid line) obtained using a monoclinic Li ₂ MnO ₃ unit cell (peak positions are indicated by vertical bars, and the residual between the measured and calculated values is indicated near the intensity of 0). The difference between the measured and calculated values was small, confirming that reliable analytical values were obtained. The obtained lattice constants were a = 4.9578(4) Å, b = 8.5632(5) Å, c = 5.0245(3) Å, β = 109.210(6)°, and the lattice volume was V = 201.4(4) Å ³ . The metal (assuming virtual atoms Ni _0.20 Mg _0.10 Mn _0.70 ) occupancy rate 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 (Comparative Example 1)
A comparison (solid line) of the measured pattern (+) of Comparative Example 1 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern (solid line) obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in Figure 3 (peak positions are indicated by vertical bars, and the residual between the measured and calculated values is indicated near an intensity of 0). The difference between the measured and calculated values was small, confirming that reliable analytical values were obtained. The obtained lattice constants were a = 4.9447(5) Å, b = 8.5515(5) Å, c = 5.0217(3) Å, β = 109.168(9)°, and the lattice volume was V = 200.6(6) Å ^3. The occupancy of metals other than lithium (assuming virtual atoms Ni _0.20 Mg _0.10 Mn _0.70 ) at each lattice site was calculated assuming an isotropic thermal vibration parameter B of 1, as shown in Table 1 below.

As shown in Table 1, the composite oxide of Example 1 has a difference g _4g -g _2b between the occupancy rate of the hexagonal network constituent position (4g position) and the occupancy rate of the hexagonal network center position (2b position) of 0.244, which is clearly within the scope of the present invention. Furthermore, the ratio I 020 /I 20-2,131 of the height of a single peak consisting of the overlap of the peak of the (020) plane near 2θ = 20° and the peaks of the ( _20-2 ) and ( ₁₃₁ ) planes near 2θ = 45° is 7.58%, which is clearly within the scope of the present invention. Furthermore, the amount of metal other than lithium per composition formula (g total ), defined as the sum of the average amount of metal in the lithium layer ((2g _4h +g _2c )/3) and the average amount of metal other than lithium in the lithium layer (( _{2g 4g} +g _2b )/3), is 0.799, which is clearly within the scope of the present invention.

Furthermore, with regard to 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 hexagonal network center position (2b position) is 0.355, which is clearly outside the scope of the present invention. Furthermore, the ratio I 020 /I _20-2,131 of the height of the single peak consisting of the overlap of the (020) plane peak near 2θ = 20 ° and the (20-2) plane and (131) plane peak near 2θ = ₄₅ ° is 10.95%, which is clearly outside the scope of the present invention. Furthermore, the metal amount (g total ) per composition formula defined as the sum of the average metal amount in the lithium layer ((2g _4h + g _2c ) / 3) and the metal other than lithium - average metal amount in the lithium layer ((2g _{4g + g 2b )} / 3) is 0.772, which is clearly outside the scope of the present invention. Therefore, it is understood that step 4 must be carried out under an inert atmosphere.

Chemical Analysis (Example 1 and Comparative Example 1)
The metal amounts of the magnesium-containing lithium nickel manganese composite oxides of Example 1 and Comparative Example 1 were 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+Mg+Mn) (molar ratio) using the following formula:
x=(Li/(Ni+Mg+Mn)-1)/(Li/(Ni+Mg+Mn)+1)
On the other hand, the y value is Ni/(Ni+Mg+Mn) (molar ratio) itself, and the z value is Mg/(Ni+Mg+Mn) (molar ratio) itself. It is clear that Example 1 falls within the range of the composition formula of the present invention.

Evaluation of charge/discharge characteristics (Example 1 and Comparative Example 1)
20 mg of the magnesium-containing lithium-nickel-manganese composite oxides from Example 1 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 mixture was then pressed onto an aluminum mesh to prepare a composite electrode. The composite electrode was vacuum dried overnight at 120°C and then placed in a glove box with a dew point of -80°C or below. A coin-type lithium secondary battery was assembled using metallic lithium as the negative electrode and 1M _LiPF6 dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio ethylene carbonate:dimethyl carbonate = 3:7) as the electrolyte. The fabricated battery was removed from the glove box and connected to a charge/discharge tester. A charge/discharge test was performed at 30°C at the start of charging and a current density of 40 mA/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. From the sixth cycle onwards, the battery was charged and discharged 29 times at a constant current within the potential range of 2.0-4.6 V.

The charge-discharge characteristics of lithium secondary batteries using the magnesium-containing lithium-nickel-manganese composite oxides of Example 1 and Comparative Example 1 as the positive electrode active material are shown in Figures 4 and 5, respectively. In both Figures 4 and 5, the curves sloping upward to the right indicate the charge curves (denoted by the subscript c), and the curves sloping downward to the right indicate the discharge curves (denoted by the subscript d). Numbers indicate the number of cycles. Cycles 1 to 4 are not shown because they are cycles for electrochemical activation. The charge-discharge capacities of Example 1 and Comparative Example 1 are shown in Table 3 below.

Figures 4 and 5 and Table 3 show that the lithium secondary battery of Example 1 had a larger charge/discharge capacity from the 5th to 34th cycles than the lithium secondary battery of Comparative Example 1, and the change in the charge/discharge curve over the cycles was smaller. Furthermore, the average discharge voltage of the lithium secondary battery of Example 1 at the 5th cycle was 3.48 V, which was almost the same as the value (3.45 V) of the lithium secondary battery of Comparative Example 1.

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

Figures 6 and 7 and Table 4 show the discharge rate characteristics of the lithium secondary batteries of Example 1 and Comparative Example 1.

From Figures 6 and 7 and Table 4, it is clear that the lithium secondary battery of Example 1 has a larger discharge capacity at each current density and superior discharge rate characteristics compared to the lithium secondary battery of Comparative Example 1.

Example 2
14.54 g of nickel(II) nitrate hexahydrate, 20.00 g of 30% aqueous titanium(IV) sulfate solution, and 34.63 g of manganese(II) chloride tetrahydrate (total amount: 0.25 mol, Ni:Ti:Mn molar ratio = 20:10:70) were added to 500 mL of distilled water and completely dissolved to obtain a Ni-Ti-Mn aqueous solution (0.50 mol/L). A sodium hydroxide aqueous solution (50 g of sodium hydroxide dissolved in 500 mL of distilled water; 2.50 mol/L) was prepared in a separate beaker. This sodium hydroxide aqueous solution was placed in a titanium beaker and, while stirring, placed in a thermostatic bath, which was maintained at +20°C. Next, the Ni-Ti-Mn aqueous solution was gradually added dropwise to the sodium hydroxide aqueous solution over 2 to 3 hours to form a Ni-Ti-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 for 48 hours or more while stirring, thereby subjecting the coprecipitate to wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. 200 mL of distilled water was added to the resulting material, which was then mixed with 1.00 times (molar ratio) lithium carbonate (18.47 g; Li/(Ni + Ti + Mn) (molar ratio) 2.00) in a mixer to create a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) dish and dried at 50°C for two days.

The dried powder was pulverized 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 and pulverized again in a vibration mill, before being placed in an electric furnace and subjected to secondary firing in a nitrogen stream at 900°C for 5 hours (Step 4). The powder was then removed from the electric furnace and pulverized again in a vibration mill, then washed with distilled water, filtered, and dried to obtain a titanium-containing lithium-nickel-manganese composite oxide.

(Comparative Example 2)
The secondary firing in step 4 was carried out in the same manner as in Example 2, except that the inert nitrogen atmosphere was changed to air, to obtain a titanium-containing lithium nickel manganese composite oxide.

X-ray diffraction measurement (Example 2)
A comparison (solid line) of the measured pattern (+) of Example 2 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in Figure 8 (peak positions are indicated by vertical bars, and the residual between the measured and calculated values is indicated near the intensity of 0). The difference between the measured and calculated values was small, confirming that reliable analytical values were obtained. The obtained lattice constants were a = 4.9486(3) Å, b = 8.5568(3) Å, c = 5.02475(19) Å, β = 109.291(4)°, and lattice volume V = 201.1(3) Å ^3. The occupancy of metals other than lithium (assuming virtual atoms Ni _0.20 Ti _0.10 Mn _0.70 ) at each lattice site was calculated assuming an isotropic thermal vibration parameter B of 1, as shown in Table 5 below.

X-ray diffraction measurement (Comparative Example 2)
A comparison (solid line) of the measured pattern (+) of Comparative Example 2 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern (solid line) obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in Figure 9 (peak positions are indicated by vertical bars, and the residual between the measured and calculated values is indicated near the intensity of 0). The difference between the measured and calculated values was small, confirming that reliable analytical values were obtained. The obtained lattice constants were a = 4.9443(2) Å, b = 8.5584(2) Å, c = 5.02894(16) Å, β = 109.293(3)°, and lattice volume V = 200.85(18) Å ^3. The occupancy of metals other than lithium (assuming virtual atoms Ni _0.20 Ti _0.10 Mn _0.70 ) at each lattice site was calculated assuming an isotropic thermal vibration parameter B of 1, as shown in Table 5 below.

As shown in Table 5, the composite oxide of Example 2 has a 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) of 0.376, which is clearly within the scope of the present invention. The ratio I 020 /I 20-2,131 of the height of a single peak consisting of the overlap 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 13.32%, which is clearly within the scope of the present invention. In addition, the amount of metal other than lithium per composition formula (g total ) defined as the sum of the average metal amount in the lithium layer ((2g _4h + g _2c ) / 3) and the average metal amount in the metal other than lithium - lithium layer ((2g _{4g + g 2b )} / 3) is 0.736, which is clearly within the scope of the present invention.

Furthermore, with regard to the composite oxide of Comparative Example 2, as shown in 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 0.404, which is clearly outside the scope of the present invention. The ratio I 020 /I _20-2,131 of the height of the single peak consisting of the overlap of the (020) plane peak near 2θ = 20 ° and the (20-2) plane and (131) plane peak near 2θ = ₄₅ ° is 15.25%, which is clearly outside the scope of the present invention. Furthermore, the metal amount (g total ) per composition formula defined as the sum of the average metal amount in the lithium layer ((2g _4h + g _2c ) / 3) and the metal other than lithium - _average metal amount in the lithium layer ((2g _4g + g _2b ) / 3) is 0.713, which is clearly outside the scope of the present invention. Therefore, it is understood that step 4 must be carried out under an inert atmosphere.

Chemical Analysis (Example 2 and Comparative Example 2)
The metal amounts of the titanium-containing lithium nickel manganese composite oxides of Example 2 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+Ti+Mn) (molar ratio) using the following formula:
x=(Li/(Ni+Ti+Mn)-1)/(Li/(Ni+Ti+Mn)+1)
On the other hand, the y value is Ni/(Ni+Ti+Mn) (molar ratio) itself, and the z value is Ti/(Ni+Ti+Mn) (molar ratio) itself. It is clear that the composite oxide of Example 2 falls within the range of the composition formula of the present invention.

Evaluation of charge/discharge characteristics (Example 2 and Comparative Example 2)
Using the titanium-containing lithium nickel manganese composite oxides of Example 2 and Comparative Example 2, electrodes were produced, batteries were produced, and charge/discharge test conditions were set in the same manner as in Example 1, and then a charge/discharge test was carried out.

The charge-discharge characteristics of lithium secondary batteries using the titanium-containing lithium-nickel-manganese composite oxides of Example 2 and Comparative Example 2 as the positive electrode active material are shown in Figures 10 and 11, respectively. In both Figures 10 and 11, the curves sloping upward to the right represent the charge curves (denoted by the subscript c), and the curves sloping downward to the right represent the discharge curves (denoted by the subscript d). Numbers indicate the number of cycles. Cycles 1 to 4 are not shown because they are cycles for electrochemical activation. The charge-discharge capacities of Example 2 and Comparative Example 2 are shown in Table 7 below.

From Figures 10 and 11 and Table 7, it can be seen that the lithium secondary battery of Example 2 had a larger charge/discharge capacity at the 5th cycle than the lithium secondary battery of Comparative Example 2, and showed approximately the same charge/discharge capacity at the 14th cycle, with little change in the shape of the charge/discharge curve over the course of cycles. Furthermore, the average discharge voltage at the 5th cycle of the lithium secondary battery of Example 2 was 3.47 V, which was higher than the value (3.42 V) of the lithium secondary battery of Comparative Example 2.

Evaluation of Discharge Rate Characteristics Next, the discharge rate characteristics under high current density conditions were evaluated in the same manner as in Example 1 using the lithium secondary batteries of Example 2 and Comparative Example 2.

Figures 12 and 13 and Table 8 show the discharge rate characteristics of the lithium secondary batteries of Example 2 and Comparative Example 2.

From Figures 12 and 13 and Table 8, it is clear that the lithium secondary battery of Example 2 has a larger discharge capacity at each current density and superior discharge rate characteristics compared to the lithium secondary battery of Comparative Example 2.

Example 3
21.81 g of nickel(II) nitrate hexahydrate, 20.00 g of 30% titanium(IV) sulfate aqueous solution, and 29.69 g of manganese(II) chloride tetrahydrate (total amount: 0.25 mol, Ni:Ti:Mn molar ratio = 30:10:60) were added to 500 mL of distilled water and completely dissolved to obtain a Ni-Ti-Mn aqueous solution (0.50 mol/L). A sodium hydroxide aqueous solution (2.50 mol/L solution prepared by dissolving 50 g of sodium hydroxide in 500 mL of distilled water) was prepared in a separate beaker. This sodium hydroxide aqueous solution was placed in a titanium beaker and, while stirring, placed in a thermostatic bath, which was maintained at +50°C. The Ni-Ti-Mn aqueous solution was then slowly added dropwise to the sodium hydroxide aqueous solution over 2 to 3 hours to form a Ni-Ti-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 for 48 hours or more while stirring, thereby subjecting the coprecipitate to wet oxidation treatment, thereby aging the precipitate and obtaining the target precursor (Step 2).

The precursor was washed with distilled water and filtered. 200 mL of distilled water was added to the resulting material, which was then mixed with 1.00 times (molar ratio) lithium carbonate (18.47 g; Li/(Ni + Ti + Mn) (molar ratio) 2.00) in a mixer to create a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) dish and dried at 50°C for two days.

The dried powder was pulverized 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 and pulverized again in a vibration mill, before being placed in an electric furnace and subjected to secondary firing in a nitrogen stream at 850°C for 5 hours (step 4). The powder was then removed from the electric furnace and pulverized again in a vibration mill, then washed with distilled water, filtered, and dried to obtain a titanium-containing lithium-nickel-manganese composite oxide.

(Comparative Example 3)
The secondary firing in step 4 was carried out in the same manner as in Example 3, except that the inert nitrogen atmosphere was changed to air, to obtain a titanium-containing lithium nickel manganese composite oxide.

X-ray diffraction measurement (Example 3)
A comparison (solid line) of the measured pattern (+) of Example 3 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 14 (peak positions are indicated by vertical bars, and the residual between the measured and calculated values is indicated near the intensity of 0). The difference between the measured and calculated values was small, confirming that reliable analytical values were obtained. The obtained lattice constants were a = 4.9665(3) Å, b = 8.5966(4) Å, c = 5.03574(17) Å, β = 109.300(5)°, and lattice volume V = 202.9(3) Å ^3. The occupancy of metals other than lithium (assuming virtual atoms Ni _0.30 Ti _0.10 Mn _0.60 ) at each lattice site was calculated assuming an isotropic thermal vibration parameter B of 1, as shown in Table 9 below.

X-ray diffraction measurement (Comparative Example 3)
A comparison (solid line) of the measured pattern (+) of Comparative Example 3 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern obtained using a monoclinic Li ₂ MnO ₃ unit cell is shown in FIG. 15 (peak positions are indicated by vertical bars, and the residual between the measured and calculated values is indicated near the intensity of 0). The difference between the measured and calculated values was small, confirming that reliable analytical values were obtained. The obtained lattice constants were a = 4.9445(3) Å, b = 8.5639(3) Å, c = 5.0221(2) Å, β = 109.295(4) °, and lattice volume V = 200.7(3) Å ^3. The occupancy of metals other than lithium (assuming virtual atoms Ni _0.30 Ti _0.10 Mn _0.60 ) at each lattice site was calculated assuming an isotropic thermal vibration parameter B of 1, as shown in Table 9 below.

As shown in Table 9, the composite oxide of Example 3 has a 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) of 0.273, which is clearly within the scope of the present invention. The ratio I 020 /I 20-2,131 of the height of a single peak consisting of the overlap 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 6.074%, which is clearly within the scope of the present invention. In addition, the amount of metal other than lithium per composition formula (g total ) defined as the sum of the average metal amount in the lithium layer ((2g _4h + g _2c ) / 3) and the average metal amount other than lithium in the lithium layer ((2g _{4g + g 2b )} / 3) is 0.792, which is clearly within the scope of the present invention.

Furthermore, with regard to the composite oxide of Comparative Example 3, as shown in Table 9, 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 0.312, which is clearly outside the scope of the present invention. The ratio I 020 /I _20-2,131 of the height of a single peak consisting of the overlap of the (020) plane peak near 2θ = 20 ° and the (20-2) plane and (131) plane peak near 2θ = ₄₅ ° is 8.901%, which is clearly outside the scope of the present invention. Furthermore, the metal amount (g total ) per composition formula defined as the sum of the average metal amount in the lithium layer ((2g _4h + g _2c ) / 3) and the metal other than lithium - _average metal amount in the lithium layer ((2g _4g + g _2b ) / 3) is 0.744, which is clearly outside the scope of the present invention. Therefore, it is understood that step 4 must be carried out under an inert atmosphere.

Chemical Analysis (Example 3 and Comparative Example 3)
The metal amounts of the titanium-containing lithium nickel manganese composite oxides of Example 3 and Comparative Example 3 were determined by ICP emission spectrometry, and the results are shown in Table 10. The x value in the table was calculated from Li/(Ni+Ti+Mn) (molar ratio) using the following formula:
x=(Li/(Ni+Ti+Mn)-1)/(Li/(Ni+Ti+Mn)+1)
On the other hand, the y value is Ni/(Ni+Ti+Mn) (molar ratio) itself, and the z value is Ti/(Ni+Ti+Mn) (molar ratio) itself. It is clear that the composite oxide of Example 3 falls within the range of the composition formula of the present invention.

Evaluation of charge/discharge characteristics (Example 3 and Comparative Example 3)
Using the titanium-containing lithium nickel manganese composite oxides of Example 3 and Comparative Example 3, electrodes were fabricated, batteries were fabricated, and charge/discharge test conditions were set in the same manner as in Example 1, followed by charge/discharge tests. The electrolyte used was a solution of 1.5 M _LiPF6 dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio of ethylene carbonate:dimethyl carbonate = 3:7).

The charge/discharge characteristics of lithium secondary batteries using the titanium-containing lithium-nickel-manganese composite oxides of Example 3 and Comparative Example 3 as the positive electrode active material are shown in Figures 16 and 17, respectively. In both Figures 16 and 17, the curves sloping upward to the right represent the charge curves (denoted by the subscript c), and the curves sloping downward to the right represent the discharge curves (denoted by the subscript d). Numbers indicate the number of cycles. Cycles 1 to 4 are not shown because they are cycles for electrochemical activation. The charge/discharge capacities of Example 3 and Comparative Example 3 are shown in Table 11 below.

From Figures 16 and 17 and Table 11, it can be seen that the lithium secondary battery of Example 3 had a larger charge/discharge capacity from the 5th cycle to the 34th cycle and smaller change in the charge/discharge curve over the cycles than the lithium secondary battery of Comparative Example 3. Furthermore, the average discharge voltage of the lithium secondary battery of Example 3 at the 5th cycle was 3.58 V, which was higher than the value (3.51 V) of the lithium secondary battery of Comparative Example 3.

Evaluation of Discharge Rate Characteristics (Example 3 and Comparative Example 3)
Next, the discharge rate characteristics under high current density were evaluated using the lithium secondary batteries of Example 3 and Comparative Example 3. Charge and discharge were performed in the same manner as in the above cycle test up to the fifth cycle, and then evaluation was performed 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 varied from 100 mA/g to 400 mA/g. Note that, since the depth of charge of the battery after the high current density discharge test evaluation deviates significantly from that in a normal constant current density test, one cycle of charge and discharge at a low current density (40 mA/g) was performed after each high current density discharge test to adjust the depth of charge.

Figures 18 and 19 and Table 12 show the discharge rate characteristics of the lithium secondary batteries of Example 3 and Comparative Example 3.

From Figures 18 and 19 and Table 12, it is clear that the lithium secondary battery of Example 3 has a larger discharge capacity at each current density and superior discharge rate characteristics compared to the lithium secondary battery of Comparative Example 3.

From the above, it can be seen that the heterometal-containing lithium-nickel-manganese composite oxide of the present invention has a unique distribution or abundance of metal ions other than lithium, and therefore has superior charge/discharge characteristics compared to those with a typical distribution and abundance of metal ions other than lithium, and is therefore suitable for use as a positive electrode material for large lithium-ion secondary batteries, such as those used in automobiles.

The lithium-nickel-manganese composite oxide of the present invention has operating voltage, initial charge/discharge capacity, and discharge rate characteristics that are equivalent to or superior to 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 (10)

General formula (1):
Li _1+x (Ni _y M _z Mn _1-y-z ) _1-x O ₂ (1)
[In the formula, M represents Mg or Ti, and x, y, and z represent 0<x<1/3, 0.150≦y≦0.350, and 0.050≦z≦0.150, respectively. However, when M is Mg, 0.150≦y≦0.250.]
and a heterometal-containing 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 crystalline phase of the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the ratio of the X-ray peak intensity, obtained by dividing the peak height of the (020) plane by the height of a single peak consisting of overlapping peaks of the (20-2) plane and the (131) plane, is 3.0 to 10.0% when 0.150≦y≦0.250 and the M is Mg, 3.0 to 14.0% when 0.150≦y≦0.250 and the M is Ti, and 3.0 to 8.0% when 0.250<y≦0.350 and the M is Ti.
(2) The sum of the average abundances of metals other than lithium in the lithium layer and the metal-other-than-lithium layer in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure (g _total ) is 0.780 to 0.850 when 0.150≦y≦0.250 and the M is Mg, 0.720 to 0.800 when 0.150≦y≦0.250 and the M is Ti, and 0.750 to 0.820 when 0.250<y≦0.350 and the M is Ti, and (3) in the hexagonal mesh structure in the metal-other-than-lithium layer in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the ratio of the metal occupancy rate other than lithium (g _4g ) at the hexagonal mesh lattice position (4g position) to the metal occupancy rate other than lithium (g _2b When y is 0.150≦y≦0.250 and M is Mg, the value (g _4g −g _2b ) obtained by subtracting y from Mg satisfies at least one of the following: when y is 0.150≦y≦0.250 and M is Ti, the value (g 4g −g 2b ) is 0.230 to 0.300; when y is 0.150≦y≦0.250 and M is Ti, the value (g 4g −g 2b ) ... is 0.250 to 0.390; and when y is 0.250<y≦0.350 and M is Ti, the value (g 4g −g 2b ) satisfies at least one of the following: The heterometal-containing lithium nickel manganese composite oxide according to claim 1, which satisfies (1) above. The heterometal-containing lithium nickel manganese composite oxide according to claim ₂ , wherein the sum (g _total ) of the average abundances of the lithium layer and the metal other than lithium in the metal other than lithium-lithium layer in the monoclinic Li ₂ MnO 3 -type layered rock salt structure is 0.780 to 0.850 when 0.150≦y≦0.250 and the M is Mg, 0.720 to 0.800 when 0.150≦y≦0.250 and the M is Ti, or 0.750 to 0.820 when 0.250<y≦0.350 and the M is Ti. The heterometal-containing lithium nickel manganese composite oxide according to claim 1, which satisfies (2) above. 5. The heterometal-containing lithium nickel manganese composite oxide according to claim 2, wherein in the hexagonal mesh structure of the metal-lithium layer other than lithium in the monoclinic Li ₂ MnO ₃ -type layered rock salt structure, the value (g _4g -g _2b ) obtained by subtracting the occupancy rate of the metal other than lithium (g _4g ) at the hexagonal mesh structure position (4g position) from the occupancy rate of the metal other than lithium (g _2b ) at the hexagonal mesh structure center position (2b position) is 0.230 to 0.300 when 0.150≦y≦0.250 and the M is Mg, 0.250 to 0.390 when 0.150≦y≦0.250 and the M is Ti, and 0.230 to 0.310 when 0.250<y≦0.350 and the M is Ti. The heterometal-containing lithium nickel manganese composite oxide according to claim 1, which satisfies (3) above. The heterometal-containing lithium nickel manganese composite oxide according to any one _of claims 1 to 6 _, which is composed of a crystalline phase of the monoclinic Li ₂ MnO ₃ type layered rock salt structure or a mixed phase of a crystalline phase of the monoclinic Li 2 MnO 3 type layered rock salt structure and a crystalline phase of a cubic rock salt structure. An electrode active material for a lithium ion secondary battery, containing the heterometal-containing lithium nickel manganese composite oxide according to any one of claims 1 to 7. A lithium ion secondary battery comprising the electrode active material for lithium ion secondary batteries according to claim 8. A method for producing the heterometal-containing lithium nickel manganese composite oxide according to any one of claims 1 to 7,
Step 1: forming a precipitate by treating a mixture of a magnesium compound or a titanium compound, a manganese compound, and a nickel compound with an alkali;
Step 2: oxidizing the precipitate to obtain a composite oxide precursor;
Step 3: heat-treating the composite oxide precursor in an oxidizing atmosphere in the presence of a lithium compound; and Step 4: heat-treating the product obtained in Step 3 in an inert atmosphere at a higher temperature than in Step 3.
A manufacturing method comprising the steps of: