Monoclinic lithium nickel manganese composite oxide containing different metals and its method of manufacture

Abstract

To provide an electrode active material having actuation electrical voltage, charge-discharge capacity and discharge rate characteristics similar to or more than existing NMC-based cathode active materials.SOLUTION: A dissimilar metal-containing lithium nickel manganese-based composite oxide including Mg and / or Ti and having a monoclinic Li2MnO3-type laminar rock salt type structure has (1) in an X-ray diffraction pattern of a crystal phase of the monoclinic Li2MnO3-type laminar rock salt type structure, a rate of X-ray peak intensity obtained by dividing a peak height of a peak of a (020) plane by a height of a single peak comprising overlapping of peaks of a (20-2) plane and a (131) plane, (2) a total (gtotal) of average existence amounts of a metal-other-than-lithium in a lithium layer and a metal-other-than-lithium / lithium layer, or (3) a value (g4g-g2b) obtained by subtracting an occupancy of the metal-other-than-lithium (g2b) at a hexagon network grating center location (2b position) from an occupancy of the metal-other-than-lithium (g4g) at a hexagon network grating constitution position (4g position), within specified ranges.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heterometal-containing monoclinic lithium nickel manganese composite oxide and a method for producing the same. [Background technology]

[0002] Lithium-ion secondary batteries are useful as secondary batteries installed in laptop computers, smartphones, etc., and are also considered important as batteries for electric vehicles and plug-in hybrid vehicles, as well as system power sources for power load leveling systems, etc., and development is underway.

[0003] 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 from 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.

[0004] Currently, the cathode active materials commonly used in large-capacity lithium-nickel-manganese-cobaltate (NMC) and lithium-nickel-oxide are the two main types of cathode active materials. Compared to NMC, lithium-nickel-oxide cathodes have a higher capacity per weight of cathode active material, but they have safety issues 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.

[0005] Both materials contain the rare and unevenly distributed cobalt element, and to mitigate the risk of unstable and rising cobalt 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 cost has been rising due to the recent battery development race, so there is a similar demand for its reduction.

[0006] 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 Li2MnO3 layered rock salt structure, exhibit excellent charge-discharge characteristics. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-179501 [Patent Document 2] International Publication No. 2019 / 235573 [Patent Document 3] Japanese Patent Publication No. 2021-017397 [Patent Document 4] International Publication No. 2018 / 169004 [Non-patent literature]

[0008] [Non-Patent Document 1] Mitsuharu Tabuchi et al., Electrochimica Acta, 210 (2016) 105-110. [Non-patent document 2] Mitsuharu Tabuchi et al., 59th Battery Symposium Abstracts 3D21, (2018) [Non-patent document 3] Mitsuharu Tabuchi, Abstracts of the 60th Battery Symposium 2A05, (2019) Summary of the Invention [Problem to be solved by the invention]

[0009] However, in Patent Document 1, it could not be said that the operating voltage, charge-discharge capacity, discharge rate characteristics, etc. were sufficient. Further, in Patent Document 2, it is described that when a manganese compound of trivalent or higher is used as a raw material in a specific amount or more and secondary firing is performed in an air atmosphere, the discharge capacity and charge-discharge cycle characteristics are excellent. However, when attempting to improve the discharge rate characteristics, it is often not preferable under the same conditions. Therefore, among heterogeneous metal-substituted lithium nickel manganese-based composite oxides, it remains unclear which materials should be selected to manufacture a secondary battery that is particularly excellent in operating voltage, charge-discharge capacity, and discharge rate characteristics.

[0010] In view of the above circumstances, an object of the present invention is to provide an electrode active material having an operating voltage, charge-discharge capacity, and discharge rate characteristics equal to or better than those of existing NMC-based positive electrode active materials.

Means for Solving the Problems

[0011] As a result of intensive studies to achieve the above object, the present inventor has found that in a lithium nickel manganese-based composite oxide containing a heterogeneous metal of magnesium or titanium, by setting the distribution or abundance of metal ions other than lithium, which consists of the heterogeneous metal, Ni, and Mn, to predetermined conditions, the above problems can be solved. Based on such findings, the present inventor has further conducted research and completed the present invention.

[0012] That is, the present invention includes the following lithium nickel manganese-based composite oxide and a method for producing the same.

[0013] Item 1. General formula (1): Li 1+x (Ni y M z Mn 1-y-z ) 1-x O2(1) [In the formula, M represents Mg and / or Ti. x, y, and z each represent 0 < x < 1 / 3, 0.150 ≤ y ≤ 0.350, 0.050 ≤ z ≤ 0.150. However, when M is Mg, it represents 0.150 ≤ y ≤ 0.250.] A heterogeneous metal-containing lithium nickel manganese composite oxide represented by [formula] and having a monoclinic Li₂MnO₃-type layered rock salt structure, comprising the following (1) to (3): (1) In the X-ray diffraction pattern of the crystal phase of the monoclinic Li₂MnO₃-type layered rock salt structure, the ratio of the X-ray peak intensity obtained by excluding the peak height of the peak of the (020) plane from the height of a single peak composed of the overlapping peaks of the (20-2) plane and the (131) plane is such that 0.150 ≤ y ≤ 0.250 and when M is Mg, it is 3.0 to 10.0%, 0.150 ≤ y ≤ 0.250 and when M is Ti, it is 3.0 to 14.0%, 0.250 < y ≤ 0.350 and when M is Ti, it is 3.0 to 8.0%. (2) The sum of the average abundances of metals other than lithium in the lithium layer and the metal-lithium layer other than lithium in the monoclinic Li₂MnO₃-type layered rock salt structure (g total ) is such that 0.150 ≤ y ≤ 0.250 and when M is Mg, it is 0.780 to 0.850, 0.150 ≤ y ≤ 0.250 and when M is Ti, it is 0.720 to 0.800, 0.250 < y ≤ 0.350 and when M is Ti, it is 0.750 to 0.820, and (3) In the hexagonal network regular structure in the metal-lithium layer other than lithium in the monoclinic Li₂MnO₃-type layered rock salt structure, the value obtained by subtracting the occupancy of the metal other than lithium at the hexagonal network lattice constituent position (4g position) (g 4g ) from the occupancy of the metal other than lithium at the hexagonal network lattice center position (2b position) (g 2b ) (g 4g - g 2b ) is such that 0.150 ≤ y ≤ 0.250 and when M is Mg, it is 0.230 to 0.300, 0.150 ≤ y ≤ 0.250 and when M is Ti, it is 0.250 to 0.390, 0.250 < y ≤ 0.350 and when M is Ti, it is 0.230 to 0.310 A heterogeneous metal-containing lithium nickel manganese composite oxide, characterized by satisfying at least one of the above.

[0014] The heterogeneous metal-containing lithium nickel manganese composite oxide according to claim 1, satisfying the above (1).

[0015] Item 3. The sum of the average abundances of metals other than lithium in the lithium layer and the metal-lithium layer other than lithium within the monoclinic Li2MnO3-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. The heterogeneous metal-containing lithium nickel manganese composite oxide according to Item 2.

[0016] Item 4. The heterogeneous metal-containing lithium nickel manganese composite oxide according to Item 1, which satisfies the condition of (2).

[0017] Item 5. In the hexagonal network regular structure within the metal-lithium layer other than lithium in the monoclinic Li2MnO3-type layered rock salt structure, the occupancy of the metal other than lithium at the hexagonal network lattice constituent position (4g position) (g 4g ) minus the occupancy of the metal other than lithium at the hexagonal network lattice center position (2b position) (g 2b ) gives a value (g 4g - g 2b ) that 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. The heterogeneous metal-containing lithium nickel manganese composite oxide according to any one of Items 2 to 4.

[0018] Item 6. The heterogeneous metal-containing lithium nickel manganese composite oxide according to Item 1, which satisfies the condition of (3).

[0019] Item 7. The heterogeneous metal-containing lithium nickel manganese composite oxide according to any one of Items 1 to 6, which is composed of the crystal phase of the monoclinic Li2MnO3-type layered rock salt structure or a mixed phase of the crystal phase of the monoclinic Li2MnO3-type layered rock salt structure and the crystal phase of the cubic rock salt structure.

[0020] Item 8. An electrode active material for a lithium ion secondary battery, comprising the different metal-containing lithium nickel manganese composite oxide according to any one of Items 1 to 7.

[0021] Item 9. A lithium ion secondary battery comprising the electrode active material for lithium ion secondary batteries according to Item 8.

[0022] Item 10. A method for producing a heterometal-containing lithium nickel manganese composite oxide according to any one of items 1 to 7, 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 under an inert atmosphere at a higher temperature than in step 3 A manufacturing method comprising the steps of: [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an electrode material that has operating voltage, charge / discharge capacity, and discharge rate characteristics equivalent to or superior to those of existing NMC-based positive electrode active materials. [Brief explanation of the drawings]

[0024] [Figure 1] (a) bc plane arrangement diagram of the crystal structure of the lithium nickel manganese composite oxide of the present invention. (b) Arrangement diagram of a metal other than lithium (TM)-lithium layer on the ab plane of the crystal structure of the lithium nickel manganese composite oxide of the present invention. [Figure 2] 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. [Figure 3]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. [Figure 4] Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Example 1 as a positive electrode active material. [Figure 5] Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Comparative Example 1 as a positive electrode active material. [Figure 6] 1 shows the discharge rate characteristics of a lithium secondary battery using the composite oxide of Example 1 as a positive electrode active material. [Figure 7] 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. [Figure 8] 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. [Figure 9] 1 is a measured (+) and calculated (solid line) X-ray diffraction pattern of the lithium nickel manganese composite oxide of Comparative Example 2 using CuKα radiation. [Figure 10] Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Example 2 as a positive electrode active material. [Figure 11] Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Comparative Example 2 as a positive electrode active material. [Figure 12] 1 shows the discharge rate characteristics of a lithium secondary battery using the composite oxide of Example 2 as a positive electrode active material. [Figure 13] 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. [Figure 14] 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. [Figure 15] 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. [Figure 16] 5 shows the charge-discharge characteristics of a lithium secondary battery using the composite oxide of Example 3 as a positive electrode active material. [Figure 17] Charging and discharging characteristics of a lithium secondary battery using the composite oxide of Comparative Example 3 as a positive electrode active material. [Figure 18]Discharge rate characteristics of a lithium secondary battery using the composite oxide of Example 3 as a positive electrode active material. [Figure 19] Discharge rate characteristics of a lithium secondary battery using the composite oxide of Comparative Example 3 as a positive electrode active material.

Mode for Carrying Out the Invention

[0025] In this specification, "containing" is a concept encompassing any of "comprise", "consist essentially of", and "consist of". Also, in this specification, when a numerical range is indicated as "A to B", it means A or more and B or less.

[0026] (1. Hetero-metal-containing lithium nickel manganese composite oxide) The hetero-metal-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 O2(1) [In the formula, M represents Mg and / or Ti. x, y, and z each represent 0 < x < 1 / 3, 0.150 ≤ y ≤ 0.350, 0.050 ≤ z ≤ 0.150. However, when M is Mg, it represents 0.150 ≤ y ≤ 0.250.] It is represented by.

[0027] The hetero-metal-containing lithium nickel manganese composite oxide of the present invention is a hetero-metal-containing lithium nickel manganese composite oxide having a monoclinic Li2MnO3-type layered rock salt structure.

[0028] The monoclinic Li2MnO3-type layered rock salt structure has a crystal structure of a space group represented by the following spatial formula (a) described in P. Strobel et al., J. Solid State Chem., 75, 90 - 98, (1988).

[0029]

Number

[0030] Here, in the first aspect (requirement (3)) of the heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention, in the hexagonal network regular structure within the metal-lithium layer other than lithium in the monoclinic Li2MnO3-type layered rock salt structure, the occupancy rate of the metal other than lithium at the hexagonal network lattice constituent position (g 4g ) minus the occupancy rate of the metal other than lithium at the center position of the hexagonal network lattice (g 2b ), the value (g 4g - g 2b ) is 0.150 ≦ y ≦ 0.250 and 0.230 to 0.300 when M is Mg, 0.150 ≦ y ≦ 0.250 and 0.250 to 0.390 when M is Ti, and 0.250 < y ≦ 0.350 and 0.230 to 0.310 when M is Ti. The heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention in this first aspect has a distribution of metal (TM) ions other than lithium composed of Mg, Ti, Ni, and Mn different from that of known Li2MnO3, as shown in FIG. 1.

[0031] FIG. 1(a) shows the entire layered rock salt structure, and FIG. 1(b) shows the cation arrangement within the metal-lithium layer (TM-Li layer) other than lithium obtained by rotating the metal-lithium layer (TM-Li layer) other than lithium in FIG. 1(a) by 90°. In FIG. 1(a), regarding the point where the metal-lithium layer (TM-Li layer) other than lithium and the lithium layer (Li layer) are alternately stacked through the oxide ion (large gray circle) layer, it is the same as the hexagonal layered rock salt crystal structure (space group represented by the space formula in (b) below) of a conventional NMC positive electrode, etc., but the cation distribution within the lithium layer and the metal-lithium layer other than lithium is different from that of the existing positive electrode.

[0032]

Number

[0033] In the hexagonal-layered rock salt-type crystal structure of a conventional NMC cathode or the like, the cation lattice positions in the lithium layer and the metal-lithium layer other than lithium are each of one type. However, in the monoclinic-layered rock salt-type crystal structure of the present invention in the first aspect, there are two types of cation lattice positions in the lithium layer and the metal layer-lithium layer other than lithium.

[0034] In the lithium layer of FIG. 1(a), the lattice positions correspond to the 2c and 4h positions, and in the metal-lithium layer (TM-Li layer) other than lithium, the lattice positions correspond to the 4g and 2b positions as shown in FIG. 1(b). The heterogeneous metal-containing lithium nickel manganese-based composite oxide of the present invention in the first aspect is characterized by the distribution of metal ions other than lithium in this TM-Li layer.

[0035] As shown in FIG. 1(b), the 4g position corresponds to the hexagonal mesh lattice configuration position, and the 2b position corresponds to the hexagonal mesh lattice center position. In the ideal Li2MnO3 structure, metal ions other than lithium enter only the 4g position, and lithium ions enter the 2b position. However, actually, metal ions other than lithium can occupy both lattice positions.

[0036] In the first aspect of the present invention, the difference (g 4g ) between the occupancy rate (g 2b ) of metal ions other than lithium at the 4g position and the occupancy rate (g 4g ) of metal ions other than lithium at the 2b position obtained by the X-ray Rietveld method is small. The value of (g 2b ) is 0.150 ≦ y ≦ 0.250 and when M is Mg, it is 0.230 to 0.300, preferably 0.235 to 0.280. The value of (g 4g ) is 0.150 ≦ y ≦ 0.250 and when M is Ti, it is 0.250 to 0.390, preferably 0.300 to 0.380. The value of (g 2b ) is 0.250 < y ≦ 0.350 and when M is Ti, it is from 0.230 to 0.310, preferably 0.235 to 0.290. The value of (g 4g ) is 0.250 < y ≦ 0.350 and when M is Ti, it is from 0.230 to 0.310, preferably 0.235 to 0.290. The value of (g 2b ) is 0.250 < y ≦ 0.350 and when M is Ti, it is from 0.230 to 0.310, preferably 0.235 to 0.290. The value of (g 4g ) is 0.250 < y ≦ 0.350 and when M is Ti, it is from 0.230 to 0.310, preferably 0.235 to 0.290. The value of (g 2b ) is 0. S. 0 < y ≦ 0.350 and when M is Ti, it is from 0.230 to 0.310, preferably 0.235 to 0.290. The value of (g 4g ) is 0.250 < y ≦ 0.350 and when M is Ti, it is from 0.230 to 0.310, preferably 0.235 to 0.290. The value of (g 4g -g2b ) By setting this range, a trivalent or higher-valence Mn source is not required, and an inexpensive divalent Mn source can be utilized, which is industrially advantageous. In addition, the generation of electrochemically inert Li2MnO3-rich components is suppressed, and it is easy to obtain a sample with a high charge-discharge capacity both initially and after charge-discharge cycles and excellent high discharge rate characteristics.

[0037] Further, in the monoclinic Li2MnO3-type layered rock salt-type structure, metals other than lithium exist at the 2c and 4h positions within the lithium layer, and metals other than lithium also exist at the 4g and 2b positions within the metal-lithium layer other than lithium as described above. The amount of metal other than lithium per composition formula (g total ) 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 metal-lithium layer other than lithium ((2g 4g + g 2b ) / 3). Setting this value within a predetermined range is also effective for improving charge-discharge characteristics (particularly the charge-discharge capacity both initially and after charge-discharge cycles, and the discharge rate characteristics). On the other hand, this value increases as the valence and content of the constituent heterogeneous metals decrease, so the optimal value varies depending on the heterogeneous metal species and its content. Specifically, in the heterogeneous metal-containing lithium nickel manganese-based composite oxide of the present invention in the second aspect (requirement (2)), the g total value is 0.150 ≦ y ≦ 0.250 and when M is Mg, it is 0.780 to 0.850, preferably 0.785 to 0.830. The g total value is 0.150 ≦ y ≦ 0.250 and when M is Ti, it is 0.720 to 0.800, preferably 0.725 to 0.780. The g total value is 0.250 < y ≦ 0.350 and when M is Ti, it is 0.750 to 0.820, preferably 0.755 to 0.800. total By setting the g value within this range, the generation of electrochemically inert Li2MnO3-rich components is suppressed, and since the lithium content per composition formula is sufficiently large, it is easy to obtain a sample with a high charge-discharge capacity both initially and after charge-discharge cycles and excellent high discharge rate characteristics.

[0038] In addition, the heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention preferably has the ratio of X-ray peak intensity obtained by dividing the peak height of the (020) plane peak caused by the hexagonal mesh structure observed around 2θ = 20° in the X-ray diffraction pattern using CuKα rays by the height of a single peak composed of the overlapping peaks of the (20-2) plane and (131) plane peaks observed around 2θ = 45° as low as possible. Since this ratio of X-ray peak intensity tends to increase as the valence and content of the heterogeneous metal decrease, the optimal value varies depending on the heterogeneous metal species and its content. Therefore, in the heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention in the third aspect (requirement (1)), this ratio of X-ray peak intensity is 0.150 ≦ y ≦ 0.250 and 10.0% or less, preferably 9.0% or less when M is Mg. This ratio of X-ray peak intensity is 0.150 ≦ y ≦ 0.250 and 14.0% or less, preferably 13.5% or less when M is Ti. This ratio of X-ray peak intensity is 0.250 < y ≦ 0.350 and 8.0% or less, preferably 7.5% or less when M is Ti. By setting the ratio within this range, the generation of electrochemically inactive Li2MnO3 components can be suppressed, and a sample having desired initial and charge-discharge capacities after charge-discharge cycles and high discharge rate characteristics can be easily obtained. Note that the lower limit value of this ratio of X-ray peak intensity is not particularly limited, and for example, it is preferably 3.0%.

[0039] In the general formula (1), x represents the excess lithium amount, specifically, 0 < x < 1 / 3. By setting the value of x within this range, it is easy to introduce lithium into the structure without using lithium more than necessary, and it is difficult to remain as an impurity phase in the product, which is advantageous in terms of cost. Further, x is preferably 0.05 to 0.30.

[0040] The heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention can be obtained, for example, by producing an oxide represented by a specific composition formula using the coprecipitation-calcination method described later. By adopting this production method, metal ions other than lithium have an occupancy rate (g4g ) and the difference (g 2b ) in the metal ion occupancy other than lithium at the 2b position, the amount of metal other than lithium per composition formula (g 4g -g 2b ), and it is considered that there is an effect of reducing the ratio of the X-ray peak intensity.

[0041] In addition, for example, when producing an oxide represented by a specific composition formula using the coprecipitation-firing method described later, a heterogeneous metal-containing lithium nickel manganese-based composite oxide that satisfies all of the above requirements (1) to (3) is likely to be generated. Specifically, in the hexagonal network regular structure within the metal-lithium layer other than lithium in the monoclinic Li2MnO3-type layered rock salt structure, the occupancy of the metal other than lithium at the hexagonal network lattice constituent position (g 4g ) minus the occupancy of the metal other than lithium at the center position of the hexagonal network lattice (g 2b ), the value (g 4g -g 2b ) is 0.150 ≦ y ≦ 0.250 and when M is Mg, it is 0.230 to 0.300, 0.150 ≦ y ≦ 0.250 and when M is Ti, it is 0.250 to 0.390, 0.250 < y ≦ 0.350 and when M is Ti, it is 0.230 to​​​) is 0.780 - 0.850 when 0.150 ≤ y ≤ 0.250 and M is Mg, 0.720 - 0.800 when 0.150 ≤ y ≤ 0.250 and M is Ti, and 0.750 - 0.820 when 0.250 < y ≤ 0.350 and M is Ti (requirement (2)). A heterogeneous metal-containing lithium nickel manganese composite oxide is likely to be formed.

[0042] In addition, for the stabilization of the metal ion distribution other than lithium, the amount of nickel ions y per total metal amount other than lithium is 0.150 ≤ y ≤ 0.350. It can also be 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, for the stabilization of the metal ion distribution other than lithium, the amount of nickel ions y per total metal amount other than lithium is 0.150 ≤ y ≤ 0.250, preferably 0.175 ≤ y ≤ 0.225. By setting y within this range, while sufficiently maintaining the discharge potential increase effect of nickel ions, the amount of Mn in the composition formula is not excessive, the metal ion distribution other than lithium in the metal - lithium layer other than lithium can be stabilized, and as a result, the charge - discharge capacity can be improved by ensuring an adequate amount of lithium ions in the composition formula.

[0043] The heterogeneous metal-containing lithium nickel manganese composite oxide of the present invention is preferably composed of the crystal phase of the monoclinic Li2MnO3-type layered rock salt structure or a mixed phase of the crystal phase of the monoclinic Li2MnO3-type layered rock salt structure and the crystal phase of the cubic rock salt structure.

[0044] In other words, the heterogeneous metal-containing lithium nickel manganese composite oxide preferably contains the crystal phase of the above-described monoclinic Li2MnO3-type layered rock salt structure. Of course, it is also preferable that it is a mixed phase containing other rock salt-type crystal structures. Specifically, it is also preferable that it is a mixed phase further containing the crystal phase of the cubic rock salt structure represented by the space group of the following formula (c).

[0045]

Number

[0046] The ratio of the monoclinic Li2MnO3-type layered rock-salt structure crystal phase to the cubic rock-salt structure crystal phase is preferably in the range of approximately 100:0 to 10:90 (mass ratio) of monoclinic Li2MnO3-type layered rock-salt structure crystal phase:cubic rock-salt structure crystal phase. The different metal-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 crystal 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 Li2MnO3-type layered rock-salt structure is a single phase or the monoclinic Li2MnO3-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 whose peaks can be confirmed in the X-ray diffraction pattern is 100 mass %).

[0047] (2. Electrode active material for lithium-ion secondary batteries and lithium-ion secondary batteries) 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. Lithium-ion secondary batteries can also be manufactured by conventional methods using the heterometal-containing lithium-nickel-manganese composite oxide of the present invention as the positive electrode active material. Specifically, lithium-ion secondary batteries can be assembled by conventional methods using the heterometal-containing lithium-nickel-manganese composite oxide of the present invention as the positive electrode active material, known materials such as lithium metal, lithium titanate, silicon, silicon oxide, and carbon-based materials (graphite-based materials and non-graphitizable materials) as the negative electrode active material, and known organic electrolyte solutions such as lithium perchlorate and lithium salts such as LiPF6 dissolved in solvents such as ethylene carbonate and dimethyl carbonate, polymer electrolytes, sulfide solid electrolytes, and other known battery components.

[0048] (3. Method for producing 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 adjusting the alkalinity of a mixture of a magnesium compound and / or a titanium compound, a manganese compound, and a nickel compound to form a precipitate; 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.

[0049] (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.

[0050] The magnesium compound, titanium compound, manganese compound, and nickel compound function as the magnesium source, titanium source, manganese source, and nickel source of the heterometal-containing lithium-nickel-manganese composite oxide, respectively. A wide variety of known metal salts of magnesium, titanium, manganese, and nickel can be used, and there are 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(VII), manganese(III) acetate, manganese(III) acetylacetate, etc. may also be used as a high-valent Mn source. Other examples include magnesium metal, titanium metal, manganese metal, or nickel metal, and 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 each be used alone or in combination.

[0051] 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 target heterometal-containing lithium nickel manganese composite oxide.

[0052] As described above, the manufacturing method of the present invention is likely to produce a heterogeneous metal-containing lithium nickel manganese composite oxide that satisfies all of the above requirements (1) to (3). Specifically, in a hexagonal mesh structure within a metal other than lithium-lithium layer within a monoclinic Li2MnO3-type layered rock salt structure, the occupancy rate (g 4g ) to determine the metal occupancy rate (g 2b ) minus the value (g 4g -g 2b) 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)). The ratio of the X-ray peak intensity obtained by dividing the peak height of the (020) plane peak observed near 2θ = 20° in the X-ray diffraction pattern of the crystal phase of the monoclinic Li2MnO3-type layered rock salt structure by the height of a single peak composed of the overlapping peaks of the (20-2) plane and (131) plane peaks observed near 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)). The sum of the average abundances of metals other than lithium in the lithium layer and the metal-lithium layer other than lithium in the monoclinic Li2MnO3-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)). A heterogeneous metal-containing lithium nickel manganese composite oxide is likely to be formed. <0000​​​​​​The magnesium compound, titanium compound, manganese compound, and nickel compound are preferably a mixture containing the magnesium compound and / or titanium compound, the manganese compound, and the nickel compound, more preferably dissolved in an appropriate solvent to form a mixed solution of the magnesium compound and / or titanium compound, the manganese compound, and the nickel compound, and even more preferably dissolved in water to form a mixed aqueous solution of the magnesium compound and / or titanium compound, the manganese compound, and the nickel compound. There are no particular limitations on the concentration of the mixed aqueous solution, and for example, the total concentration of the magnesium compound, titanium compound, manganese compound, and nickel compound is preferably 0.01 to 5 mol / L, more preferably 0.1 to 2.0 mol / L.

[0055] A mixture containing a magnesium compound and / or a 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 a titanium compound, the manganese compound, and the nickel compound alkaline.

[0056] The pH of the alkali treatment of 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 may be appropriately set in consideration of 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 about 14.

[0057] There are no particular limitations on the specific method of operation for the alkali treatment. For example, a method can be used in which a mixture containing a magnesium compound and / or a titanium compound, a manganese compound, and a nickel compound is gradually added to an alkaline aqueous solution. When using such a method, it is preferable to use, for example, a liquid pump to drop the mixture (preferably a mixed solution, more preferably a mixed aqueous solution) over a period of preferably 1 to 10 hours, more preferably 2 to 5 hours. By using such a method, a uniform precipitate can be obtained.

[0058] The alkaline substance used in the alkaline treatment is not particularly limited, and examples thereof include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, lithium hydroxide, and lithium hydroxide monohydrate, as well as ammonia, etc. 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.

[0059] 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. Here, the alcohol used 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 a precipitate at temperatures below 0°C. Furthermore, by adding alcohol, the alcohol functions as a reducing agent, making it easier to form a precipitate using potassium permanganate(VII), which is one of the high-valent Mn sources.

[0060] The amount of alcohol used in the water-alcohol mixed solvent may be appropriately set depending on the target precipitation temperature. For example, the amount of alcohol used is preferably 10 to 50 parts by mass, and more preferably 20 to 40 parts by mass, per 100 parts by mass of water.

[0061] Considering that heat of neutralization is generated during precipitation, it is preferable to control the temperature during precipitation using a thermostatic bath, etc. The set temperature during the alkali treatment is preferably −20 to 80°C, and more preferably −10 to 60°C.

[0062] (3.2.Process 2) In step 2, the precipitate obtained in step 1 is oxidized to obtain a composite oxide precursor.

[0063] In step 2, it is preferable to subject the reaction system containing the precipitate to an oxidation treatment. The oxidation treatment can be carried out by blowing air or oxygen into the reaction system at a temperature preferably from 0 to 150°C, more preferably from 10 to 100°C, for preferably 0.5 to 7 days, more preferably 1 to 4 days.

[0064] In order to obtain a uniform sample, the oxidation treatment is preferably carried out under wet conditions, and a specific example of the wet conditions is bubbling treatment.

[0065] A composite oxide precursor can be obtained through the above oxidation treatment. The composite oxide precursor may be used as is in the next step 3, or may be purified by washing with distilled water or the like, removing excess alkaline components and residual raw materials, and filtering to obtain a composite oxide precursor, which may then be used in step 3.

[0066] (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.

[0067] The lithium compound to be used is not particularly limited, and for example, a lithium salt can be used. More specifically, lithium carbonate, lithium hydroxide, lithium hydroxide hydrate, lithium nitrate, lithium acetate, etc. can be exemplified.

[0068] 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 the value obtained by assuming yNiO-zMO-(1-yz)Li2MnO3 when the valence of different metals is divalent (when M is Mg), nickel is divalent, and manganese is tetravalent in (Li / (Ni+M+Mn) (molar ratio)). 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 x 0 + 0.70 x 2 = 1.40 By using this, 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) can be set to a value in excess of the target composition, such as 2.00, and the excess lithium salt can be removed after the heat treatment by water washing, filtration, drying, etc.

[0069] The composite oxide precursor and the lithium compound may be dry-mixed and the resulting mixture may be subjected to heat treatment. However, 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.

[0070] 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, mix, and form a slurry.

[0071] The obtained slurry is preferably dried before heat treatment to obtain a dry mixture. The drying conditions are not particularly limited. For example, it is preferable to dry slowly at a temperature of 40 to 60°C, since this makes it easier to prevent separation of the lithium salt and precipitate, which have different specific gravities.

[0072] Thereafter, 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. When the dried mixture is heat-treated, it is preferable to perform a pulverization treatment before the heat treatment. The conditions for the pulverization treatment are not particularly limited, and it is sufficient that the pulverized product does not contain coarse particles and has a uniform color tone.

[0073] In step 3, the heat treatment is carried out in an oxidizing atmosphere. Examples of the oxidizing atmosphere include air and oxygen.

[0074] The temperature condition for the heat treatment is preferably 400 to 800° C., more preferably 500 to 700° C. The heat treatment time is, for example, preferably 1 to 30 hours, more preferably 3 to 20 hours.

[0075] (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.

[0076] 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.

[0077] The heat treatment in step 4 is carried out in an inert atmosphere. The inert atmosphere is not particularly limited as long as it is an environment that suppresses oxidation at high temperatures, and examples thereof include an environment in nitrogen or argon.

[0078] 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 effect cannot be obtained, and therefore a sample with excellent charge-discharge cycle characteristics cannot be obtained.

[0079] The specific temperature conditions for the heat treatment in step 4 are preferably 800 to 1000° C., more preferably 850 to 950° C. The heat treatment time is, for example, preferably 1 to 30 hours, more preferably 3 to 20 hours.

[0080] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention. [Example]

[0081] Hereinafter, the embodiments of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0082] 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 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 solution was placed in a titanium beaker and, with stirring, placed in a thermostatic bath maintained at +20°C. The Ni-Mg-Mn aqueous solution was then slowly added dropwise to the sodium hydroxide solution over 2–3 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, subjecting it to wet oxidation treatment, thereby aging the precipitate and obtaining the desired precursor (Step 2).

[0083] The precursor was washed with distilled water and filtered. The resulting material was mixed with 1.00 times (molar ratio) lithium carbonate (18.47 g; (Li / (Ni+Mg+Mn) (molar ratio) 2.00)) and 200 mL of distilled water, and mixed in a mixer to produce a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) dish and dried at 50°C for 2 days.

[0084] 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, then placed in the 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.

[0085] (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.

[0086] 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 Li2MnO3 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 (virtual atom Ni) at each lattice site 0.20 Mg 0.10 Mn 0.70 The occupancy rate was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 1 below.

[0087] X-ray diffraction measurement (Comparative Example 1) Figure 3 shows a comparison 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 Li2MnO3 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 = 4.9447(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 metals other than lithium (virtual atoms Ni 0.20 Mg 0.10 Mn 0.70 The occupancy rate was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 1 below.

[0088] [Table 1]

[0089] As shown in Table 1, the composite oxide of Example 1 has a difference g between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position). 4g -g 2b The ratio I of the height of the single peak consisting of the peak of the (020) plane near 2θ=20° and the peak of the (20-2) plane and the peak of the (131) plane near 2θ=45° is 0.244, which is clearly within the range of the present invention. 020 / I 20-2,131 The average metal content in the lithium layer ((2g)) was 7.58%, which is clearly within the range of the present invention. 4h +g 2c ) / 3) and the average metal content in the metal-lithium layer ((2g 4g +g 2b ) / 3) is the sum of the amount of metals other than lithium per formula (g total ) is 0.799, which is clearly within the scope of the present invention.

[0090] As for the composite oxide of Comparative Example 1, as shown in Table 1, the difference g between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position) 4g -g 2b is 0.355, which is clearly outside the scope of the present invention. In addition, the height ratio I of the single peak consisting 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 020 / I 20-2,131 The average metal content in the lithium layer ((2g)) was 10.95%, which is clearly outside the scope of the present invention. 4h +g 2c ) / 3) and the average metal content in the metal-lithium layer ((2g 4g +g 2b The amount of metal per formula (g) is defined as the sum of total ) is 0.772, which is clearly outside the scope of the present invention. Therefore, it is clear that step 4 needs to be carried out under an inert atmosphere.

[0091] 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.

[0092] [Table 2]

[0093] 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 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 and a current density of 40 mA / g starting from the charge start. A stepwise charging method was applied up to the fourth cycle for electrochemical activation. From cycles 1 to 4, the charge capacity was increased from 80 mAh / g by 40 mAh / g, and the battery was discharged to 2.0 V at each cycle. 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 at a constant current 29 times within the potential range of 2.0-4.6 V.

[0094] 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. Note that 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.

[0095] [Table 3]

[0096] 4 and 5 and Table 3 show that the lithium 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 than the lithium secondary battery of Comparative Example 1. 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.

[0097] 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 until the fifth cycle, and then evaluation was performed by fixing the current density during charge at 40 mA / g and varying the discharge current density from 100 mA / g to 400 mA / g in the potential range of 2.0 to 4.6 V. 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.

[0098] 6 to 7 and Table 4 show the discharge rate characteristics of the lithium secondary batteries of Example 1 and Comparative Example 1.

[0099] [Table 4]

[0100] 6 to 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 is superior in discharge rate characteristics compared to the lithium secondary battery of Comparative Example 1.

[0101] Example 2 14.54 g of nickel(II) nitrate hexahydrate, 20.00 g of 30% titanium(IV) sulfate aqueous 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 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 solution was placed in a titanium beaker and, with stirring, placed in a thermostatic bath maintained at +20°C. The Ni-Ti-Mn aqueous solution was then slowly added dropwise to the sodium hydroxide solution over 2–3 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, subjecting it to wet oxidation treatment, thereby aging the precipitate and obtaining the desired precursor (Step 2).

[0102] The precursor was washed with distilled water and filtered. The resulting material was mixed with 1.00 times (molar ratio) lithium carbonate (18.47 g; Li / (Ni+Ti+Mn) (molar ratio) 2.00) and 200 mL of distilled water, and mixed in a mixer to produce a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) dish and dried at 50°C for 2 days.

[0103] 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, then placed in the 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.

[0104] (Comparative Example 2) In the secondary firing in step 4, the inert atmosphere of nitrogen was changed to air, and the same preparation as in Example 2 was carried out to obtain a titanium-containing lithium nickel manganese composite oxide.

[0105] X-ray diffraction measurement (Example 2) A comparison of the measured pattern (+) of Example 2 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern (solid line) obtained using a monoclinic Li2MnO3 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 metals other than lithium (virtual atoms Ni 0.20 Ti 0.10 Mn 0.70 The occupancy rate was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 5 below.

[0106] X-ray diffraction measurement (Comparative Example 2) Figure 9 shows a comparison 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 Li2MnO3 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 = 4.9443(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 metals other than lithium (virtual atoms Ni 0.20 Ti 0.10 Mn 0.70 The occupancy rate was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 5 below.

[0107] [Table 5]

[0108] As shown in Table 5, the composite oxide of Example 2 has a difference g between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position). 4g -g 2b The ratio I of the height of the single peak consisting of the peak of the (020) plane near 2θ=20° and the peak of the (20-2) plane and the peak of the (131) plane near 2θ=45° is 0.376, which is clearly within the scope of the present invention. 020 / I 20-2,131 The average metal content in the lithium layer ((2g)) was 13.32%, which is clearly within the range of the present invention. 4h +g 2c ) / 3) and the average metal content in the metal-lithium layer ((2g 4g +g 2b ) / 3) is the sum of the amount of metals other than lithium per formula (g total ) is 0.736, which is clearly within the scope of the present invention.

[0109] As for the composite oxide of Comparative Example 2, as shown in Table 5, the difference g between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position) 4g -g 2b The ratio I of the height of the single peak consisting of the peak of the (020) plane near 2θ=20° and the overlap of the peaks of the (20-2) and (131) planes near 2θ=45° is 0.404, which is clearly outside the scope of the present invention. 020 / I 20-2,131 The average metal content in the lithium layer ((2g)) was 15.25%, which is clearly outside the scope of the present invention. 4h +g 2c ) / 3) and the average metal content in the metal-lithium layer ((2g 4g +g 2b The amount of metal per formula (g) is defined as the sum of total ) is 0.713, which is clearly outside the scope of the present invention. Therefore, it is clear that step 4 needs to be carried out under an inert atmosphere.

[0110] 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.

[0111] [Table 6]

[0112] 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.

[0113] 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 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. Note that 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.

[0114] [Table 7]

[0115] 10 and 11 and Table 7 show that the lithium secondary battery of Example 2 had a larger charge / discharge capacity at the 5th cycle and showed almost the same charge / discharge capacity at the 14th cycle, and showed little change in the shape of the charge / discharge curve over the cycles, compared to the lithium secondary battery of Comparative Example 2. 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.

[0116] Discharge rate characteristic evaluation 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.

[0117] 12 and 13 and Table 8 show the discharge rate characteristics of the lithium secondary batteries of Example 2 and Comparative Example 2.

[0118] [Table 8]

[0119] 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 is superior in discharge rate characteristics compared to the lithium secondary battery of Comparative Example 2.

[0120] 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 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 solution was placed in a titanium beaker and, with stirring, placed in a thermostatic bath maintained at +50°C. The Ni-Ti-Mn aqueous solution was then slowly added dropwise to the sodium hydroxide solution over 2–3 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, subjecting it to wet oxidation treatment, thereby aging the precipitate and obtaining the desired precursor (Step 2).

[0121] The precursor was washed with distilled water and filtered. The resulting material was mixed with 1.00 times (molar ratio) lithium carbonate (18.47 g; Li / (Ni+Ti+Mn) (molar ratio) 2.00) and 200 mL of distilled water, and mixed in a mixer to produce a uniform slurry. The mixture was then transferred to a polytetrafluoroethylene (PTFE) dish and dried at 50°C for 2 days.

[0122] 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, then placed in the 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.

[0123] (Comparative Example 3) In the secondary firing in step 4, the inert atmosphere of nitrogen was changed to air, and the same preparation as in Example 3 was carried out to obtain a titanium-containing lithium nickel manganese composite oxide.

[0124] X-ray diffraction measurement (Example 3) A comparison of the measured pattern (+) of Example 3 obtained using the X-ray Rietveld analysis software RIETAN-FP with the calculated pattern (solid line) obtained using a monoclinic Li2MnO3 unit cell is shown in Figure 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 metals other than lithium (virtual atoms Ni 0.30 Ti 0.10 Mn 0.60 The occupancy rate was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 9 below.

[0125] 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 Li2MnO3 unit cell is shown in Figure 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 metals other than lithium (virtual atoms Ni 0.30 Ti 0.10 Mn 0.60 The occupancy rate was calculated assuming that the isotropic thermal vibration parameter B was 1, as shown in Table 9 below.

[0126] [Table 9]

[0127] As shown in Table 9, the composite oxide of Example 3 has a difference g between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position). 4g -g 2b The ratio I of the height of the single peak consisting of the peak of the (020) plane near 2θ=20° and the peak of the (20-2) plane and the peak of the (131) plane near 2θ=45° is 0.273, which is clearly within the scope of the present invention. 020 / I 20-2,131 The average metal content in the lithium layer ((2g)) was 6.074%, which is clearly within the range of the present invention. 4h +g 2c ) / 3) and the average metal content in the metal-lithium layer ((2g 4g +g 2b ) / 3) is the sum of the amount of metals other than lithium per formula (g total ) is 0.792, which is clearly within the scope of the present invention.

[0128] As for the composite oxide of Comparative Example 3, as shown in Table 9, the difference g between the occupancy rate of the hexagonal network configuration position (4g position) and the occupancy rate of the hexagonal network center position (2b position) 4g -g 2b is 0.312, which is clearly outside the scope of the present invention. The ratio I of the height of the single peak consisting of the peak of the (020) plane near 2θ=20° and the overlapping peaks of the (20-2) and (131) planes near 2θ=45° 020 / I 20-2,131 The average metal content in the lithium layer ((2g)) is 8.901%, which is clearly outside the scope of the present invention. 4h +g 2c ) / 3) and the average metal content in the metal-lithium layer ((2g 4g +g 2b The amount of metal per formula (g) is defined as the sum of total ) is 0.744, which is clearly outside the scope of the present invention. Therefore, it is clear that step 4 needs to be carried out under an inert atmosphere.

[0129] 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 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 3 falls within the range of the composition formula of the present invention.

[0130] [Table 10]

[0131] 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 produced, batteries were produced, and charge / discharge test conditions were set in the same manner as in Example 1, followed by a charge / discharge test. The electrolyte used was prepared by dissolving 1.5MLiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio of ethylene carbonate:dimethyl carbonate = 3:7).

[0132] 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 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. Note that 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.

[0133] [Table 11]

[0134] 16 and 17 and Table 11 show that the lithium secondary battery of Example 3 had 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 secondary battery of Comparative Example 3. 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.

[0135] Discharge rate characteristic evaluation (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 by fixing the current density during charge at 40 mA / g and varying the discharge current density from 100 mA / g to 400 mA / g in the potential range of 2.0 to 4.6 V. 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.

[0136] 18 to 19 and Table 12 show the discharge rate characteristics of the lithium secondary batteries of Example 3 and Comparative Example 3.

[0137] [Table 12]

[0138] 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 is superior in discharge rate characteristics compared to the lithium secondary battery of Comparative Example 3.

[0139] From the above, it is considered that the heterometal-containing lithium nickel manganese-based 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 having a normal distribution and abundance of metal ions other than lithium, and can be suitably used as a positive electrode material for large lithium ion secondary batteries for use in vehicles, etc. [Industrial Applicability]

[0140] The lithium nickel manganese composite oxide of the present invention has an 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, and is therefore suitable for use in batteries for electric vehicles or plug-in hybrid vehicles, stationary storage batteries, and the like.

Claims

1. General formula (1): Li １＋ｘ (N 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 monoclinic Li ２ MnO ３ A heterometal-containing lithium nickel manganese composite oxide having a layered rock salt structure, comprising the following (1) to (3): (1) The monoclinic Li ２ MnO ３ In the X-ray diffraction pattern of the crystalline phase of the layered rock salt structure, the ratio of the X-ray peak intensity, which is 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 monoclinic Li ２ MnO ３ The sum of the average abundance of lithium layers and metals other than lithium in the lithium layers in the 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; and (3) The monoclinic Li ２ MnO ３ In the hexagonal mesh structure of the metal other than lithium in the layered rock salt structure - lithium layer, the occupancy rate of the metal other than lithium at the hexagonal mesh lattice position (4g position) (g ４ｇ ) to the hexagonal mesh lattice central position (2b position) metal occupancy rate other than lithium (g ２ｂ ) minus the value (g ４ｇ -g ２ｂ ) 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. A heterometal-containing lithium nickel manganese composite oxide, characterized by satisfying at least one of the above requirements.

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

3. The monoclinic Li ２ MnO ３ The sum of the average abundance of lithium layers and metals other than lithium in the lithium layers in the layered rock salt structure (g ｔｏｔａｌ ) is 0.780 to 0.850 when 0.150≦y≦0.250 and said M is Mg, is 0.720 to 0.800 when 0.150≦y≦0.250 and said M is Ti, and is 0.750 to 0.820 when 0.250<y≦0.350 and said M is Ti. The heterometal-containing lithium nickel manganese-based composite oxide according to claim 2.

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

5. The monoclinic Li ２ MnO ３ In the hexagonal mesh structure of the metal other than lithium in the layered rock salt structure - lithium layer, the occupancy rate of the metal other than lithium at the hexagonal mesh lattice position (4g position) (g ４ｇ ) to the hexagonal mesh lattice central position (2b position) metal occupancy rate other than lithium (g ２ｂ ) minus the value (g ４ｇ -g ２ｂ ) is 0.230 to 0.300 when 0.150≦y≦0.250 and the M is Mg, is 0.250 to 0.390 when 0.150≦y≦0.250 and the M is Ti, and is 0.250 to 0.390 when 0.250<y≦0.350 and the M is Ti. The heterometal-containing lithium nickel manganese-based composite oxide according to any one of claims 2 to 4.

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

7. The monoclinic Li ２ MnO ３ The layered rock salt structure crystal phase, or the monoclinic Li ２ MnO ３ 7. The heterometal-containing lithium nickel manganese composite oxide according to claim 1, which is composed of a mixed phase of a crystalline phase having a layered rock salt structure and a crystalline phase having a cubic rock salt structure.

8. An electrode active material for a lithium ion secondary battery, comprising the heterometal-containing lithium nickel manganese composite oxide according to any one of claims 1 to 7.

9. A lithium ion secondary battery comprising the electrode active material for lithium ion secondary batteries according to claim 8.

10. 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:

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