JP7133215B2 - Nickel-manganese composite oxide and method for producing the same - Google Patents

Description

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

Lithium-ion secondary batteries developed in Japan are being put to practical use not only as power sources for small consumer devices such as laptop computers and mobile phones, but also as power load leveling devices for electric vehicles and power plants. There is an urgent need to respond to The positive electrode active material is the most costly among the lithium ion components, and is also important in determining the capacity. Lithium cobaltate was the first material to be put into practical use as a positive electrode active material, but because cobalt resources are scarce and are unevenly distributed in politically unstable countries, it tends to be avoided for large batteries. Lithium nickelate and lithium manganate have been proposed as alternative cathode materials. Low discharge capacity is a problem, and the development of alternative materials to solve these problems is expected.

A 4V-class nickel-manganese composite oxide represented by LiNi _1/2 Mn _1/2 O ₂ was proposed in 2001 as a candidate for such an alternative material (see, for example, Non-Patent Document 1). This material belongs to NiO _{- Li2MnO3} solid solution, corresponding to 0.5NiO _{- 0.5Li2MnO3} composition. According to Non-Patent Document 1, this material is safer than lithium cobalt oxide, has stable cycle characteristics even at high charging potentials up to 4.6 V, and has a hexagonal layer structure with lattice constants a = 2.89 Å and c = 14.30 Å. It is known to consist of only one rock-salt crystal phase. The problem with this positive electrode active material is that many transition metal ions enter the lithium layer. There is a background to the development of positive electrode materials. A large number of patent applications have been filed regarding this NMC positive electrode (see Patent Document 1, for example). Since cobalt is used for the NMC positive electrode after all, there is a problem of low chemical stability during charging, and such low chemical stability affects the safety of the battery and the cycle characteristics when the high upper limit potential is set. However, the need for cobalt-free cathode materials continues.

Electrochemical and Solid-State Letters, 4, A191-A194, (2001).

JP 2015-037067 A

By the way, in the nickel-manganese composite oxide described above, when lithium is excessive, a uniform and single layered rock salt type crystal phase is likely to be obtained, and although the capacity and cycle characteristics are excellent, a large amount of an expensive lithium source is used. Therefore, the amount of lithium is required to be the same number of moles as the transition metal. However, in this case, it is difficult to improve capacity and cycle characteristics.

In view of the above circumstances, the present invention provides a positive electrode active material excellent in capacity and cycle characteristics without using cobalt, which is expensive and unevenly distributed as a resource, and without using an excessive amount of lithium. The object is to obtain a composite oxide useful as

The inventors of the present invention have made intensive studies to achieve the above object, and found that two or more types of crystal phases with a layered rocksalt structure are contained, and one of the crystal phases with a layered rocksalt structure is contained in the transition metal layer. It has been found that a nickel-containing lithium-manganese composite oxide having a transition metal occupancy (g _3b ) at lattice positions of 77% or less can solve the above problems. The inventors of the present invention conducted further studies based on such knowledge, and completed the present invention.

That is, the present invention includes the following nickel-containing lithium-manganese composite oxide and its production method.
Section 1. General formula (1):
Li1 _+x (NiyMn1 _{-y ) 1-xO2 (} 1)
[In the formula, x and y represent −0.1<x<0.1 and 0.4≦y≦0.6, respectively. ]
is represented by
Containing two or more kinds of crystal phases with a layered rock salt structure,
Among them, the crystal phase (2) having a layered rock salt structure is a nickel-containing lithium-manganese composite oxide in which the transition metal occupancy (g _3b ) of lattice positions in the transition metal layer is 65.0 to 77.0%.
Section 2. Item 2. The nickel-containing lithium-manganese composite oxide according to item 1, wherein the crystal phase (2) having a layered rock salt structure has a transition metal occupancy (g _total ) per composition formula of 67.0 to 90.0%.
Item 3. Item 3. The nickel-containing lithium-manganese composite oxide according to Item 1 or 2, wherein the crystal phase (2) having a layered rock salt structure has a lattice constant a-axis value of 2.850 to 2.885 Å.
Section 4. 4. The nickel-containing lithium-manganese composite oxide according to any one of items 1 to 3, wherein the half width of the peak of the 104 plane in the X-ray diffraction pattern is 0.21 to 2.00°.
Item 5. Any one of items 1 to 4, wherein the existence ratio of the crystal phase (2) of the layered rock salt type structure is 10 to 40 mol% when the total amount of the crystal structure of the nickel-containing lithium manganese composite oxide is 100 mol%. 2. The nickel-containing lithium-manganese composite oxide according to item 1.
Item 6. A positive electrode active material for a lithium ion secondary battery, comprising the nickel-containing lithium manganese composite oxide according to any one of items 1 to 5.
Item 7. Item 7. A lithium ion secondary battery comprising the positive electrode active material for lithium ion secondary batteries according to Item 6.
Item 8. A method for producing a nickel-containing lithium-manganese composite oxide according to any one of Items 1 to 5,
(1) forming a precipitate under alkaline conditions from a mixed aqueous solution containing a manganese compound and a nickel compound;
(2) a step of subjecting the precipitate to a wet oxidation treatment; and (3) a step of heat-treating at 500 to 980°C in an oxidizing atmosphere in the presence of a lithium salt.

According to the present invention, a composite oxide that is useful as a positive electrode active material with excellent capacity and cycle characteristics without using cobalt, which is expensive and unevenly distributed as a resource, and without using an excessive amount of lithium. can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is drawing which shows typically the crystal phase of a hexagonal layered rock-salt type structure. 1 shows the XRD pattern fit results of the powder for evaluation obtained in Example 1. FIG. In the XRD pattern, the solid line indicates the calculated curve and + indicates the measured points. The bar under the XRD pattern indicates the calculated position of each crystal phase, and the line below it indicates the difference between the measured and calculated values. 1 shows charge-discharge characteristics after electrochemical activation of a lithium secondary battery using the powder for evaluation obtained in Example 1 as a positive electrode active material. c indicates charge, d indicates discharge, and the number indicates the number of cycles. FIG. 2 shows XRD pattern fitting results of the powder for evaluation obtained in Example 2. FIG. In the XRD pattern, the solid line indicates the calculated curve and + indicates the measured points. The bar under the XRD pattern indicates the calculated position of each crystal phase, and the line below it indicates the difference between the measured and calculated values. 1 shows charge-discharge characteristics after electrochemical activation of a lithium secondary battery using the powder for evaluation obtained in Example 2 as a positive electrode active material. c indicates charge, d indicates discharge, and the number indicates the number of cycles. 2 shows the result of fitting the XRD pattern of the powder for evaluation obtained in Comparative Example 1. FIG. In the XRD pattern, the solid line indicates the calculated curve and + indicates the measured points. The bar under the XRD pattern indicates the calculated position of each crystal phase, and the line below it indicates the difference between the measured and calculated values. 1 shows charge-discharge characteristics after electrochemical activation of a lithium secondary battery using the powder for evaluation obtained in Comparative Example 1 as a positive electrode active material. c indicates charge, d indicates discharge, and the number indicates the number of cycles.

As used herein, "contain" is a concept that includes both "comprise," "consist essentially of," and "consist of." Further, in this specification, when a numerical range is represented by A to B, it means A or more and B or less.

1. Nickel-Containing Lithium-Manganese Composite Oxide The nickel-containing lithium-manganese composite oxide of the present invention has the general formula (1):
Li1 _+x (NiyMn1 _{-y ) 1-xO2 (} 1)
[In the formula, x and y represent −0.1<x<0.1 and 0.4≦y≦0.6, respectively. ]
is represented by
Containing two or more kinds of crystal phases with a layered rock salt structure,
Among them, one crystal phase having a layered rock salt structure has a transition metal occupancy (g _3b ) at lattice positions in the transition metal layer of 77% or less.

In the above general formula (1), x is -0.1<x<0.1, more preferably -0.08<x<0.08. If X is -0.1 or less, the charge/discharge capacity is lowered, and if it is 0.1 or more, the impurity phase such as lithium carbonate increases, resulting in a decrease in the charge/discharge capacity.

In the above general formula (1), y is 0.4≤y≤0.6, preferably 0.45≤y≤0.55. If y is less than 0.4, a large amount of lithium is required to maintain the stoichiometric ratio, increasing costs and lowering voltage. On the other hand, when y exceeds 0.6, the structural stability during charging is lowered and the capacity is lowered.

In addition, the nickel-containing lithium-manganese composite oxide of the present invention contains two or more layered rock salt crystal phases. The layered rocksalt crystal structure that constitutes the layered rocksalt crystal phase is a crystal that often appears in inorganic compounds of the ABO ₂ type (A indicates an alkali metal and B indicates a transition metal) possessed by lithium cobaltate and lithium nickelate. Structure. It has a crystal structure in which a transition metal layer and a lithium layer are alternately laminated via oxide ions, and it is said that lithium ion desorption/insertion reactions are easy during charging and discharging.

Space group:

It preferably contains at least two kinds of crystal phases having a hexagonal layered rock salt structure attributed to . The nickel-containing lithium-manganese composite oxide of the present invention preferably contains two or more of the above crystal phases of the hexagonal layered rocksalt structure, and other crystal phases of the rocksalt structure (for example, a cubic rocksalt structure, etc.). It may be a mixed phase containing. In the case of a mixed phase, the total proportion of the crystalline phase of the hexagonal layered rock salt structure is preferably 50 to 90% by mass based on the entire mixed phase. In addition, the nickel-containing lithium-manganese composite oxide of the present invention may employ a configuration consisting only of two or more kinds of crystalline phases of a hexagonal layered rocksalt structure.

FIG. 1 is a diagram schematically showing a crystal phase of a hexagonal layered rock salt structure. In this structure, a lithium layer present at the 3a position and a transition metal layer present at the 3b position are alternately laminated via an oxide ion phase present at the 6c position. Lithium cobalt oxide provides a structure relatively close to such an ideal structure, but in the nickel-containing lithium-manganese composite oxide of the present invention, two or more crystal phases having different transition metal occupation ratios in the transition metal layer are present. coexist.

Crystal phases with different transition metal occupancy rates in the transition metal layer include (1) a crystal phase in which the 3b-position transition metal occupancy rate in the transition metal layer is 90.0% or more as the main phase, and (2) a subphase Examples thereof include a crystal phase in which the transition metal occupancy at the lattice position (3b position) in the transition metal layer (3b position transition metal occupancy in the transition metal layer; g _3b ) is 77.0% or less.

Of these, the crystal phase of the layered rocksalt structure existing as a subphase (hereinafter sometimes referred to as the “crystal phase of the layered rocksalt structure (2)”) is the 3b-position transition metal in the transition metal layer. It is essential that the occupancy (g _3b ) is between 65.0 and 77.0%. The crystal phase (2) of this layered rocksalt structure is a crystal phase with a lower occupancy of the 3b-position transition metal in the transition metal layer than the crystal phase of the usually obtained layered rocksalt crystal structure. However, due to the presence of this subphase, high capacity and excellent cycle characteristics can be obtained.

In the crystal phase (2) of this layered rock salt structure, the occupancy of the 3b-position transition metal in the transition metal layer is 65.0 to 77.0%, preferably 70.0 to 76.0%. In the crystal phase (2) with a layered rock salt structure, when the occupancy of the 3b-position transition metal in the transition metal layer is less than 65.0%, the Li ₂ MnO ₃ component with poor charge-discharge characteristics contained in the crystal phase (2) increases. too much, the charge/discharge characteristics deteriorate. In the crystal phase (2) of the layered rocksalt structure, when the occupancy of the 3b-position transition metal in the transition metal layer exceeds 77.0%, the capacity and cycle characteristics are degraded.

In addition, since the crystal phase (2) with the layered rock salt structure has a small occupancy of the 3b-position transition metal in the transition metal layer, The transition metal occupancy (g _total ) is also reduced as a result. Therefore, from the viewpoint of capacity and cycle characteristics, the crystalline phase (2) with a layered rock salt structure preferably has a transition metal occupancy (g _total ) per composition formula of 67.0 to 90.0%, and 75.0 to 88.0%. more preferred.

In addition, since the crystal phase (2) having a layered rock salt structure has a small occupancy of the 3b-position transition metal in the transition metal layer, the transition metal layer has many vacancies and tends to have a small lattice constant. Therefore, the crystal phase (2) having a layered rock salt structure preferably has a lattice constant a-axis value of 2.850 to 2.885 Å, more preferably 2.870 to 2.883 Å, from the viewpoint of capacity, cycle characteristics, and the like. Similarly, the lattice volume V is preferably 101.00-103.00 Å ³ , more preferably 101.50-102.95 Å ³ . The lattice constant a and the lattice volume V in the present specification mean values calculated assuming a hexagonal layered rock salt lattice.

Next, with regard to the crystal phase of the layered rocksalt structure existing as the main phase (hereinafter sometimes referred to as “the crystal phase of the layered rocksalt structure (1)”), the 3b-position transition metal in the transition metal layer It is preferable that the occupation rate is 90.0% or more. The crystal phase (1) of this layered rock salt type structure is the same as or similar to the crystal phase of the usually obtained layered rock salt type crystal structure. The occupancy of the 3b-position transition metal in the transition metal layer in the crystal phase (1) of this layered rock salt structure is preferably 90.0 to 100%, more preferably 90.2 to 95.0%.

In the layered rocksalt structure crystal phase (1), the 3b position transition metal occupancy in the transition metal layer is larger than that of the layered rocksalt structure crystal phase (2). The transition metal occupancy per formula (g _total ), which corresponds to the sum of the positions, also increases as a result. For this reason, the crystal phase (1) having a layered rock salt structure preferably has a transition metal occupancy (g _total ) per composition formula of 99.5 to 110.0%, more preferably 100.0 to 105.0%.

In addition, since the crystalline phase (1) with a layered rocksalt structure has a larger occupancy of the 3b position transition metal in the transition metal layer than the crystal phase (2) with a layered rocksalt structure, there are fewer vacancies in the transition metal layer. Lattice constant tends to be large. Accordingly, the crystal phase (1) having a layered rock salt structure preferably has a lattice constant a-axis value of 2.886 to 2.900 Å, more preferably 2.888 to 2.895 Å. Similarly, the lattice volume V is preferably 103.10-105.00 Å ³ , more preferably 103.20-104.00 Å ³ . The lattice constant a and the lattice volume V in the present specification mean values calculated assuming a hexagonal layered rock salt lattice.

Regarding the abundance of the layered rock salt crystal phase (1) and the layered rock salt crystal phase (2), the layered rock salt crystal phase (1) is the main phase and the layered rock salt crystal phase is Where (2) is a secondary phase, from the viewpoint of capacity, cycle characteristics, etc., the total amount of crystal structures possessed by the nickel-containing lithium manganese composite oxide of the present invention is 100 mol%, and the crystal phase (2) of the layered rock salt type structure ) is preferably 10 to 40 mol %, more preferably 15 to 35 mol %. Similarly, the existence ratio of the crystal phase (1) having a layered rock salt structure is preferably 60 to 90 mol %, more preferably 65 to 85 mol %.

The nickel-containing lithium-manganese composite oxide of the present invention includes cubic rocksalt-type oxides (such as NiO), lithium salts such as lithium carbonate and lithium hydroxide, and other may contain an impurity phase such as nickel or manganese compounds (including their hydrates and composite compounds), and the amount thereof is 10 mol %, where the total amount of the nickel-manganese composite oxide of the present invention is 100 mol % 5 mol % or less is particularly preferable.

In addition, in the nickel-containing lithium manganese composite oxide of the present invention, the peak of the 104 plane near 2θ = 45 ° in the X-ray diffraction pattern can be slightly lower in crystallinity from the viewpoint of capacity, cycle characteristics, etc. The half width is preferably 0.21 to 2.00°, more preferably 0.22 to 1.00°.

From the above characteristics, the nickel-containing lithium-manganese composite oxide of the present invention exhibits capacity and cycle characteristics superior to those of the conventional material composed only of the main phase, the crystalline phase (1) of layered rocksalt structure.

2. Positive Electrode Active Material for Lithium Ion Secondary Battery and Lithium Ion Secondary Battery The nickel-containing lithium-manganese composite oxide of the present invention described above can be used as a positive electrode active material for a lithium ion secondary battery. A positive electrode mixture prepared by mixing such a positive electrode active material of the present invention with a known conductive agent and a binder is supported on a positive electrode current collector such as aluminum, nickel, stainless steel, carbon cloth, etc. to form a positive electrode. can be manufactured. Examples of conductive agents that can be used include carbon materials such as graphite, cokes, carbon black, and acicular carbon. The negative electrode active material is also not particularly limited, and examples thereof include metallic lithium, graphite, Si—SiO negative electrodes, LTO (Li ₄ Ti ₅ O ₁₂ ) negative electrodes, and the like. These negative electrode active materials can also be supported on a negative electrode current collector made of aluminum, copper, nickel, stainless steel, carbon, or the like using a conductive agent, a binder, or the like, as necessary, to produce a negative electrode. . The electrolyte is not particularly limited, and organic electrolytes such as LiPF ₆ as an electrolyte salt dissolved in various solvents such as ethyl carbonate (EC) and dimethyl carbonate (DMC), Li ₂ SP ₂ S ₅ , Li ₂ S -GeS ₂ -P ₂ S ₅ , Li ₂ S-SiS ₂ -Li ₂ PO ₄ and other inorganic sulfide-based solid electrolytes, and high polymers having lithium ion conductivity. The separator is not particularly limited, and examples thereof include polyethylene and polypropylene.

3. Method for Producing Nickel-Containing Lithium-Manganese Composite Oxide The present invention further includes the aforementioned method for producing the nickel-containing lithium-manganese composite oxide of the present invention. The method for producing a nickel-containing lithium-manganese composite oxide of the present invention comprises:
(1) forming a precipitate under alkaline conditions from a mixed aqueous solution containing a manganese compound and a nickel compound;
(2) a step of subjecting the precipitate to a wet oxidation treatment; and (3) a step of heat-treating at 500 to 980° C. in an oxidizing atmosphere in the presence of a lithium salt.

(3-1) Process (1)
The manganese compound to be used is not particularly limited, and manganese (II) chloride, manganese sulfate (II), manganese acetate (II), manganese acetate (III), manganese nitrate (II), manganese acetylacetate (II), acetyl A wide range of known agents can be used, including hydrates such as manganese acetate (III) and potassium permanganate (VII). Manganese oxide and metallic manganese can also be used as water-soluble salts by dissolving them in an appropriate acid.

The nickel compound to be used is not particularly limited, and a wide range of known compounds including hydrates such as nickel (II) nitrate, nickel (II) acetate, nickel (II) chloride, and nickel (II) sulfate can be used. can. Nickel oxide and metallic nickel can also be used as water-soluble salts by dissolving them in an appropriate acid.

The blending ratio of the nickel compound and the manganese compound to be used can be the same as the blending ratio of the intended nickel-containing lithium-manganese composite oxide of the present invention.

The metal salt concentration in the mixed aqueous solution containing the manganese compound and the nickel compound is not particularly limited, and can be appropriately determined so that a uniform mixed aqueous solution can be formed and a coprecipitate can be smoothly formed. Generally, the total concentration of the nickel compound and manganese compound is preferably 0.01-5 mol/l, more preferably 0.1-2 mol/l.

As a solvent for the mixed aqueous solution containing a manganese compound and a nickel compound, water alone or a water-alcohol mixed solvent containing a water-soluble alcohol such as methanol or ethanol can be used. A water-soluble alcohol can also be used as a precipitating agent when using potassium permanganate as a manganese source. In addition, water-soluble alcohol can be used as an antifreeze solution when dripping at a low temperature of 0°C or less, making it possible to form a precipitate at a temperature below 0°C. When using a water-soluble alcohol, the amount used can be appropriately set depending on the desired precipitation temperature, etc., but usually the water-soluble alcohol is 50 parts by weight or less (especially 5 to 45 parts by weight) per 100 parts by weight of water. ).

A method for forming a precipitate (coprecipitate) from a mixed aqueous solution containing a manganese compound and a nickel compound includes making the mixed aqueous solution alkaline. Conditions for forming a good-quality precipitate cannot be generalized because they differ depending on the kind and concentration of each compound contained in the mixed aqueous solution, but usually pH 8 or higher is preferable, and pH 11 to 14 is more preferable.

The method for making the mixed aqueous solution containing the manganese compound and the nickel compound alkaline is not particularly limited, and the mixed aqueous solution containing the manganese compound and the nickel compound can be mixed with the alkaline solution. As a mixing method at this time, it is possible to employ a wide range of known mixing methods, and there is no particular limitation. For example, the mixed aqueous solution can be gradually added to the alkaline solution. Examples of the alkali source that forms the alkali solution include sodium hydroxide, potassium hydroxide, ammonia, lithium hydroxide (including hydrates thereof), and the like. Regarding the alkali concentration, for example, 0.1 to 20 mol/l is preferable, and 0.3 to 10 mol/l is more preferable. A water-alcohol mixed solvent can also be obtained by adding the above-mentioned water-soluble alcohol to the alkaline solution.

When forming the precipitate, it is preferable to use a known vessel such as a constant temperature bath capable of adjusting and maintaining the temperature to control the temperature in order to mitigate deterioration of the material due to the heat of neutralization. Empirically, there is a tendency that the lower the temperature at which the precipitate is formed, the easier it is to form a precipitate with a uniform transition metal distribution. Therefore, the temperature of the alkaline solution is preferably -50°C to +30°C, more preferably -20°C to +20°C. Here, when the set temperature is set to 0° C. or lower, it is preferable to add the above water-soluble alcohol as an antifreeze to the alkaline solution.

During the precipitation reaction, it is preferable to add the mixed aqueous solution containing the manganese compound and the nickel compound to the alkaline solution while gradually dropping them, from the viewpoint of suppressing the side reaction associated with the generation of heat of neutralization. The dropping time is not particularly limited, but is usually preferably 1 to 10 hours, more preferably 2 to 5 hours.

(3-2) Process (2)
In step (2), the precipitate obtained in step (1) is subjected to wet oxidation treatment. In the step (2), an oxidizing gas such as air or oxygen is blown (bubbled) into an alkaline solution containing the precipitate to oxidatively ripen the precipitate to produce a precursor highly reactive with lithium. The blown gas is not limited as long as it contains oxygen. Air may be used, but oxygen is preferred from the viewpoint of shortening the oxidation time. In the case of oxygen, an industrial oxygen generator can be used as well as a commonly used cylinder. The temperature of the wet oxidation is not particularly limited, and can be, for example, 0 to 150°C, particularly 10 to 100°C. From the viewpoint of allowing the reaction to proceed sufficiently, the wet oxidation time is preferably longer, but is preferably 1 hour or longer, more preferably 24 hours or longer, and even more preferably 48 hours or longer.

(3-3) Process (3)
In step (3), the aged product obtained in step (2) is heat-treated in the presence of a lithium salt. Here, from the viewpoint of reducing impurities derived from the above water-soluble salts, the aged product obtained in the above step (2) is washed with distilled water or the like to remove salts before the heat treatment in the presence of lithium salt. After that, it is preferable to filter. In addition, when heat treatment is performed in the presence of lithium salt, lithium salt is added to the aged product from which salts have been removed as described above, and the raw material for heat treatment is heated at 500 to 980 ° C in an oxidizing atmosphere in the presence of lithium salt. It is preferable to heat-treat at Of course, it is also possible to add a lithium salt to the reactant (aged product) obtained in the above step (2) as it is and heat-treat it at 500 to 980°C in an oxidizing atmosphere in the presence of a lithium salt as a raw material for heat treatment.

As a specific method for coexisting the aged product and the lithium salt during the heat treatment, a known method can be used, and there is no particular limitation. A method of mixing with a lithium salt can be mentioned.

Moreover, as a raw material for heat treatment, a dried aged product may be used. When using a dried aged product, the aged product and the lithium salt are separated before drying from the viewpoint that it is easy to avoid solidification due to residual alkali during drying and difficulty in uniform mixing with the lithium salt. Mixing is preferred.

As the lithium salt, a wide range of known lithium salts can be used, and there is no particular limitation. Specifically, lithium acetate, lithium nitrate, lithium chloride, hydrates thereof, and the like can be used in addition to inexpensive lithium carbonate and lithium hydroxide which is highly reactive with the aged product. Lithium perchlorate and its hydrate can also be used as an oxidizing agent in addition to the above lithium salt. These lithium salts can be used alone or in combination of two or more.

As the amount of the lithium salt added to the aged product, it is preferable to adjust the molar amount of lithium to the number of moles of nickel and manganese in the aged product (Li/(Ni+Mn) ratio) according to the composition of the target product. . In other words, since the x value in the general formula (1) is -0.1<x<0.1, the molar amount of lithium (Li/(Ni+Mn) ratio) with respect to the molar amount of nickel and manganese in the aged product is 0.82 ~ 1.22 is preferred, and 0.86-1.17 is more preferred. When the amount of Li is excessive, the nickel-containing lithium-manganese composite oxide is likely to have uniform and single crystals, and the nickel-containing lithium-manganese of the present invention contains two or more kinds of layered rocksalt-type crystal phases. Composite oxides are difficult to obtain.

Here, if the lithium salt is insoluble in water, after dry mixing, it should be pulverized well with a vibration mill or the like. If it is water-soluble, after sufficiently dispersing the precipitate in an aqueous solution containing the lithium salt, put it in a mixer to make a uniform slurry. Fabrication is preferred. The slurry or the like can be dried with a dryer and re-pulverized if necessary. As a result, it is possible to make the mixture of the aged product and the lithium salt uniform in color tone, and to improve the reactivity by not including coarse particles. In addition, the method of mixing before pulverization can be dry and mixed as it is, but it is also possible to obtain a mixture by adding an aged product to an aqueous solution of lithium salt once and drying it. , from 0.1 to 10 mol/l. The drying temperature is preferably 100° C. or lower, more preferably 60° C. or lower, from the viewpoint of increasing the viscosity of the slurry and mixing the aged product and the lithium salt more uniformly. Vacuum, freeze-drying, or the like can also be used for drying.

The heat treatment method is not particularly limited as long as it is a treatment that applies heat, and a wide range of known methods can be employed. Among them, it is preferable to perform the calcination treatment from the viewpoint that the heat treatment can be easily performed. The heat treatment is performed in an oxidizing atmosphere. In this specification, heat treatment in an oxidizing atmosphere means heat treatment in an oxygen-containing atmosphere such as air or an oxygen stream. By performing the heat treatment in an oxidizing atmosphere, the lattice parameters (lattice constant, lattice volume, etc.) in the nickel-containing lithium manganese composite oxide of the present invention, the transition metal occupancy (g _3b ) at the lattice position in the transition metal layer, The transition metal occupancy rate (g _total ) and the like per composition formula can be set within the numerical range described above, and thus the nickel-containing lithium-manganese composite oxide of the present invention can be obtained.

The heat treatment temperature is 500-980°C, preferably 600-950°C, more preferably 750-900°C. If the heat treatment temperature is less than 500° C., the resulting nickel-containing lithium-manganese composite oxide becomes excessively reactive with the electrolytic solution, resulting in poor cycle characteristics. When the heat treatment temperature exceeds 980°C, uniform and single crystals are obtained in the nickel-containing lithium-manganese composite oxide. No product is obtained, and the capacity and cycle characteristics deteriorate. In this specification, the heat treatment temperature means the maximum temperature reached during the heat treatment.

The heat treatment time is preferably 30 minutes or longer, more preferably 1 hour or longer, while maintaining the temperature within the above heat treatment temperature range from the viewpoint of sufficient reaction. Although the upper limit of the heat treatment time is not particularly limited, it is preferably 100 hours or less, more preferably 50 hours or less, from the viewpoint of suppressing an increase in production cost.

After the heat treatment, step (3) can be repeated multiple times, for example, two or three times, as necessary, in order to obtain a nickel-containing lithium-manganese composite oxide with better charge/discharge properties. Moreover, the obtained heat-treated product can be pulverized as necessary.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to such examples, and can of course be embodied in various forms without departing from the gist of the present invention.

EXAMPLES Hereinafter, embodiments of the present invention will be described more specifically based on Examples, but the present invention is not limited to these.

Example 1
36.35 g of nickel (II) nitrate hexahydrate and 24.74 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol/batch, Ni:Mn molar ratio 1:1) were added to 500 ml of distilled water and completely dissolved. to prepare a metal salt solution. A sodium hydroxide aqueous solution was prepared by dissolving 50 g of sodium hydroxide in 500 ml of distilled water in another beaker (made of titanium). A Ni—Mn precipitate was formed by gradually dropping the metal salt solution into the temperature-controlled sodium hydroxide solution over a period of about 3 hours. After confirming that the reaction solution was completely alkaline (pH 11 or higher), the precipitate formation reaction was completed. The alkaline solution containing the prepared precipitate was taken out from the constant temperature bath, and oxygen was blown into the mixture at room temperature for 2 days while stirring to ripen the precipitate.

The aged precipitate was taken out from the beaker, washed with distilled water to remove excess alkali components, salts, etc., and filtered. After that, 0.125 mol (18.47 g) of lithium carbonate corresponding to a Li/(Ni+Mn) ratio of 1.00 was dispersed in 200 ml of distilled water, and then mixed with the filtered sediment in a mixer to prepare a slurry mixture. The mixture was pulverized and used as a raw material for firing. Put the firing raw material in a crucible, heat it up to 850°C in the atmosphere in an electric furnace for 1 hour, fire at that temperature for 5 hours, cool it down to around room temperature in the furnace, remove it from the furnace, crush it and evaluate it. powder for use.

Evaluation by X-ray diffraction (Example 1)
FIG. 2 shows the fitted state of the XRD pattern of the powder for evaluation obtained in Example 1, and Table 1 shows the crystallographic parameters obtained by fitting. From FIG. 2, it is clear that the XRD pattern of the powder for evaluation obtained in Example 1 can fit two hexagonal layered rock salt crystal phases having different lattice constants. From the crystallographic parameters listed in Table 1, the powder for evaluation obtained in Example 1 consisted of about 66 mol% of the main phase and 34 mol% of the subphase, and the subphase had a lower a-axis value than the main phase. (2.885 Å or less), low 3b position transition metal occupancy (g _3b value, 77.0% or less), low total transition metal content per composition formula (g _total = g _3a + g _3b value, 90.0% or less) It is clear that the nickel-containing lithium-manganese composite oxide of the present invention was obtained. Furthermore, the powder for evaluation obtained in Example 1 had a large half width of 0.46° for the 104 peak near 2θ = 45°, clearly indicating that the nickel-containing lithium-manganese composite oxide of the present invention was obtained. .

Evaluation by chemical analysis (Example 1)
The amount of Li in the powder for evaluation obtained in Example 1 was determined by ICP emission analysis, and the amount of Ni and Mn was determined by fluorescent X-ray analysis. Table 1 shows the results. It is clear from the Li/(Ni+Mn) molar ratio value and the Ni/(Ni+Mn) molar ratio value that the nickel-containing lithium-manganese composite oxide of the present invention was obtained.

Charge-discharge characteristic evaluation (Example 1)
20 mg of the powder for evaluation obtained in Example 1 was mixed with 5 mg of acetylene black and 0.5 mg of polytetrafluoroethylene powder to prepare a positive electrode mixture. This composite material was pressed against an aluminum mesh to prepare a positive electrode. A coin-type lithium secondary battery was fabricated using this positive electrode in a glove box, using an organic electrolyte of 1M by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate and dimethyl carbonate, and using metallic lithium foil as the negative electrode. . In order to optimize the charge/discharge characteristics of the nickel-containing lithium-manganese composite oxide of the present invention, an electrochemical activation method by a stepwise charge method was carried out. A specific activation method was as follows. The positive electrode was first charged to 80 mAh/g at a current density of 40 mA/g and then discharged to 2.0 V at the same current density. After that, charging/discharging was performed by increasing the charging capacity by 40 mAh/g, and discharging was performed in the same manner. After charging to the 4th cycle (200mAh/g), discharging to 2.0V, charging to 4.8V in the last 5th cycle, holding at that voltage to 10mA/g, and discharging to complete the activation. rice field. After the 6th cycle, the current density was the same, and 29 cycles of charging and discharging were performed in the potential range of 2.0-4.6 V to understand the cycle characteristics.

Table 1 and FIG. 3 show the evaluation results of charge-discharge characteristics using the evaluation powder obtained in Example 1. The powder for evaluation obtained in Example 1 has a higher initial charge/discharge capacity (Q _5c and Q _5d ) and a higher discharge power (E _5d ), high post-cycle discharge capacity (Q _34d ), and high cycle characteristics (100Q _34d /Q _5d ), demonstrating the superiority of the nickel-containing lithium-manganese composite oxide of the present invention in charge-discharge characteristics. In addition, in Table 1, Q _5c is the charge capacity at the 5th cycle and corresponds to the initial charge capacity. Q _5d is the discharge capacity at the 5th cycle and corresponds to the initial discharge capacity. V _5d is the fifth cycle discharge voltage and corresponds to the initial discharge voltage. E _5d indicates the discharge power of the 5th cycle. Q _34d is the discharge capacity at the 34th cycle, and 100Q _34d /Q _5d indicates the capacity retention rate (cycle characteristics) after 29 cycles of charging and discharging.

Example 2
A sample was prepared in the same manner as in Example 1, except that the final firing temperature was 950°C for 5 hours in the atmosphere.

Evaluation by X-ray diffraction (Example 2)
FIG. 4 shows the XRD pattern fit of the powder for evaluation obtained in Example 2, and Table 1 shows the crystallographic parameters obtained by fitting. From FIG. 4, it is clear that the XRD pattern of the powder for evaluation obtained in Example 2 can fit two hexagonal layered rock salt type crystal phases having different lattice constants. From the crystallographic parameters listed in Table 1, the powder for evaluation obtained in Example 2 consisted of 78 mol% of the main phase and 22 mol% of the subphase, and the subphase had a lower a-axis value than the main phase ( 2.885 Å or less), low occupancy of 3b position transition metals (g _3b value, 77.0% or less), low total transition metal content per composition formula (g _total = g _3a + g _3b value, 90.0% or less) It is clear that the nickel-containing lithium-manganese composite oxide of the present invention was obtained. Furthermore, the powder for evaluation obtained in Example 2 has a large half-value width of 0.24° for the 104 peak near 2θ=45°, clearly indicating that the nickel-containing lithium-manganese composite oxide of the present invention was obtained.

Evaluation by chemical analysis (Example 2)
The amount of Li in the powder for evaluation obtained in Example 2 was determined by ICP emission spectrometry, and the amounts of Ni and Mn were determined by fluorescent X-ray analysis. Table 1 shows the results. It is clear from the Li/(Ni+Mn) molar ratio value and the Ni/(Ni+Mn) molar ratio value that the nickel-containing lithium-manganese composite oxide of the present invention was obtained.

Charge-discharge characteristic evaluation (Example 2)
The powder for evaluation obtained in Example 2 was subjected to electrode mixture preparation, electrochemical activation, and cycle characteristic evaluation in the same manner as in Example 1. Table 1 and FIG. 5 show the evaluation results of charge-discharge characteristics of the powder for evaluation obtained in Example 2. The powder for evaluation obtained in Example 2 has a higher initial charge/discharge capacity (Q _5c and Q _5d ) and a higher discharge power (E _5d ), high post-cycle discharge capacity (Q _34d ), and high cycle characteristics (100Q _34d /Q _5d ), demonstrating the superiority of the nickel-containing lithium-manganese composite oxide of the present invention in charge-discharge characteristics.

Comparative example 1
A sample was prepared in the same manner as in Example 1, except that the final sintering temperature was 1000° C. for 5 hours in air.

Evaluation by X-ray diffraction (Comparative Example 1)
FIG. 6 shows the fitted state of the XRD pattern of the powder for evaluation obtained in Comparative Example 1, and Table 1 shows the crystallographic parameters obtained by fitting. From FIG. 6, it is clear that the XRD pattern of the powder for evaluation obtained in Comparative Example 1 can be fitted to only one type of hexagonal layered rock salt crystal phase. From the crystallographic parameters listed in Table 1, the evaluation powder obtained in Comparative Example 1 has only 100 mol% of the main phase, the a-axis value (2.885 Å or less), the 3b-position transition metal occupancy (g _3b value , 77.0% or less), the total amount of transition metals per composition formula (g _total = g _3a + g _3b value, 90.0% or less) are both outside the scope of the present invention n, and the nickel-containing lithium manganese composite oxide of the present invention is Clearly not. Furthermore, the powder for evaluation obtained in Comparative Example 1 has a small half width of 0.20° for the 104 peak near 2θ = 45°, and it is clear that the nickel-containing lithium manganese composite oxide of the present invention was not obtained. .

Evaluation by chemical analysis (Comparative Example 1)
The amount of Li in the powder for evaluation obtained in Comparative Example 1 was determined by ICP emission analysis, and the amount of Ni and Mn was determined by fluorescent X-ray analysis. Table 1 shows the results. From the values of Li/(Ni+Mn) molar ratio and Ni/(Ni+Mn) molar ratio, it was clarified that the difference from the nickel-containing lithium-manganese composite oxide of the present invention is slight.

Charge/discharge characteristics evaluation (Comparative example 1)
The powder for evaluation obtained in Comparative Example 1 was also subjected to electrode mixture preparation, electrochemical activation, and cycle characteristic evaluation in the same manner as in Example 1. Table 1 and FIG. 7 show the evaluation results of charge-discharge characteristics of the powder for evaluation obtained in Comparative Example 1. The powder for evaluation obtained in Comparative Example 1 has a lower initial charge-discharge capacity (Q _5c and Q _5d ) and a lower discharge power ( E _5d ), low cycle discharge capacity (Q _34d ), and low cycle characteristics (100Q _34d /Q _5d ), which is disadvantageous in charge and discharge characteristics because it is different from the nickel-containing lithium manganese composite oxide of the present invention. is clear.

From the results of the above examples and comparative examples, the nickel-containing lithium manganese composite oxide of the present invention, which is characterized by containing a unique hexagonal layered rock salt crystal phase as a subphase, has excellent charge and discharge characteristics. It is clear that it is a substance.

Claims (8)

General formula (1):
Li1 _+x (NiyMn1 _{-y ) 1-xO2 (} 1)
[In the formula, x and y represent −0.1<x<0.1 and 0.4≦y≦0.6, respectively. ]
is represented by
Containing two or more kinds of crystal phases with a layered rock salt structure,
Among them, the crystal phase (2) having a layered rock salt structure is a nickel-containing lithium-manganese composite oxide in which the transition metal occupancy (g _3b ) of lattice positions in the transition metal layer is 65.0 to 77.0%. 2. The nickel-containing lithium-manganese composite oxide according to claim 1, wherein the crystal phase (2) having a layered rock salt structure has a transition metal occupation ratio (g _total ) per composition formula of 67.0 to 90.0%. 3. The nickel-containing lithium-manganese composite oxide according to claim 1, wherein the crystal phase (2) having a layered rock salt structure has a lattice constant a-axis value of 2.850 to 2.885 Å. The nickel-containing lithium-manganese composite oxide according to any one of claims 1 to 3, wherein the half width of the peak of the 104 plane in the X-ray diffraction pattern is 0.21 to 2.00° or more. 5. Any one of claims 1 to 4, wherein the existence ratio of the crystal phase (2) of the layered rock salt type structure is 10 to 40 mol% when the total amount of the crystal structure possessed by the nickel-containing lithium manganese composite oxide is 100 mol%. 2. The nickel-containing lithium-manganese composite oxide according to claim 1. A positive electrode active material for a lithium ion secondary battery, comprising the nickel-containing lithium manganese composite oxide according to any one of claims 1 to 5. A lithium ion secondary battery comprising the positive electrode active material for lithium ion secondary batteries according to claim 6 . A method for producing a nickel-containing lithium-manganese composite oxide according to any one of claims 1 to 5,
(1) forming a precipitate under alkaline conditions from a mixed aqueous solution containing a manganese compound and a nickel compound;
(2) a step of subjecting the precipitate to a wet oxidation treatment; and (3) a step of heat-treating at 500 to 980°C in an oxidizing atmosphere in the presence of a lithium salt.

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