JP2022116212A - Nickel manganese cobalt composite hydroxide and lithium nickel manganese cobalt composite oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material which allows especially a sodium content to be surely decreased, and which enables further enhancement in battery characteristic by achievement of a high porosity and long life, and its precursor.

SOLUTION: Nickel manganese cobalt composite hydroxide is a precursor of a cathode active material, comprising secondary particles resulting from agglomeration of primary particles containing nickel, manganese and cobalt, or the primary and secondary particles. In the nickel manganese cobalt composite hydroxide, the sodium content is less than 0.0005 mass%. The nickel manganese cobalt composite hydroxide particles have a porosity of over 20% to 50%.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention provides a nickel-manganese-cobalt composite hydroxide, which is a precursor of a positive electrode active material, composed of secondary particles in which primary particles containing nickel, manganese, and cobalt are aggregated, or primary particles and secondary particles, and lithium It relates to a nickel-manganese-cobalt composite oxide.

In recent years, with the spread of mobile electronic devices such as smartphones, tablet terminals, and notebook computers, high energy density, compact and lightweight non-aqueous electrolyte secondary batteries, as well as batteries for hybrid and electric vehicles, are becoming popular. The development needs for output secondary batteries are expanding.

As a secondary battery that can meet such needs, there is a lithium ion secondary battery. A lithium-ion secondary battery is composed of a positive electrode, a negative electrode, an electrolytic solution, and the like, and a material capable of desorbing and intercalating lithium is used as an active material for the positive electrode and the negative electrode. Lithium ion secondary batteries are still being actively researched and developed. Since a high-class voltage can be obtained, it is being put to practical use as a battery with high energy density.

Among these, lithium-nickel-manganese-cobalt composite oxides are attracting attention as a material that has good cycle characteristics of battery capacity, low resistance and high output. It is also suitable as a vehicle power source, and is regarded as important as a vehicle power source. Lithium-nickel-manganese-cobalt composite oxides are generally produced by mixing a precursor nickel-manganese-cobalt composite hydroxide with a lithium compound and calcining the mixture.

This nickel-manganese-cobalt composite hydroxide contains impurities such as sulfate radicals, chlorine radicals and sodium derived from raw materials and chemicals used in the manufacturing process. These impurities induce side reactions and worsen the reaction with lithium in the process of mixing and firing the nickel-manganese-cobalt composite hydroxide and the lithium compound. It lowers the crystallinity of the composite oxide.

Lithium-nickel-manganese-cobalt composite oxide with reduced crystallinity due to the influence of impurities inhibits the diffusion of lithium in the solid phase when forming a battery as a positive electrode active material, resulting in a decrease in battery capacity. In addition, since these impurities hardly contribute to the charge/discharge reaction, in the configuration of the battery, the negative electrode material must be used in excess for the irreversible capacity of the positive electrode material. As a result, the capacity per weight or per volume of the battery as a whole becomes small, and excess lithium accumulates in the negative electrode as irreversible capacity, which poses a safety problem.

Impurities include sulfate radicals, chlorine radicals, sodium, and the like, and techniques for removing these impurities have been disclosed.

For example, in Patent Document 1, a crystallization step is performed to obtain a niobium-containing transition metal composite hydroxide, and the obtained niobium-containing transition metal composite hydroxide is treated with an aqueous solution of a carbonate such as potassium carbonate, sodium carbonate, or ammonium carbonate. It is disclosed that sulfate radicals and chlorine radicals are reduced by washing with.

Further, in Patent Document 2, in the step of producing a nickel-manganese-cobalt composite hydroxide from a crystallization reaction, the alkaline solution used for pH adjustment is a mixed solution of an alkali metal hydroxide and a carbonate, thereby removing impurities It is disclosed that the sulfate group, chlorine group, and carbonate group are reduced.

Further, in Patent Documents 3 and 4, nickel-manganese composite hydroxide particles or nickel composite hydroxide particles having a void structure inside the particles obtained in the crystallization step are treated with potassium carbonate, sodium carbonate, potassium hydrogencarbonate and It is disclosed that sulfate radicals, chlorine radicals and sodium are reduced by washing with an aqueous carbonate solution such as sodium bicarbonate.

Further, in Patent Document 5, a nickel-cobalt-M element-containing aqueous solution or aqueous dispersion obtained by mixing a nickel ammine complex, a cobalt ammine complex, and an M element source is heated to form a nickel ammine complex and a cobalt ammine complex. It is disclosed to use a nickel-cobalt-M element-containing composite compound that is thermally decomposed and contains less impurities such as sulfate radicals, chlorine radicals, sodium and iron.

JP 2015-122269 A JP 2016-117625 A WO2015/146598 JP 2015-191848 A WO2012/020768

However, Patent Documents 1 and 2 do not mention removal of sodium at all. In addition, regarding Patent Documents 3 and 4, even in solid-level precursors with a low porosity of 2 to 4%, sodium still remains at 0.017 or 0.001% by mass, and sodium reduction is unsatisfactory. It is enough. Furthermore, regarding Patent Document 5, since a nickel-cobalt-M element-containing composite compound is obtained by thermal decomposition, from the viewpoint of the spherical shape, particle size distribution, and specific surface area of the particles, sufficient battery characteristics are obtained when used as a positive electrode active material. It is questionable whether In addition to the removal of impurities, it is expected to further improve the battery characteristics by increasing the porosity.

Therefore, the object of the present invention is to develop a lithium-ion secondary battery in which the content of sodium, among impurities that hardly contribute to the charge-discharge reaction, can be reliably reduced, and the porosity can be increased to further improve the battery characteristics. An object of the present invention is to provide a nickel-manganese-cobalt composite hydroxide and a lithium-nickel-manganese-cobalt composite oxide, which are precursors of positive electrode active materials.

A nickel-manganese-cobalt composite hydroxide according to one aspect of the present invention is a positive electrode active material composed of secondary particles in which primary particles containing nickel, manganese, and cobalt are aggregated, or the primary particles and the secondary particles. A nickel-manganese-cobalt composite hydroxide as a precursor, wherein the sodium content in the nickel-manganese-cobalt composite hydroxide is less than 0.0005% by mass, and particles of the nickel-manganese-cobalt composite hydroxide is characterized by having a porosity of 20 to 50%.

In this way, nickel-manganese-cobalt composite water, which is a precursor of the positive electrode active material of a lithium-ion secondary battery capable of reliably reducing the sodium content and further improving the battery characteristics by increasing the porosity. Oxide can be provided.

At this time, in one aspect of the present invention, the nickel-manganese-cobalt composite hydroxide may have a specific surface area of 30 to 40 m ² /g.

In this way, by increasing the specific surface area, the nickel-manganese-cobalt composite hydroxide, which is a precursor of the positive electrode active material capable of obtaining a lithium-ion secondary battery capable of further improving battery characteristics, is used. can provide.

At this time, in one aspect of the present invention, the content of sulfate radicals contained in the nickel-manganese-cobalt composite hydroxide may be 0.2% by mass or less, and the content of chlorine radicals may be 0.01% by mass or less.

In this way, the nickel-manganese-cobalt composite water, which is a precursor of the positive electrode active material of the lithium-ion secondary battery, can reliably reduce the contents of sulfate radicals, chlorine radicals and sodium and further improve battery characteristics. Oxide can be provided.

At this time, in one aspect of the present invention, [(d90−d10)/average particle size], which is an index showing the spread of the particle size distribution of the nickel-manganese-cobalt composite hydroxide, may be 0.55 or less.

In this way, the proportion of fine particles and large-sized particles in the positive electrode active material is reduced, so that a lithium ion secondary battery using this positive electrode active material for the positive electrode has excellent safety and good cycle characteristics. and battery output can be obtained.

At this time, in one aspect of the present invention, the nickel-manganese-cobalt composite hydroxide has the general formula: Ni _{x Mny} Co _z M _t (OH) _2+a (where x+y+z+t=1, 0.20≦x≦0.20≦x≦0.20). 80, 0.10 ≤ y ≤ 0.90, 0.10 ≤ z ≤ 0.50, 0 ≤ t ≤ 0.10, 0 ≤ a ≤ 0.5, M is Mg, Ca, Al, Ti, V , Cr, Zr, Nb, Mo, and W).

In this way, it is a precursor of a positive electrode active material for a lithium ion secondary battery that can reliably reduce the content of the nickel manganese cobalt composite hydroxide and further improve the battery characteristics by increasing the porosity. A certain nickel-manganese-cobalt composite hydroxide can be provided.

In one aspect of the present invention, a secondary particle in which primary particles containing lithium, nickel, manganese, and cobalt are aggregated, or a lithium-nickel-manganese-cobalt composite oxide composed of the primary particles and the secondary particles, The sodium content contained in the lithium-nickel-manganese-cobalt composite oxide is determined under the following measurement conditions and is less than 0.0005% by mass, and the lithium-nickel-manganese-cobalt composite oxide has a porosity of 20 to 50%. It is characterized by
[Record]
<Conditions for measuring sodium content>
1 g of an analysis sample is acidolyzed to prepare 100 mL of a measurement sample liquid, and the measurement is performed with an atomic absorption spectrometer.

In this way, it is possible to reliably reduce the sodium content and provide a lithium-nickel-manganese-cobalt composite oxide that is a positive electrode active material for a lithium-ion secondary battery capable of increasing the capacity.

At this time, in one aspect of the present invention, the lithium-nickel-manganese-cobalt composite oxide has a sulfate group content of 0.15% by mass or less, a chlorine group content of 0.005% by mass or less, and a Me site occupancy rate of may be 93.0% or more.

In this way, a lithium nickel manganese cobalt composite oxide is provided which is a positive electrode active material for a lithium ion secondary battery capable of reliably reducing the contents of sulfate radicals, chlorine radicals and sodium and increasing the capacity. be able to.

According to the present invention, a nickel-manganese-cobalt composite, which is a precursor of a positive electrode active material for a lithium-ion secondary battery capable of reliably reducing the sodium content and further improving the battery characteristics by increasing the porosity, in particular. Hydroxides and lithium-nickel-manganese-cobalt composite oxides can be provided.

FIG. 1 is a cross-sectional SEM photograph of a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention, showing that the internal structure is a hollow structure. FIG. 2 is a process drawing showing an outline of a method for producing a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention.

As a result of intensive studies to solve the above problems, the present inventors have found that in the production of nickel-manganese-cobalt composite hydroxide, the reaction atmosphere in the crystallization step is controlled, and the alkaline solution used in the crystallization step is replaced with alkali metal hydroxide. In the washing step, the transition metal composite hydroxide obtained in the crystallization step is washed with an ammonium hydrogen carbonate solution, which is a washing liquid containing hydrogen carbonate (bicarbonate). The present invention has been completed based on the knowledge that the impurities of sulfate group, chlorine group and sodium can be reduced more efficiently and to a lower concentration by washing with . Preferred embodiments of the present invention will be described below.

The embodiments described below do not unduly limit the scope of the invention described in the claims, and can be modified without departing from the gist of the invention. Moreover, not all the configurations described in the present embodiment are essential as the solution means of the present invention. A nickel-manganese-cobalt composite hydroxide, a method for producing a nickel-manganese-cobalt composite hydroxide, and a lithium-nickel-manganese-cobalt composite oxide according to one embodiment of the present invention will be described in the following order.
1. Nickel manganese cobalt composite hydroxide 2 . Lithium nickel manganese cobalt composite oxide 3 . Method for producing nickel-manganese-cobalt composite hydroxide 3-1. Crystallization step 3-1-1. Nucleation step 3-1-2. Particle growth step 3-2. cleaning process

<1. Nickel manganese cobalt composite hydroxide>
A nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention is a positive electrode active material composed of secondary particles in which primary particles containing nickel, manganese, and cobalt are aggregated, or the primary particles and the secondary particles. is a precursor of

And the sodium content contained in the nickel-manganese-cobalt composite hydroxide is less than 0.0005% by mass, and the porosity of the particles of the nickel-manganese-cobalt composite hydroxide is 20 to 50%. Characterized by A nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention will be specifically described below.

[Particle composition]
The nickel-manganese-cobalt composite hydroxide has a composition represented by the general formula: Ni _{x Mny} Co _z M _t (OH) _{2 + a} (where x + y + z + t = 1, 0.20 ≤ x ≤ 0.80, 0.10 ≤ y ≤ 0.90, 0.10 ≤ z ≤ 0.50, 0 ≤ t ≤ 0.10, 0 ≤ a ≤ 0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, one or more of Mo and W).

In the above general formula, x indicating the nickel content is preferably 0.20≦x≦0.80. Further, x indicating the nickel content is more preferably x≦0.6 in consideration of electrical properties and thermal stability.

Moreover, y indicating the manganese content is preferably 0.10≦y≦0.90. When manganese is added in this range, the durability and safety of the battery can be further improved when used as the positive electrode active material of the battery. When y is less than 0.10, it is not possible to sufficiently obtain the effect of improving durability and safety of the battery. is not preferable because it may decrease

In the above general formula, z, which indicates the cobalt content, is preferably 0.10≦z≦0.50. By adding an appropriate amount of cobalt, it is possible to improve the cycle characteristics and reduce the expansion and contraction behavior of the crystal lattice due to the desorption/insertion of Li during charging and discharging. It is not preferable because it is difficult to sufficiently obtain the effect of reducing the On the other hand, if the amount of cobalt added is too large and z exceeds 0.5, the initial discharge capacity may decrease significantly, and furthermore, there is a problem of being disadvantageous in terms of cost, which is not preferable.

The additive element M is one or more of Mg, Al, Ca, Ti, V, Cr, Zr, Nb, Mo, and W, and is added in order to improve battery characteristics such as cycle characteristics and output characteristics. It is. t, which indicates the content of the additional element M, preferably satisfies 0≦t≦0.10. If t exceeds 0.1, the amount of metal elements that contribute to the Redox reaction may decrease, and the battery capacity may decrease, which is not preferable.

In addition, the analysis method for the composition of the particles is not particularly limited, but it can be obtained from a chemical analysis method such as acid decomposition-ICP emission spectrometry.

[Particle structure]
A nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention is composed of secondary particles in which a plurality of primary particles are aggregated, or both of the primary particles and secondary particles. The shape of the primary particles that make up the secondary particles can take various shapes such as plate-like, needle-like, rectangular parallelepiped, elliptical, and rhombohedral shapes. In addition, the aggregation state of a plurality of primary particles can also be applied to the present invention, in addition to the case where the primary particles are aggregated in random directions, and the case where the major diameter direction of the particles is aggregated radially from the center.

As for the aggregation state, it is preferable that plate-like or needle-like primary particles aggregate in random directions to form secondary particles. In the case of such a structure, almost uniform voids are generated between the primary particles, and when mixed with the lithium compound and fired, the molten lithium compound spreads throughout the secondary particles, and lithium diffuses sufficiently. for it will be

Although the method for observing the shapes of the primary particles and secondary particles is not particularly limited, they can be measured by observing a cross section of the nickel-manganese-cobalt composite hydroxide using a scanning electron microscope (SEM) or the like.

[Particle internal structure]
A nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention has a hollow structure inside secondary particles. The nickel-manganese-cobalt composite hydroxide, which has this hollow structure, is used as a precursor of the lithium metal composite oxide. Excellent for

By the way, "having a hollow structure inside the secondary particle" refers to a structure composed of a hollow portion which is a space in the center of the secondary particle and an outer shell portion outside the hollow portion. As shown in FIG. 1, this hollow structure can be confirmed by observing the cross section of nickel-manganese-cobalt composite hydroxide and lithium metal composite oxide with a scanning electron microscope, as shown in the cross-sectional SEM image. .

In addition, the nickel-manganese-cobalt composite hydroxide having a hollow structure preferably has a porosity of 10 to 90%, more preferably 20 to 50%, as measured by cross-sectional observation of the particles. preferable. In addition, the lithium metal composite oxide having a hollow structure also preferably has a porosity of 10 to 90%, more preferably 20 to 50%, as measured by cross-sectional observation of the particles. As a result, the contact area between the positive electrode active material and the electrolyte can be made sufficient while maintaining the particle strength within an allowable range without excessively reducing the bulk density of the obtained positive electrode active material, and the battery characteristics can be improved.

In addition, in the present invention, the nickel-manganese-cobalt composite hydroxide and the lithium-metal composite oxide have a hollow structure. For example, by adjusting the crystallization conditions during the manufacturing process for metal composite hydroxides that serve as a supply source of transition metals such as nickel, manganese, and cobalt during mixing and firing, solid structures and hollow structures can be obtained. It is also possible to mix structures and porous structures in combination and proportions, and the obtained metal composite oxide is better than simply mixing solid, hollow, and porous products. This has the advantage of stabilizing the overall composition and particle size.

[Average particle size (MV)]
The nickel-manganese-cobalt composite hydroxide is preferably adjusted to have an average particle size of 3 to 20 μm. If the average particle size is less than 3 μm, the packing density of the particles may decrease when the positive electrode is formed, and the battery capacity per volume of the positive electrode may decrease, which is not preferable. On the other hand, if the average particle diameter exceeds 20 μm, the specific surface area of the positive electrode active material is reduced, and the interface with the electrolyte solution of the battery is reduced, which may increase the resistance of the positive electrode and reduce the output characteristics of the battery. I don't like it because Therefore, if the nickel-manganese-cobalt composite hydroxide is adjusted to have an average particle size of 3 to 20 μm, preferably 3 to 15 μm, more preferably 4 to 12 μm, this positive electrode active material can be used as a positive electrode material. In the lithium ion secondary battery, the battery capacity per volume can be increased, the safety is high, and the cycle characteristics are good.

Also, the method for measuring the average particle diameter is not particularly limited, but for example, it can be obtained from the volume standard distribution measured using the laser diffraction/scattering method.

[Impurity content]
Generally, nickel-manganese-cobalt composite hydroxide contains sulfate group, chlorine group and sodium as impurities. Since these impurities cause deterioration of the reaction with lithium and hardly contribute to the charge/discharge reaction, it is preferable to remove them as much as possible and reduce their content. Conventionally, techniques for removing those impurities have been disclosed, but they are still insufficient.

Therefore, the sodium content contained in the nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention is characterized by being less than 0.0005% by mass. In this way, it is possible to reliably reduce the sodium content and provide a nickel-manganese-cobalt composite hydroxide that is a precursor of a positive electrode active material for a lithium-ion secondary battery capable of improving battery characteristics. can.

In addition, it is preferable that the nickel-manganese-cobalt composite hydroxide has a sulfate group content of 0.2% by mass or less and a chlorine group content of 0.01% by mass or less. In this way, the nickel-manganese-cobalt composite hydroxide, which is a precursor of the positive electrode active material of a lithium ion secondary battery, can reliably reduce the contents of sulfate radicals, chlorine radicals and sodium, and can improve battery characteristics. can provide things.

The content of each impurity can be obtained, for example, using the analysis method shown below. Sodium can be determined by acid decomposition-atomic absorption spectrometry, acid decomposition-ICP emission spectrometry, or the like. In addition, the total sulfur content of the nickel-manganese-cobalt composite hydroxide is analyzed by the combustion infrared absorption method, the acid decomposition-ICP emission spectroscopic analysis method, etc., and the total sulfur content is determined by the sulfuric acid radical (SO ₄ ^2- ). In addition, the chlorine root can be obtained by separating the chlorine root contained in the nickel-manganese-cobalt composite hydroxide directly or by distillation in the form of silver chloride or the like and analyzing it by X-ray fluorescence (XRF) analysis. I can.

[Particle size distribution]
The nickel-manganese-cobalt composite hydroxide is preferably adjusted so that [(d90-d10)/average particle diameter], which is an index showing the spread of the particle size distribution of the particles, is 0.55 or less.

If the particle size distribution is wide and [(d90-d10)/average particle size], which is an index showing the spread of the particle size distribution, exceeds 0.55, the particle size is larger than the average particle size. A large number of very small fine particles and particles (large-diameter particles) with a particle diameter that is extremely large relative to the average particle diameter are likely to exist.

Such characteristics of the particle size distribution in the precursor stage also greatly affect the positive electrode active material obtained after the firing process. When a positive electrode is formed using a positive electrode active material containing a large amount of fine particles, heat may be generated due to local reactions of the fine particles. is selectively deteriorated, and the cycle characteristics may be deteriorated, which is not preferable. On the other hand, when the positive electrode is formed using a positive electrode active material in which many large particles are present, the reaction area between the electrolyte and the positive electrode active material cannot be sufficiently obtained, and the reaction resistance increases, resulting in a decrease in battery output. It is not preferred because there are cases.

Therefore, in the particle size distribution of the precursor nickel-manganese-cobalt composite hydroxide, [(d90-d10)/average particle size] is preferably 0.55 or less, and fine particles or Since the ratio of large-diameter particles is reduced, a lithium ion secondary battery using this positive electrode active material for the positive electrode is more excellent in safety, and can obtain good cycle characteristics and battery output.

In the index [(d90-d10)/average particle size] indicating the spread of the particle size distribution, d10 is the total volume of all particles when the number of particles in each particle size is accumulated from the smaller particle size. means the particle size that is 10% of the On the other hand, d90 means the particle size at which the cumulative volume becomes 90% of the total volume of all particles when the number of particles in each particle size is accumulated from the smaller particle size. Methods for determining the average particle size, d90, and d10 are not particularly limited, but they can be determined, for example, from a volume standard distribution measured using a laser diffraction/scattering method.

[Specific surface area]
The nickel-manganese-cobalt composite hydroxide is preferably adjusted to have a specific surface area of 10 to 80 m ² /g. For stability, it is more preferably adjusted to 10 to 20 m ² /g. If the specific surface area is within the above range, a sufficient surface area of the particles that can come into contact with the molten lithium compound can be ensured when mixed with the lithium compound and fired, and the particle strength of the positive electrode active material can be satisfied. be.

On the other hand, when the specific surface area is less than 10 m ² /g, the contact with the molten lithium compound becomes insufficient when mixed with the lithium compound and fired, and the crystallinity of the resulting lithium-nickel-manganese-cobalt composite oxide decreases. However, when constructing a lithium ion secondary battery as a positive electrode material, there is a concern that the diffusion of lithium in the solid phase is hindered and the capacity decreases. In addition, when the specific surface area exceeds 80 m ² /g, when mixed with a lithium compound and fired, crystal growth proceeds too much, and nickel is mixed in the lithium layer of the lithium-transition metal composite oxide, which is a layered compound. may occur and the charge/discharge capacity may decrease, which is not preferable.

Furthermore, like the nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention, if it has a hollow structure with a space in the center of the secondary particles, the specific surface area will be 30 to 40 m ² /g. It is more preferable that they are adjusted in the same manner. If the specific surface area is less than 30 m ² /g, it is difficult to obtain a predetermined porosity, and a sufficient reaction area with the lithium compound cannot be secured during firing. If the specific surface area exceeds 40 m ² /g, the fillability may deteriorate when the positive electrode active material has a hollow structure.

The method for measuring the specific surface area is not particularly limited, but it can be obtained, for example, by a BET multi-point method, a BET single-point method, a nitrogen gas adsorption/desorption method, or the like.

FIG. 1 shows a cross-sectional SEM photograph of a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention. Thus, the nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention has a hollow internal structure as shown in FIG.

According to the nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention, it is a positive electrode active material precursor for a lithium ion secondary battery that can reliably reduce the sodium content and improve the battery characteristics. can provide.

<2. Lithium Nickel Manganese Cobalt Composite Oxide>
A lithium-nickel-manganese-cobalt composite oxide according to an embodiment of the present invention is composed of secondary particles in which primary particles containing lithium, nickel, manganese, and cobalt are aggregated, or the primary particles and the secondary particles. The sodium content in the lithium-nickel-manganese-cobalt composite oxide is less than 0.0005% by mass, and the sodium content in the lithium-nickel-manganese-cobalt composite oxide is less than 0.0005% by mass, The lithium-nickel-manganese-cobalt composite oxide has a porosity of 20 to 50%.

Further, the lithium-nickel-manganese-cobalt composite oxide has a sulfate group content of 0.15% by mass or less, a chlorine group content of 0.005% by mass or less, and a Me site occupancy of 93.0% or more. Preferably.

The above nickel-manganese-cobalt composite hydroxide can be mixed with a lithium compound and fired to produce a lithium-nickel-manganese-cobalt composite oxide. The above lithium-nickel-manganese-cobalt composite oxide can be used as a raw material for a positive electrode active material for lithium-ion secondary batteries.

The lithium-nickel-manganese-cobalt composite oxide used as the positive electrode active material includes a precursor nickel-manganese-cobalt composite hydroxide, lithium carbonate (Li ₂ CO ₃ : melting point 723° C.), and lithium hydroxide (LiOH: melting point 462° C.). ° C.), lithium nitrate (LiNO ₃ : melting point 261° C.), lithium chloride (LiCl: melting point 613° C.), and lithium sulfate (Li ₂ SO ₄ : melting point 859° C.). obtained through time.

Regarding the lithium compound, it is particularly preferable to use lithium carbonate or lithium hydroxide in consideration of ease of handling and stability of quality.

In this baking step, carbonate groups, hydroxyl groups, nitrate groups, chlorine groups, and sulfate groups, which are constituents of the lithium compound, are volatilized, but a very small portion remains in the positive electrode active material. In addition, non-volatile components such as sodium, particle size distribution, specific surface area, and the hollow structure of the secondary particles almost inherit the characteristics of the precursor nickel-manganese-cobalt composite hydroxide.

According to the lithium-nickel-manganese-cobalt composite oxide according to one embodiment of the present invention, a lithium-ion secondary battery capable of further improving the battery characteristics by surely reducing the sodium content and increasing the porosity can be produced. A positive electrode active material can be provided.

<3. Method for producing nickel-manganese-cobalt composite hydroxide>
Next, a method for producing a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention will be described with reference to FIG. A method for producing a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention is composed of secondary particles in which primary particles containing nickel, manganese, and cobalt are aggregated, or the primary particles and the secondary particles, This is a method for producing a precursor of a positive electrode active material. Then, as shown in FIG. 2, it has a crystallization step S10 and a washing step S20.

In the crystallization step S10, the transition metal composite hydroxide is crystallized in a reaction solution obtained by adding a raw material solution containing nickel, manganese, and cobalt, a solution containing an ammonium ion donor, and an alkaline solution. get Then, in the washing step S20, the transition metal composite hydroxide obtained in the crystallization step S10 is washed with a washing liquid.

Further, the alkaline solution in the crystallization step S10 is a mixed solution of an alkali metal hydroxide and a carbonate, and the molar ratio of the carbonate to the alkali metal hydroxide in the mixed solution is [CO ₃ ²⁻ ]/[OH ⁻ ] is 0.002 to 0.050, and in the crystallization step S10, crystallization is performed by switching the atmosphere between an oxidizing atmosphere and a non-oxidizing atmosphere, followed by the washing. The cleaning liquid in step S20 is characterized by being an ammonium hydrogen carbonate solution having a concentration of 0.05 mol/L or more. Each step will be described in detail below.

<3-1. Crystallization process>
In the crystallization step S10, the transition metal composite hydroxide is crystallized in a reaction solution obtained by adding a raw material solution containing nickel, manganese, and cobalt, a solution containing an ammonium ion donor, and an alkaline solution. get

Moreover, the crystallization step S10 preferably further includes a nucleation step S11 and a grain growth step S12. In the nucleation step S11, an alkaline solution is added and nuclei are generated in the reaction solution so that the pH measured at a liquid temperature of 25° C. is 12.0 to 14.0. It is preferable to add an alkaline solution to the reaction solution containing the nuclei formed in step S11 so that the pH is 10.5 to 12.0 when measured at a liquid temperature of 25°C. Details will be described later.

In the conventional continuous crystallization method, the nucleation reaction and the nucleation growth reaction proceed simultaneously in the same reaction vessel, so the particle size distribution of the obtained precursor is wide. On the other hand, in the method for producing a nickel-manganese-cobalt composite hydroxide according to the present invention, the time during which the nucleation reaction mainly occurs (nucleation step) and the time during which the particle growth reaction occurs mainly (particle growth step) are clearly defined. By separating, even if both steps are performed in the same reactor, a transition metal composite hydroxide having a narrow particle size distribution can be obtained. Further, by using a mixed solution of an alkali metal hydroxide and a carbonate as the alkaline solution, impurities such as sulfate groups can be reduced.

Materials and conditions used in the method for producing a nickel-manganese-cobalt composite hydroxide according to the present invention are described in detail below.

[Raw material solution containing nickel, manganese and cobalt]
Metal salts such as nickel salts, manganese salts, and cobalt salts used in the raw material solution containing nickel, manganese, and cobalt are not particularly limited as long as they are water-soluble compounds. You can use things. For example, nickel sulfate, manganese sulfate, and cobalt sulfate are preferably used.

In addition, if necessary, compounds containing one or more additive elements M can be mixed at a predetermined ratio to prepare a raw material solution. In the crystallization step S10 in this case, it is preferable to use a compound containing one or more of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo and W. Titanium sulfate, ammonium peroxotitanate , potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, zirconium nitrate, niobium oxalate, ammonium molybdate, sodium tungstate, and ammonium tungstate.

Further, the nickel-manganese-cobalt composite hydroxide obtained by crystallization is mixed with an aqueous solution containing one or more additional elements M to form a slurry, and the pH is adjusted to obtain one or more additional elements M. The compound may coat the nickel-manganese-cobalt composite hydroxide.

The concentration of the raw material solution is preferably 1.0 to 2.6 mol/L, more preferably 1.0 to 2.2 mol/L in total of the metal salts. If it is less than 1.0 mol/L, the obtained hydroxide slurry concentration is low, resulting in poor productivity. On the other hand, if it exceeds 2.6 mol/L, crystal precipitation or freezing occurs at -5°C or lower, which may clog the pipes of the equipment, and the pipes must be kept warm or heated, which increases costs.

Furthermore, the amount of the raw material solution supplied to the reaction tank is preferably such that the concentration of the crystallized substance at the time of finishing the crystallization reaction is approximately 30 to 250 g/L, preferably 80 to 150 g/L. . If the crystallized substance concentration is less than 30 g/L, the aggregation of the primary particles may be insufficient, and if it exceeds 250 g/L, the mixed aqueous solution to be added may not diffuse sufficiently in the reactor. However, the grain growth may be biased.

[Ammonium ion donor]
The ammonium ion donor in the reaction solution is not particularly limited as long as it is a water-soluble compound, and ammonia water, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc. can be used. Ammonium sulfate is preferably used.

The ammonium ion concentration in the reaction solution is adjusted to preferably 3 to 25 g/L, more preferably 5 to 20 g/L, still more preferably 5 to 15 g/L. Due to the presence of ammonium ions in the reaction solution, metal ions, especially nickel ions, form an ammine complex, increasing the solubility of metal ions, promoting the growth of primary particles, and producing a dense nickel-manganese-cobalt composite hydroxide. Particles are easily obtained. Furthermore, since the solubility of metal ions is stabilized, it is easy to obtain nickel-manganese-cobalt composite hydroxide particles having a uniform shape and particle size. By setting the ammonium ion concentration in the reaction solution to 3 to 25 g/L, it is easy to obtain composite hydroxide particles that are denser and have a uniform shape and particle size.

If the ammonium ion concentration in the reaction solution is less than 3 g/L, the solubility of metal ions may become unstable, and primary particles with uniform shape and particle size may not be formed, resulting in the formation of gel-like nuclei. may result in a broader particle size distribution. On the other hand, if the ammonium ion concentration exceeds 25 g/L, the solubility of metal ions becomes too high, and the amount of metal ions remaining in the reaction solution increases, which may cause composition deviation. The concentration of ammonium ions can be measured by an ion electrode method (ion meter).

[Alkaline solution]
The alkaline solution is prepared with a mixed solution of alkali metal hydroxide and carbonate. The alkaline solution has a [CO ₃ ²⁻ ]/[OH ⁻ ] ratio of 0.002 to 0.050, which represents the molar ratio of alkali metal hydroxide to carbonate. Further, it is more preferably 0.005 to 0.030, and even more preferably 0.010 to 0.025.

By using a mixed solution of an alkali metal hydroxide and a carbonate as the alkaline solution, anions such as sulfate radicals and chlorine radicals remaining as impurities in the nickel-manganese-cobalt composite hydroxide obtained in the crystallization step S10 are removed. , can be removed by substitution with carbonate radicals. Compared to sulfate radicals and chlorine radicals, carbonate radicals are more likely to volatilize by heating. It hardly remains in the lithium-nickel-manganese-cobalt composite oxide that is the positive electrode material.

If [CO ₃ ²⁻ ]/[OH ⁻ ] is less than 0.002, in the crystallization step S10, the substitution of the raw material-derived impurities such as sulfate groups and chlorine for carbonate ions becomes insufficient, and these impurities are removed. It becomes easier to incorporate into the nickel-cobalt-manganese composite hydroxide. On the other hand, even if [CO ₃ ²⁻ ]/[OH ⁻ ] exceeds 0.050, the reduction of sulfuric acid radicals and chlorine, which are impurities derived from raw materials, does not change, and excessively added carbonate increases the cost. .

The alkali metal hydroxide is preferably one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide, and a compound that is easily dissolved in water is preferable because the amount added is easy to control.

The carbonate is preferably one or more of sodium carbonate, potassium carbonate, and ammonium carbonate, and a compound that is easily dissolved in water is preferable because the amount added is easy to control.

In addition, the method of adding the alkaline solution to the reaction tank is not particularly limited. do it.

[pH control]
In the crystallization step S10, an alkaline solution is added to generate nuclei so that the pH of the reaction solution measured at a liquid temperature of 25° C. is 12.0 to 14.0; An alkaline solution is added to the particle growth solution containing the nuclei formed in the nucleation step S11 so that the pH measured at a liquid temperature of 25° C. is 10.5 to 12.0, thereby removing the nuclei. It is more preferable to consist of a grain growth step S12 for growing.

In other words, the nucleation reaction and the particle growth reaction do not proceed at the same time in the same tank, but the time for mainly the nucleation reaction (nucleation step S11) and the time for mainly the particle growth reaction (particle growth step S12) is characterized by a clear separation of the time at which The nucleation step S11 and the grain growth step S12 are described in detail below.

<3-1-1. Nucleation step>
In the nucleation step S11, it is preferable to control the pH of the reaction solution to be in the range of 12.0 to 14.0 at a liquid temperature of 25.degree. If the pH exceeds 14.0, the generated nuclei may become too fine and the reaction solution may gel. Further, if the pH is less than 12.0, a growth reaction of nuclei occurs together with nucleation, so that the range of particle size distribution of the nuclei formed may become wide and non-uniform.

That is, in the nucleation step S11, by controlling the pH of the reaction solution in the range of 12.0 to 14.0, the growth of nuclei can be suppressed and only nucleation can occur, and the nuclei formed can also be homogeneous and have a narrower range of particle size distribution.

<3-1-2. Particle Growth Process>
In the particle growth step S12, the pH of the reaction solution is preferably 10.5 to 12.0, more preferably 11.0 to 12.0, based on the liquid temperature of 25°C. If the pH exceeds 12.0, the number of newly generated nuclei increases and fine secondary particles are generated, so that a hydroxide with a good particle size distribution may not be obtained. Further, when the pH is less than 10.5, the solubility of ammonium ions is high, and the amount of metal ions that remain in the liquid without precipitating increases, which may deteriorate the production efficiency.

That is, in the particle growth step S12, by controlling the pH of the reaction solution in the range of 10.5 to 12.0, only the growth of the nuclei generated in the nucleation step S11 is preferentially caused, and new nucleation is generated. can be suppressed, and the resulting nickel-cobalt-manganese composite hydroxide can be made homogeneous and have a narrower range of particle size distribution.

When the pH is 12.0, it is a boundary condition between nucleation and nucleus growth, so depending on the presence or absence of nuclei present in the reaction solution, either the nucleation step or the particle growth step can be set. can be done. That is, if the pH in the nucleation step S11 is set higher than 12.0 to generate a large amount of nuclei, and then the pH is set to 12.0 in the particle growth step S12, a large amount of nuclei are present in the reaction aqueous solution. growth occurs preferentially, and the hydroxide having a narrower particle size distribution and a relatively large particle size is obtained.

On the other hand, when there are no nuclei in the reaction solution, that is, when the pH is set to 12.0 in the nucleation step S11, there are no growing nuclei, so nucleation occurs preferentially, and the particle growth step By making the pH of S12 lower than 12.0, the generated nuclei grow to obtain a better hydroxide.

In any case, the pH in the particle growth step S12 may be controlled at a value lower than the pH in the nucleation step S11. , preferably lower than the pH of the nucleation step S11 by 0.5 or more, more preferably by 1.0 or more.

As described above, by clearly separating the nucleation step S11 and the particle growth step S12 by pH, the nucleation occurs preferentially in the nucleation step S11, and the growth of nuclei hardly occurs. Only nucleus growth occurs in step S12, and almost no new nuclei are generated. As a result, in the nucleation step S11, uniform nuclei having a narrow particle size distribution range can be formed, and in the particle growth step S12, nuclei can be grown homogeneously. Therefore, in the method for producing nickel-manganese-cobalt composite hydroxide, uniform nickel-manganese-cobalt composite hydroxide particles with a narrower range of particle size distribution can be obtained.

[Reaction solution temperature]
In the reaction tank, the temperature of the reaction solution is preferably set at 20-80°C, more preferably 30-70°C, and still more preferably 35-60°C. If the temperature of the reaction solution is lower than 20° C., the solubility of metal ions is low, so nuclei are likely to occur and control becomes difficult. On the other hand, if the temperature exceeds 80° C., volatilization of ammonia is accelerated, so an excess ammonium ion donor must be added in order to maintain a predetermined ammonia concentration, resulting in high cost.

[Reaction atmosphere]
The particle size and particle structure of the nickel-cobalt-manganese composite hydroxide are also controlled by the reaction atmosphere in the crystallization step S10. Therefore, in the crystallization step S10 in the method for producing a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention, crystallization is performed by switching the atmosphere between two stages of an oxidizing atmosphere and a non-oxidizing atmosphere. Specifically, crystallization is performed in an oxidizing atmosphere, and then crystallization is performed by switching the atmosphere in the reaction vessel to a non-oxidizing atmosphere.

When the atmosphere in the reaction vessel during the crystallization step S10 is controlled to be a non-oxidizing atmosphere, the growth of the primary particles forming the nickel-cobalt-manganese composite hydroxide is promoted, the primary particles are large and dense, and the particle size is small. Moderately large secondary particles are formed. On the other hand, when the atmosphere in the reaction vessel during the crystallization process is controlled to an oxidizing atmosphere, the growth of the primary particles forming the nickel-cobalt-manganese composite hydroxide is suppressed, and the primary particles consist of fine primary particles, leaving a space in the center of the particles. Alternatively, secondary particles in which a large number of fine voids are dispersed are formed.

In the method for producing a nickel-manganese-cobalt composite hydroxide according to one embodiment of the present invention, in the crystallization step S10, crystallization is performed by switching between two stages of an oxidizing atmosphere and a non-oxidizing atmosphere. By adjusting the timing of switching the atmosphere, it is possible to control the size of the hollow portion of the particles when forming a hollow structure and the ratio of void portions when forming a porous structure.

By the way, the non-oxidizing atmosphere refers to a mixed atmosphere of oxygen having an oxygen concentration of 5.0% by volume or less, preferably 2.5% by volume or less, more preferably 1.0% by volume or less, and an inert gas. As a means for maintaining the interior space of the reaction vessel in such a non-oxidizing atmosphere, an inert gas such as nitrogen is passed through the interior space of the reaction vessel, and the inert gas is bubbled into the reaction solution. It is mentioned that The flow rate of bubbling in the crystallization step S10 is preferably 3 to 7 L/min, more preferably about 5 L/min.

On the other hand, an oxidizing atmosphere means an atmosphere in which the oxygen concentration exceeds 5.0% by volume, preferably 10.0% by volume or more, and more preferably 15.0% by volume or more. Means for maintaining the space in the reaction vessel in such an oxidizing atmosphere include circulating air or the like into the space in the reaction vessel or bubbling the air or the like into the reaction solution.

In the case of building a hollow structure, the atmosphere in the reaction vessel is set to an oxidizing atmosphere (usually, an oxygen concentration exceeding 21% by volume, such as an air atmosphere), and the crystallization treatment is carried out, for example, within 0.5 hours, It is preferable to stop the crystallization treatment by stopping the liquid supply after a predetermined time. Thereafter, the atmosphere is switched to an inert atmosphere or a non-oxidizing atmosphere in which the oxygen concentration is controlled to 0.2% by volume or less, and the crystallization treatment is performed within the range of 0.5 to 3.5 hours to change the crystallization state. Thus, it is preferable to produce a nickel-manganese-cobalt composite hydroxide having a porous structure by controlling the porosity of the obtained metal composite hydroxide to 20 to 50%. The total crystallization time is in the range of 0.5 to 4 hours, and is appropriately adjusted depending on the size of the hydroxide particles, the size of the hollow, the thickness of the outer shell, and the like.

By controlling the atmosphere in the reaction vessel to a non-oxidizing atmosphere or an oxidizing atmosphere in this way, the porosity of the secondary particles in the resulting metal composite hydroxide can be controlled.

Although the nucleus generation step S11 and the grain growth step S12 have been described above, the reaction atmosphere is simultaneously controlled while the nucleation and grain growth are being performed.

[Porosity]
After the nickel-manganese-cobalt composite hydroxide is embedded in the resin, a cross-section polisher (CP) is used to cut the particles of the nickel-manganese-cobalt composite hydroxide by argon sputtering to expose the cross section of the particles. The exposed grain cross section is observed using a scanning electron microscope, and the image of the observed grain cross section is analyzed by image analysis software, with the void portions of the image being black and the dense portions being white. The porosity can be obtained by calculating the area of black portion/(black portion+white portion) with respect to cross sections of at least one particle.

<2-2. Washing process>
In the washing step S20, the transition metal composite hydroxide obtained in the crystallization step S10 is washed with a washing liquid.

[Washing liquid type]
In the cleaning step S20, cleaning is performed with a cleaning liquid based on carbonate, hydrogen carbonate (bicarbonate), alkali metal salt or ammonium salt of hydroxide. Preferably, the transition metal composite hydroxide is washed with a washing solution prepared by dissolving carbonate, hydrogen carbonate (bicarbonate), or a mixture thereof in water.

By doing so, anions such as sulfate radicals and chlorine radicals, which are impurities, can be efficiently removed by utilizing substitution reactions with carbonate ions and hydrogen carbonate ions (bicarbonate ions) in the cleaning solution. I can. In addition, by using a carbonate or a hydrogen carbonate (bicarbonate), contamination with an alkali metal such as sodium can be suppressed as compared with the case of using a hydroxide. In addition, in transition metal composite hydroxides having a void structure, when hydroxides are used, it is difficult to remove impurities inside the particles. ) is more effective.

Sodium carbonate, potassium carbonate and ammonium carbonate are preferably selected as carbonates, and sodium hydrogen carbonate, potassium hydrogen carbonate and ammonium hydrogen carbonate are preferably selected as hydrogen carbonates (bicarbonates). In addition, by selecting an ammonium salt from carbonates and hydrogen carbonates (bicarbonates), cations such as sodium, which are impurities, can be efficiently removed by using a substitution reaction with ammonium ions in the cleaning solution. can be removed. Furthermore, cations such as sodium can be removed most efficiently by selecting ammonium hydrogen carbonate (ammonium bicarbonate) among ammonium salts.

This is because, in addition to the substitution reaction between cations such as sodium and ammonium ions, in addition to this, ammonium bicarbonate (ammonium bicarbonate) has properties superior to other salts, that is, when it is used as a cleaning solution. It is considered that the high foaming efficiency of carbon dioxide gas contributes greatly to the removal of cations such as sodium.

[Concentration and pH]
The concentration of the ammonium bicarbonate solution, which is the cleaning liquid, is set to 0.05 mol/L or more. If the concentration is less than 0.05 mol/L, the effect of removing impurities such as sulfate groups, chlorine groups, and sodium may decrease. Also, if the concentration is 0.05 mol/L or more, the effect of removing these impurities does not change. Therefore, if ammonium bicarbonate (ammonium bicarbonate) is excessively added, it will increase the cost and affect the environmental load such as the waste water standard, so it is preferable to set the upper limit concentration to about 1.0 mol/L.

The pH of the ammonium bicarbonate solution does not need to be adjusted as long as the concentration is 0.05 mol/L or more, and the pH may be used as it is. If the concentration is 0.05-1.0 mol/L, the pH will be in the range of approximately 8.0-9.0.

[Liquid temperature]
The liquid temperature of the ammonium hydrogen carbonate solution, which is the cleaning liquid, is not particularly limited, but is preferably 15 to 50°C. If the liquid temperature is within the above range, the substitution reaction with impurities and the bubbling effect of carbon dioxide gas generated from ammonium hydrogen carbonate are more favorable, and the removal of impurities proceeds efficiently.

[Liquid volume]
The amount of the ammonium bicarbonate solution, which is the cleaning liquid, is preferably 1 to 20 L per 1 kg of the nickel-manganese-cobalt composite hydroxide (the slurry concentration is 50 to 1000 g/L). If it is less than 1 L, a sufficient effect of removing impurities may not be obtained. In addition, even if the amount of liquid exceeds 20 L, the effect of removing impurities does not change, and an excessive amount of liquid increases the cost and affects the environmental load such as wastewater standards, which is a factor in increasing the load of wastewater in wastewater treatment. It also becomes.

[Washing time]
The washing time with the ammonium bicarbonate solution is not particularly limited as long as the impurities can be sufficiently removed, but it is usually 0.5 to 2 hours.

[Washing method]
As a washing method, 1) a general washing method of adding nickel-manganese-cobalt composite hydroxide to an ammonium hydrogencarbonate solution, making it into a slurry, stirring and washing, and then filtering, or 2) neutralization and crystallization. The slurry containing the nickel-manganese-cobalt composite hydroxide produced by is supplied to a filter such as a filter press, and an ammonium bicarbonate solution is passed through for washing. Liquid washing is more preferable because it is highly effective in removing impurities, and filtration and washing can be continuously performed in the same facility, resulting in high productivity.

After washing with the ammonium bicarbonate solution, the nickel-manganese-cobalt composite hydroxide may be adhered to the washing liquid containing impurities washed out by the substitution reaction, so it is preferable to wash with water at the end. Furthermore, after washing with water, it is preferable to perform a drying step (not shown) for drying the filtered water adhering to the nickel-manganese-cobalt composite hydroxide.

The nickel-manganese-cobalt composite hydroxide obtained through the washing step S20 is a positive electrode composed of secondary particles in which primary particles containing nickel, manganese, and cobalt are aggregated, or the primary particles and the secondary particles. A nickel-manganese-cobalt composite hydroxide that is a precursor of an active material, wherein the sodium content in the nickel-manganese-cobalt composite hydroxide is less than 0.0005% by mass, and the nickel-manganese-cobalt composite hydroxide The porosity of the particles is 20 to 50%.

According to the method for producing a nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention, it is possible to reliably reduce the content of sodium in particular and improve the battery characteristics of a positive electrode active material for a lithium-ion secondary battery. A method for producing nickel-manganese-cobalt composite hydroxide, which is a precursor, can be provided.

Next, the nickel-manganese-cobalt composite hydroxide, the method for producing the nickel-manganese-cobalt composite hydroxide, and the lithium-nickel-manganese-cobalt composite oxide according to one embodiment of the present invention will be described in detail with reference to examples. However, the present invention is not limited to these examples.

For Examples 1 to 13 and Comparative Examples 1 to 9, the transition metal composite hydroxide obtained in the crystallization step was washed, filtered, and dried to recover nickel-manganese-cobalt composite hydroxide as a precursor. After that, various analyzes were performed by the following methods.

[composition]
The composition was analyzed by acid decomposition-ICP emission spectrometry, and the measurement was performed using ICPE-9000 (manufactured by Shimadzu Corporation), which is a multi-type ICP emission spectrometer.

[Sodium content]
The sodium content was analyzed by acid decomposition-atomic absorption spectrometry, using an atomic absorption spectrophotometer 240AA (manufactured by Agilent Technologies) for measurement.

[Sulfate group content]
The sulfate radical content was obtained by analyzing the total sulfur content by acid decomposition-ICP emission spectrometry and converting the total sulfur content into sulfate radical (SO ₄ ²⁻ ). For the measurement, ICPE-9000 (manufactured by Shimadzu Corporation), which is a multi-type ICP emission spectrometer, was used.

[Chlorine root content]
Chlorine root content was analyzed by X-ray fluorescence spectroscopy (XRF) by separating the chlorine root contained in the sample directly or by a distillation operation in the form of silver chloride. For the measurement, Axios (manufactured by Spectris Co., Ltd.), which is a fluorescent X-ray analyzer, was used.

[Average particle size and particle size distribution]
The average particle size (MV) and the particle size distribution [(d90-d10)/average particle size] were obtained from the volume standard distribution measured using a laser diffraction/scattering method. For the measurement, Microtrac MT3300EXII (manufactured by Microtrac Bell Co., Ltd.), which is a laser diffraction/scattering particle size distribution analyzer, was used.

[Specific surface area]
The specific surface area was analyzed by the nitrogen gas adsorption/desorption method based on the BET one-point method, and the gas flow type specific surface area measuring device Macsorb 1200 series (manufactured by Mountech Co., Ltd.) was used for the measurement.

[Porosity]
The porosity was measured by using a cross section polisher IB-19530CP (manufactured by JEOL Ltd.), which is a cross section preparation device, for cutting the sample particles, and for observing the cross section, using a Schottky field emission scanning. A type electron microscope SEM-EDS, JSM-7001F (manufactured by JEOL Ltd.) was used. Furthermore, using WinRoof 6.1.1 (manufactured by Mitani Shoji Co., Ltd.), which is an image analysis and measurement software, the void part of the particle cross section is measured as black, and the dense part of the particle is measured as white, and any 20 or more The porosity was obtained by calculating the area of black portion/(black portion+white portion) for the particles.

[Manufacturing and Evaluation of Positive Electrode Active Material]
In addition, a lithium metal composite oxide, more specifically a lithium nickel manganese cobalt composite oxide, which is a positive electrode active material using the nickel manganese cobalt composite hydroxide of the present invention as a raw material, is produced and evaluated by the following method. did

[A, production of positive electrode active material]
The precursor nickel-manganese-cobalt composite hydroxide was heat-treated at 700° C. for 6 hours in an air stream (oxygen: 21% by volume) to recover the metal composite oxide. Subsequently, lithium hydroxide, which is a lithium compound, was weighed so that Li 2 /Me=1.025, and mixed with the recovered metal composite oxide to prepare a lithium mixture. For the mixing operation, a shaker mixer device (TURBULA-Type T2C manufactured by Willie & Bacchofen (WAB)) was used.

Next, the prepared lithium mixture is calcined at 500° C. for 4 hours in an oxygen (oxygen: 100% by volume) stream, further calcined at 730° C. for 24 hours, cooled and then pulverized to obtain lithium nickel manganese cobalt. A composite oxide was obtained.

[B, Evaluation of Positive Electrode Active Material]
The above-described analytical method and analytical instrument were used to analyze the sodium content, sulfate group content, chlorine group content, and porosity of the resulting lithium-nickel-manganese-cobalt composite oxide. The Me site occupancy, which indicates the crystallinity of the lithium-nickel-manganese-cobalt composite oxide, was calculated by Rietveld analysis of the diffraction pattern measured using an X-ray diffraction analyzer (XRD). An X-ray diffraction analyzer X'Pert-PRO (manufactured by Spectris Co., Ltd.) was used for the measurement. The Me site occupancy ratio indicates the abundance ratio of metal elements in the metal layer (Me site) of the layered structure of nickel, manganese, cobalt, and additive element M in the lithium-nickel-manganese-cobalt composite oxide. The Me seat occupancy has a correlation with the battery characteristics, and the higher the Me seat occupancy, the better the battery characteristics.

Each condition of Examples and Comparative Examples will be described below.

(Example 1)
In Example 1, 0.9 L of water was added to the reaction tank (5 L) for crystallization in the crystallization step, and the temperature in the tank was set to 40° C. while stirring.

A 25% aqueous sodium hydroxide solution and an appropriate amount of 25% ammonia water, which is an ammonium ion donor, are added to the water in the reaction tank, and the pH of the reaction solution in the tank is measured based on the liquid temperature of 25 ° C. It was adjusted to be 12.8. Also, the ammonium ion concentration of the reaction solution was adjusted to 10 g/L.

Next, nickel sulfate, manganese sulfate, and cobalt chloride were dissolved in water to prepare a 2.0 mol/L raw material solution. In this raw material solution, the element molar ratio of each metal was adjusted to Ni:Mn:Co=1:1:1. Furthermore, sodium hydroxide, which is an alkali metal hydroxide, and sodium carbonate, which is a carbonate, are dissolved in water so that [CO ₃ ²⁻ ]/[OH ⁻ ] is 0.025, and an alkaline solution is prepared. made.

The raw material solution was added to the reaction solution in the reaction tank at 12.9 mL/min, and the ammonium ion donor and the alkaline solution were also added to the reaction solution at a constant rate, so that the ammonium ion concentration in the reaction solution was 10 g/min. The pH was controlled to 12.8 (the pH of the nucleation step) while the pH was maintained at L, and crystallization was performed for 2 minutes and 30 seconds to generate nuclei.

After that, 64% sulfuric acid was added until the pH of the reaction solution reached 11.6 (particle growth process pH) as measured based on a liquid temperature of 25°C. After the pH of the reaction solution reaches 11.6, the supply of the raw material solution, the ammonium ion donor, and the alkaline solution is resumed, and the pH is maintained at 11.6. A transition metal composite hydroxide was obtained by continuing crystallization for 4 hours to grow particles.

As for the reaction atmosphere, first, the inside of the reaction tank was set to an atmospheric atmosphere (oxygen concentration: 21% by volume), and after holding for 32 minutes from the start of crystallization, supply of the raw material solution, aqueous ammonia, and alkaline solution was temporarily stopped. , Nitrogen gas is circulated and replaced at a flow rate of 5 L / min until the oxygen concentration in the space inside the reaction vessel becomes 0.2% by volume or less, and the liquid supply is restarted after the oxygen concentration becomes 0.2% by volume or less. Crystallization was carried out for 3.5 hours.

After solid-liquid separation of the obtained transition metal composite hydroxide by a filter press filtration machine, an ammonium hydrogen carbonate solution having a concentration of 0.05 mol/L was used as a washing liquid, and 1 kg of the transition metal composite hydroxide was Impurities were removed by passing 5 L of the washing liquid through a filter press filtration machine, and then water was further passed through to wash with water. Then, the adhering water of the washed transition metal composite hydroxide was dried to obtain nickel-manganese-cobalt composite hydroxide as a precursor.

(Example 2)
In Example 2, when nickel sulfate, manganese sulfate, and cobalt chloride were dissolved in water to prepare a 2.0 mol/L raw material solution, the molar ratio of nickel, manganese, and cobalt in the raw material solution was Ni:Mn:Co A nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the ratio was adjusted to 6:2:2.

(Example 3)
In Example 3, when nickel sulfate, manganese sulfate, and cobalt chloride were dissolved in water to prepare a 2.0 mol/L raw material solution, the molar ratio of nickel, manganese, and cobalt in the raw material solution was Ni:Mn:Co A nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the ratio was adjusted to 2:7:1.

(Example 4)
In Example 4, nickel-manganese-cobalt composite water was prepared in the same manner as in Example 1, except that [CO ₃ ²⁻ ]/[OH ⁻ ] was adjusted to 0.003 when preparing the alkaline solution. An oxide was obtained.

(Example 5)
In Example 5, nickel-manganese-cobalt composite water was prepared in the same manner as in Example 1, except that [CO ₃ ²⁻ ]/[OH ⁻ ] was adjusted to 0.048 when adjusting the alkaline solution. An oxide was obtained.

(Example 6)
In Example 6, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the pH in the nucleation step was changed to 13.6.

(Example 7)
In Example 7, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the pH in the nucleation step was set to 12.3.

(Example 8)
In Example 8, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the pH in the particle growth step was changed to 11.8.

(Example 9)
In Example 9, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the pH in the particle growth step was changed to 10.6.

(Example 10)
In Example 10, nickel-manganese-cobalt composite hydroxide was prepared in the same manner as in Example 1, except that potassium hydroxide was used as the alkali metal hydroxide and potassium carbonate was used as the carbonate when preparing the alkaline solution. Obtained.

(Example 11)
In Example 11, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that ammonium carbonate was used as the carbonate and the ammonium ion concentration was adjusted to 20 g/L when preparing the alkaline solution. rice field.

(Example 12)
In Example 12, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the temperature in the tank was set to 35°C.

(Example 13)
In Example 13, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that an ammonium hydrogen carbonate solution having a concentration of 1.00 mol/L was used as the cleaning liquid.

(Comparative example 1)
In Comparative Example 1, when nickel sulfate, manganese sulfate, and cobalt chloride were dissolved in water to prepare a 2.0 mol/L raw material solution, the molar ratio of nickel, manganese, and cobalt in the raw material solution was Ni:Mn:Co = 2:6:2, and [CO ₃ ^2- ]/[OH ^- ] was adjusted to 0.001. A composite hydroxide was obtained.

(Comparative example 2)
In Comparative Example 2, nickel-manganese-cobalt composite water was prepared in the same manner as in Example 1 except that only sodium hydroxide was used to prepare the alkaline solution and [CO ₃ ^2- ]/[OH ^- ] was not considered. An oxide was obtained.

(Comparative Example 3)
In Comparative Example 3, nickel-manganese-cobalt composite water was prepared in the same manner as in Example 1, except that [CO ₃ ²⁻ ]/[OH ⁻ ] was adjusted to 0.001 when preparing the alkaline solution. An oxide was obtained.

(Comparative Example 4)
In Comparative Example 4, nickel-manganese-cobalt composite water was prepared in the same manner as in Example 1, except that [CO ₃ ²⁻ ]/[OH ⁻ ] was adjusted to 0.055 when preparing the alkaline solution. An oxide was obtained.

(Comparative Example 5)
In Comparative Example 5, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that the washing step was omitted and the washing with the ammonium hydrogen carbonate solution was not performed.

(Comparative Example 6)
In Comparative Example 6, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that an ammonium hydrogen carbonate solution having a concentration of 0.02 mol/L was used as the cleaning liquid.

(Comparative Example 7)
In Comparative Example 7, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that an ammonium carbonate solution was used as the cleaning liquid.

(Comparative Example 8)
In Comparative Example 8, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that a sodium hydrogen carbonate solution was used as the cleaning liquid.

(Comparative Example 9)
In Comparative Example 9, a nickel-manganese-cobalt composite hydroxide was obtained in the same manner as in Example 1, except that a sodium carbonate solution was used as the cleaning liquid.

Tables 1 and 2 show the above conditions and results.

(Comprehensive evaluation)
As shown in Tables 1 and 2, in Examples 1 to 13, the conditions of the crystallization step and the washing step for the precursor nickel-manganese-cobalt composite hydroxide were all within preferred ranges. Therefore, not only nickel-manganese-cobalt composite hydroxide, but also lithium-nickel-manganese-cobalt composite oxide, which is a positive electrode active material, can be used to remove impurities. , had been sufficiently reduced. Furthermore, in the lithium-nickel-manganese-cobalt composite oxide, the Me site occupancy exceeded 93.0%, resulting in excellent crystallinity and improved battery characteristics.

In particular, regarding the sodium content, both the precursor and the positive electrode active material showed very good results in which all example data were below the lower limit of quantification (analysis) (0.0005% by mass).

Here, the lower limit of quantification means the minimum amount or minimum concentration at which a target component can be analyzed (quantified) by a certain analytical method. Also, the minimum amount (value) at which the signal of the target component can be detected in the measurement is called the detection limit, and the minimum amount (value) at which the reliability of the signal of the target component obtained in the measurement is ensured is called the lower limit of measurement. Furthermore, the lower limit of determination is obtained by multiplying the lower limit of measurement by a dilution factor that indicates how much the original analysis sample has been concentrated or diluted in the process of preparing the sample solution for measurement.

That is, the sodium content in the present invention is determined by acid decomposition of 1 g of the analysis sample to prepare 100 mL of the measurement sample solution (dilution ratio is 100 times) with respect to the lower limit of measurement of 0.05 μg / mL of the atomic absorption spectrometer. , the lower limit of determination is 5 ppm (μg/g), that is, 0.0005% by mass.

On the other hand, in Comparative Examples 1 to 9, the [CO ₃ ²⁻ ]/[OH ⁻ ] in preparing the alkaline solution and the concentration of the ammonium bicarbonate solution used as the cleaning solution were not within the preferable range, and Due to the use of a cleaning liquid other than the ammonium hydrogen solution and the deviation from the optimum conditions, the excellent effects of the examples could not be obtained.

Further, in Examples 1 to 13, in addition to the nickel-manganese-cobalt composite hydroxide, the hollow structure of the lithium-nickel-manganese-cobalt composite oxide also had a porosity in the preferable range of 20 to 50%, and was used as a positive electrode active material. In this case, the contact area between the positive electrode active material and the electrolyte can be made sufficient while maintaining the particle strength within an allowable range without excessively lowering the bulk density, and the battery characteristics are improved.

As described above, nickel-manganese-cobalt composite hydroxide and nickel-manganese-cobalt composite hydroxide are precursors of positive electrode active materials for lithium-ion secondary batteries that can reliably reduce sodium content and improve battery characteristics. It was possible to provide a method for manufacturing a product and a lithium-nickel-manganese-cobalt composite oxide. Furthermore, it is expected to lead to the provision of a lithium ion secondary battery having excellent characteristics.

Although the embodiments and examples of the present invention have been described in detail as described above, it should be understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present invention. , will be easily understood. Accordingly, all such modifications are intended to be included within the scope of the present invention.

For example, a term described at least once in the specification or drawings together with a different, broader or synonymous term can be replaced with the different term anywhere in the specification or drawings. Also, the nickel-manganese-cobalt composite hydroxide, the method for producing the nickel-manganese-cobalt composite hydroxide, and the configuration and operation of the lithium-nickel-manganese-cobalt composite oxide are not limited to those described in the embodiments and examples of the present invention. , various modifications are possible.

S10 crystallization step, S11 nucleation step, S12 particle growth step, S20 washing step

Claims (7)

A nickel-manganese-cobalt composite hydroxide that is a precursor of a positive electrode active material, composed of secondary particles in which primary particles containing nickel, manganese, and cobalt are aggregated, or the primary particles and the secondary particles,
The sodium content contained in the nickel-manganese-cobalt composite hydroxide is less than 0.0005% by mass,
A nickel-manganese-cobalt composite hydroxide, wherein the particles of the nickel-manganese-cobalt composite hydroxide have a porosity of 20 to 50%. 2. The nickel-manganese-cobalt composite hydroxide according to claim 1, wherein the nickel-manganese-cobalt composite hydroxide has a specific surface area of 30 to 40 m ² /g. 3. The nickel-manganese-cobalt composite hydroxide according to claim 1, wherein the nickel-manganese-cobalt composite hydroxide has a sulfate group content of 0.2% by mass or less and a chlorine group content of 0.01% by mass or less. nickel-manganese-cobalt composite hydroxide. 4. The index according to any one of claims 1 to 3, wherein [(d90-d10)/average particle diameter], which is an index showing the breadth of the particle size distribution of the nickel-manganese-cobalt composite hydroxide, is 0.55 or less. The nickel-manganese-cobalt composite hydroxide according to item 1. The nickel-manganese-cobalt composite hydroxide has a general formula: NixMnyCozMt(OH) _2+a (where _x + _y + _z + _t =1, 0.20≤x≤0.80, 0.10≤y≤0. 90, 0.10≦z≦0.50, 0≦t≦0.10, 0≦a≦0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W (at least one of ), the nickel-manganese-cobalt composite hydroxide according to any one of claims 1 to 4. Secondary particles in which primary particles containing lithium, nickel, manganese, and cobalt are aggregated, or a lithium-nickel-manganese-cobalt composite oxide composed of the primary particles and the secondary particles,
The sodium content contained in the lithium-nickel-manganese-cobalt composite oxide is obtained under the following measurement conditions and is less than 0.0005% by mass, and the lithium-nickel-manganese-cobalt composite oxide has a porosity of 20 to 50%. A lithium-nickel-manganese-cobalt composite oxide characterized by:
[Record]
<Conditions for measuring sodium content>
1 g of an analysis sample is acidolyzed to prepare 100 mL of a measurement sample liquid, and the measurement is performed with an atomic absorption spectrometer. The lithium-nickel-manganese-cobalt composite oxide contains a sulfate group content of 0.15% by mass or less, a chlorine group content of 0.005% by mass or less, and a Me site occupancy of 93.0% or more. The lithium-nickel-manganese-cobalt composite oxide according to claim 6.

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