JP2020176049A - Lithium-nickel-manganese-cobalt composite oxide and lithium ion secondary battery - Google Patents

Abstract

To provide a lithium-nickel-manganese-cobalt composite oxide being a cathode active material specifically capable of securely reducing a sodium content, suppressing a sinter aggregation, and further improving battery characteristics by higher porosity and longer life, and also to provide a lithium ion secondary battery.SOLUTION: A nickel-manganese-cobalt composite oxide is a precursor of a cathode active material composed of a secondary particle in which primary particles containing nickel, manganese and cobalt aggregate, or the primary particle and the secondary particle. A sodium content contained in the nickel-manganese-cobalt composite oxide is less than 0.0005 mass%. A porosity of the nickel-manganese-cobalt composite oxide is over 50 to 80% or less. A ratio obtained by dividing an average particle diameter of the lithium-nickel-manganese-cobalt composite oxide by an average particle diameter of a nickel-manganese-cobalt composite hydroxide being a precursor is 0.95-1.05.SELECTED DRAWING: Figure 1

Description

The present invention relates to 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, and a lithium ion secondary battery. .. This application claims priority on the basis of Japanese Patent Application No. 2019-077520 filed on April 16, 2019, which is incorporated by reference to this application.

In recent years, with the spread of portable electronic devices such as smartphones, tablet terminals and notebook computers, it is highly suitable as a battery for hybrid vehicles and electric vehicles, including small and lightweight non-aqueous electrolyte secondary batteries with high energy density. The development needs for output secondary batteries are expanding.

A lithium ion secondary battery can be mentioned as a secondary battery that can meet such needs. The lithium ion secondary battery is composed of an electrolytic solution and the like in addition to the positive electrode and the negative electrode, and the active material of the positive electrode and the negative electrode is a material capable of desorbing or inserting lithium. Lithium-ion secondary batteries are still being actively researched and developed. Among them, lithium-ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode active material have a voltage of 4 V. Since a high-grade voltage can be obtained, it is being put into practical use as a battery having a high energy density.

Among these, lithium nickel-manganese-cobalt composite oxide is attracting attention as a material that has good cycle characteristics of battery capacity and can obtain high output with low resistance. In recent years, power supplies and hybrids for electric vehicles are limited in mounting space. It is also suitable for vehicle power supplies and is regarded as important as in-vehicle power supplies. Generally, the lithium nickel-manganese-cobalt composite oxide is produced by mixing a nickel-manganese-cobalt composite hydroxide as a precursor with a lithium compound and firing the mixture.

This nickel-manganese-cobalt composite hydroxide contains impurities such as sulfate roots, chlorine roots, and sodium derived from raw materials and chemicals used in the manufacturing process. These impurities are a layered structure of lithium nickel manganese cobalt in order to induce side reactions and worsen the reaction with lithium in the step of mixing the nickel manganese cobalt composite hydroxide and the lithium compound and firing them. It reduces the crystallinity of the composite oxide.

The lithium nickel-manganese-cobalt composite oxide having low 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, and the battery capacity decreases. Further, since these impurities hardly contribute to the charge / discharge reaction, in the battery configuration, the negative electrode material has to be used in excess for the amount corresponding to the irreversible capacity of the positive electrode material. As a result, the capacity per weight or volume of the battery as a whole becomes small, and excess lithium is accumulated in the negative electrode as an irreversible capacity, which poses a problem from the viewpoint of safety.

Furthermore, sodium, potassium, calcium, magnesium, etc. are dissolved in lithium sites, so that the particles of the lithium nickel manganese cobalt composite oxide are easily sintered and aggregated, and the lithium ion secondary produced using this is easily sintered and aggregated. The reactivity of the battery deteriorates, and the output characteristics and the battery capacity decrease.

Examples of impurities include sulfate roots, chlorine roots, sodium and the like, and techniques for removing these impurities have been disclosed so far.

For example, in Patent Document 1, a crystallization step for obtaining a niobium-containing transition metal composite hydroxide is performed, and the obtained niobium-containing transition metal composite hydroxide is used as an aqueous carbonate solution such as potassium carbonate, sodium carbonate, or ammonium carbonate. It is disclosed that the sulfate roots and chlorine roots 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, an alkali solution used for pH adjustment is used as a mixed solution of an alkali metal hydroxide and a carbonate, thereby providing impurities. It is disclosed to reduce sulfate roots, chlorine roots, and carbonate roots.

Further, in Patent Documents 3 to 4, nickel manganese composite hydroxide particles or nickel composite hydroxide particles having a void structure inside the particles obtained in the crystallization step are referred to as potassium carbonate, sodium carbonate, potassium hydrogen carbonate and the like. It is disclosed that sulfate roots, chlorine roots, and sodium can be reduced by washing with an aqueous carbonate solution such as sodium hydrogen carbonate.

Further, in Patent Document 5, a nickel-cobalt-M element-containing aqueous solution or an aqueous dispersion obtained by mixing a nickel ammine complex, a cobalt ammine complex and an M element source is heated to obtain a nickel ammine complex and a cobalt ammine complex. It is disclosed to use a nickel-cobalt-M element-containing composite compound which is thermally decomposed and has a low content of impurities such as sulfate root, chlorine root, sodium and iron.

JP-A-2015-122269 Japanese Unexamined Patent Publication No. 2016-117625 International Publication No. 2015/146598 Japanese Unexamined Patent Publication No. 2015-191848 International Publication No. 2012/020768

However, Patent Documents 1 and 2 do not mention the removal of sodium at all. Further, regarding Patent Documents 3 to 4, even in a solid level precursor having a porosity of about 3%, 0.001 to 0.015% by mass of sodium still remains, and sodium reduction is insufficient. is there. Further, with respect to Patent Document 5, since a nickel-cobalt-M element-containing composite compound is obtained by thermal decomposition, a sufficient battery can be used as a positive electrode active material from the viewpoints of particle sphere, particle size distribution, and specific surface area. It is questioned whether it will be a characteristic. In addition to removing impurities, it is expected that the battery characteristics will be further improved, such as increasing the porosity and extending the life of the particles, and suppressing sintering and agglomeration.

Therefore, an object of the present invention is to surely reduce the content of sodium among impurities that hardly contribute to the charge / discharge reaction, suppress sintering and aggregation, and further increase the void ratio and the life of the battery. An object of the present invention is to provide a lithium nickel manganese cobalt composite oxide and a lithium ion secondary battery, which are positive electrode active materials capable of improving their characteristics.

The lithium nickel manganese cobalt composite oxide according to one aspect of the present invention is a secondary particle in which primary particles containing lithium, nickel, manganese, and cobalt are aggregated, or a lithium nickel manganese composed of the primary particle and the secondary particle. It is a cobalt composite oxide, and the sodium content in the lithium nickel manganese cobalt composite oxide is less than 0.0005% by mass, and the void ratio of the particles of the lithium nickel manganese cobalt composite oxide is more than 50 to 80. %, And the ratio obtained by dividing the average particle size of the lithium nickel manganese cobalt composite oxide by the average particle size of the precursor nickel manganese cobalt composite hydroxide is 0.95 to 1.05. It is a feature.

By doing so, a lithium ion secondary battery capable of reliably reducing the sodium content, suppressing sintering and agglomeration, increasing the porosity and extending the life, and having high filling property and high capacity. Lithium nickel-manganese-cobalt composite oxide, which is the positive electrode active material of the above, can be provided.

At this time, in one aspect of the present invention, when 100 or more randomly selected particles of the lithium nickel manganese cobalt composite oxide are observed with a scanning electron microscope, aggregation of secondary particles is observed. The number may be 5% or less of the total number of observed secondary particles.

By doing so, it is possible to provide a lithium nickel manganese cobalt composite oxide which is a positive electrode active material of a lithium ion secondary battery capable of suppressing sintering aggregation, having high filling property, and increasing the capacity.

At this time, in one aspect of the present invention, the sulfate root content contained in the lithium nickel-manganese cobalt composite oxide is 0.15% by mass or less, the chlorine root content is 0.005% by mass or less, and the Me seat occupancy rate. May be 93.0% or more.

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

At this time, in one aspect of the present invention, the content of at least one or more of potassium, calcium, and magnesium contained in the lithium nickel manganese cobalt composite oxide may be less than 0.0005% by mass.

By doing so, it is possible to provide a lithium nickel manganese cobalt composite oxide which is a positive electrode active material of a lithium ion secondary battery capable of further reducing the content of impurities and increasing the capacity.

At this time, in another aspect of the present invention, the lithium ion secondary battery may include at least a positive electrode containing the lithium nickel manganese cobalt composite oxide.

In this way, the positive electrode activity of the lithium nickel-manganese-cobalt composite oxide capable of reliably reducing the sodium content, suppressing sintering aggregation, increasing the void ratio, high filling property, and high capacity can be achieved. A lithium ion secondary battery provided with a positive electrode containing a substance can be provided.

According to the present invention, lithium is a positive electrode active material that can surely reduce the sodium content, suppress sintering and aggregation, and further improve battery characteristics by increasing the void ratio and extending the life. Nickel manganese cobalt composite oxide and lithium ion secondary batteries can be provided.

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

As a result of diligent studies to solve the above problems, the present inventor controlled the reaction atmosphere in the crystallization step in the production of nickel-manganese-cobalt composite hydroxide, and used the alkaline solution used in the crystallization step as alkali metal bicarbonate. In addition to preparing a mixed solution of the product and carbonate, the transition metal composite hydroxide obtained in the crystallization step is used as a washing solution containing hydrogen carbonate (bicarbonate) in the washing step, which is an ammonium hydrogen carbonate solution. The present invention has been completed based on the finding that impurities such as sulfate roots, chlorine roots and sodium can be reduced more efficiently and to a lower concentration by washing with. Further, as described above, by using the nickel-manganese-cobalt composite hydroxide whose sodium content is surely reduced as a precursor, sintering aggregation is suppressed, the filling property is high, and the capacity is increased. The present invention has been completed based on the finding that a lithium nickel-manganese-cobalt composite oxide, which is a possible positive electrode active material for a lithium ion secondary battery, can be obtained. Hereinafter, preferred embodiments of the present invention will be described.

The present embodiment described below does not unreasonably limit the content of the present invention described in the claims, and can be modified without departing from the gist of the present invention. Moreover, not all of the configurations described in the present embodiment are indispensable as the means for solving the present invention. A method for producing a nickel-manganese-cobalt composite hydroxide, a nickel-manganese-cobalt composite hydroxide, a lithium-nickel-manganest-cobalt composite oxide, and a lithium ion secondary battery according to an embodiment of the present invention will be described in the following order.
1. 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 process 3-1-2. Particle growth process 3-2. Cleaning process 4. Lithium ion secondary battery

<1. Nickel Manganese Cobalt Composite Hydroxide ＞
The nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention is a secondary particle in which primary particles containing nickel, manganese, and cobalt are aggregated, or a positive electrode active material composed of the primary particles and the secondary particles. Is a precursor of.

The sodium content of the nickel-manganese-cobalt composite hydroxide is less than 0.0005% by mass, and the void ratio of the particles of the nickel-manganese-cobalt composite hydroxide is more than 50 to 80% (that is, 50). It is characterized in that it is larger than% and 80% or less). Hereinafter, the nickel-manganese-cobalt composite hydroxide according to the embodiment of the present invention will be specifically described.

[Particle composition]
Nickel manganese cobalt composite hydroxide, the composition has the general _{formula: Ni x Mn y 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, It is preferable to adjust so as to be represented by 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 ≦ 0.6 is more preferable for x indicating the nickel content in consideration of electrical characteristics and thermal stability.

Further, y indicating the manganese content is preferably 0.10 ≦ y ≦ 0.90. When manganese is added in this range, the durability characteristics 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, the effect of improving the durability characteristics and safety of the battery cannot be sufficiently obtained, while when it exceeds 0.9, the metal elements contributing to the Redox reaction decrease and the battery capacity. Is not preferable because it may decrease.

Further, in the above general formula, z indicating the cobalt content is preferably 0.10 ≦ z ≦ 0.50. By adding cobalt appropriately, the expansion and contraction behavior of the crystal lattice due to the improvement of cycle characteristics and the desorption and insertion of Li due to charge and discharge can be reduced, but when z is less than 0.10, the expansion and contraction behavior of the crystal lattice. It is not preferable because it is difficult to obtain a sufficient reduction effect of. On the other hand, if the amount of cobalt added is too large and z exceeds 0.5, the initial discharge capacity may be significantly reduced, which is not preferable because there is a problem that it is disadvantageous in terms of cost.

The additive element M is one or more of Mg, Ca, Al, 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 a thing. The t indicating the content of the additive element M is preferably 0 ≦ t ≦ 0.10. If t exceeds 0.1, the amount of metal elements contributing to the Redox reaction may decrease, which is not preferable because the battery capacity may decrease.

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

[Particle structure]
The nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention is composed of secondary particles in which a plurality of primary particles are aggregated, or both primary particles and secondary particles thereof. As the shape of the primary particles constituting the secondary particles, various shapes such as a plate shape, a needle shape, a rectangular parallelepiped shape, an elliptical shape, and a rhombohedral shape can be adopted. Further, the agglutination state of a plurality of primary particles can be applied to the present invention not only in the case of agglutination in a random direction but also in the case of agglutination of particles in the major axis direction radially from the center.

As the agglomerated state, it is preferable that the plate-shaped or needle-shaped primary particles are aggregated in a random direction to form the secondary particles. In the case of such a structure, almost uniform voids are generated between the primary particles, and when the lithium compound is mixed and fired, the molten lithium compound spreads in the secondary particles and the lithium is sufficiently diffused. Because it is done.

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

[Particle internal structure]
The nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention has a porous structure inside secondary particles. When a lithium metal composite oxide having this porous structure and using a nickel manganese cobalt composite hydroxide as a precursor is used as a positive electrode active material, the contact area with the electrolytic solution increases, so that lithium ions are formed. The secondary battery has excellent output characteristics. Further, unlike the hollow structure, the filling property when used as a positive electrode active material can be maintained.

By the way, "having a porous structure inside a secondary particle" means a structure in which voids in the secondary particle are dispersed over the entire particle. As shown in FIG. 1, this porous structure can be confirmed by observing the cross section of the nickel-manganese-cobalt composite hydroxide and the lithium metal composite oxide with a scanning electron microscope as shown in the cross-sectional SEM image. ..

Further, the nickel-manganese-cobalt composite hydroxide having a porous structure preferably has a porosity of 10 to 90% measured in cross-sectional observation of the particles, and more than 50 to 80% (that is, more than 50%). It is more preferably 80% or less). Further, the lithium metal composite oxide having a porous structure also preferably has a porosity of 10 to 90% as measured in cross-sectional observation of the particles, and further, more than 50 to 80% (that is, larger than 50% and 80). % Or less) is more preferable. As a result, the bulk density of the obtained positive electrode active material is not excessively lowered, the particle strength is kept within an allowable range, the life of the positive electrode active material is extended, and the contact area between the positive electrode active material and the electrolytic solution is sufficiently increased. It is possible to further improve the battery characteristics.

In the present invention, the nickel-manganese-cobalt composite hydroxide and the lithium metal composite oxide have a porous structure. For example, for a metal composite hydroxide that is a source of transition metals such as nickel, manganese, and cobalt during mixing and firing, by adjusting the crystallization conditions during the manufacturing process, a solid structure or hollow It is also possible to mix structural and porous structures, respectively, in combination and ratio, and the obtained metal composite oxide is compared with a simple mixture of solid, hollow, and porous products. Therefore, there is an advantage that the overall composition and particle size can be stabilized.

[Average particle size (MV)]
The nickel-manganese-cobalt composite hydroxide preferably has 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, when the average particle size exceeds 20 μm, the specific surface area of the positive electrode active material decreases, and the interface with the electrolytic solution of the battery decreases, so that the resistance of the positive electrode increases and the output characteristics of the battery may deteriorate. It is not preferable because it exists. Therefore, in the nickel-manganese-cobalt composite hydroxide, if the average particle size of the particles is adjusted to be 3 to 20 μm, preferably 3 to 15 μm, and more preferably 4 to 12 μm, this positive electrode active material can be used as the 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.

The method for measuring the average particle size is not particularly limited, but can be obtained from, for example, a volume reference distribution measured by using a laser diffraction / scattering method.

[Impurity content]
Generally, nickel-manganese-cobalt composite hydroxide contains sulfate root, chlorine root, sodium, potassium, calcium, magnesium and the like 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 to reduce the content thereof. Conventionally, techniques for removing these impurities have been disclosed, but these techniques are still insufficient.

Therefore, the sodium content in the nickel-manganese-cobalt composite hydroxide according to the embodiment of the present invention is less than 0.0005% by mass. By doing so, it is possible to provide a nickel manganese cobalt composite hydroxide which is a precursor of a positive electrode active material of a lithium ion secondary battery capable of reliably reducing the sodium content and improving the battery characteristics. it can.

As described above, in the prior art, 0.001 to 0.015 of sodium remains in a mass%, which is insufficient for reducing sodium. Further, although there is a document in the prior art that describes that the sodium content is a certain value or less, the nickel-manganese-cobalt composite hydroxide according to the embodiment of the present invention and the lithium nickel-manganese-cobalt composite oxide described later As described above, composite hydroxides and composite oxides having an extremely low sodium content of less than 0.0005% by mass are not actually disclosed. By the production method described later, an extremely low concentration of sodium content of less than 0.0005% by mass can be achieved. By doing so, it is possible to suppress sintering and aggregation when the lithium nickel manganese cobalt composite oxide is formed.

Further, it is preferable that the sulfate root content contained in the nickel-manganese-cobalt composite hydroxide is 0.2% by mass or less and the chlorine root content is 0.01% by mass or less. In this way, nickel-manganese-cobalt composite hydroxylation, which is a precursor of the positive electrode active material of the lithium ion secondary battery, which can surely reduce the contents of sulfate root, chlorine root and sodium and improve the battery characteristics. Can provide things.

The content of at least one or more of potassium, calcium, and magnesium contained in the nickel-manganese-cobalt composite hydroxide is preferably less than 0.0005% by mass. In this way, a precursor of a positive electrode active material capable of obtaining a lithium ion secondary battery capable of further reducing the content of impurities and further improving the battery characteristics by increasing the void ratio and extending the life. A nickel-manganese-cobalt composite hydroxide can be provided.

The content of each impurity can be determined, for example, by using the analysis method shown below. In addition to sodium, potassium, calcium, magnesium and the like can be obtained by acid decomposition-atomic absorption spectrometry, acid decomposition-ICP emission spectroscopy and the like. For sulfate roots, the total sulfur content of nickel-manganese-cobalt composite hydroxide is analyzed by combustion infrared absorption method, acid decomposition-ICP emission spectroscopic analysis, etc., and the total sulfur content is determined by sulfate root (SO). It can be obtained by converting to ₄ ^2- ). Chlorine roots can be obtained by separating the chlorine roots contained in nickel-manganese-cobalt composite hydroxide directly or by distillation in the form of silver chloride or the like and analyzing them by a fluorescent X-ray (XRF) analysis method. You can.

[Particle size distribution]
The nickel-manganese-cobalt composite hydroxide is preferably adjusted so that [(d90-d10) / average particle size], 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 the index [(d90-d10) / average particle size] indicating 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 having a very large particle size (large diameter particles) with respect to the average particle size are likely to exist.

Such characteristics of the particle size distribution at the precursor stage have a great influence on the positive electrode active material obtained after the firing step. 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 a local reaction of the fine particles, which may reduce safety and also have a large specific surface area. Is not preferable because the cycle characteristics may be deteriorated because the particles are selectively deteriorated. On the other hand, when the positive electrode is formed by using the positive electrode active material in which many large-diameter particles are present, the reaction area between the electrolytic solution and the positive electrode active material cannot be sufficiently obtained, and the battery output decreases due to the increase in reaction resistance. It is not preferable because it may occur.

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 and fine particles when used as a positive electrode active material Since the proportion of large-diameter particles is reduced, a lithium ion secondary battery using this positive electrode active material as the positive electrode is more safe 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, when the number of particles in each particle size is accumulated from the smallest particle size, the cumulative volume is the total volume of all particles. It means a particle size of 10%. On the other hand, d90 means a particle size in which the cumulative volume is 90% of the total volume of all particles when the number of particles in each particle size is accumulated from the smallest particle size. The method for obtaining the average particle size and d90 and d10 is not particularly limited, but can be obtained from, for example, a volume reference distribution measured by using a laser diffraction / scattering method.

[Specific surface area]
The nickel-manganese-cobalt composite hydroxide is preferably adjusted so that the specific surface area is 10 to 80 m ² / g. This is because if the specific surface area is within the above range, a sufficient surface area of particles that can come into contact with the molten lithium compound can be secured when the particles are mixed with the lithium compound and fired, and the particle strength when the positive electrode active material is obtained is also satisfactory. ..

On the other hand, if the specific surface area is less than 10 m ² / g, the contact with the molten lithium compound becomes insufficient when the lithium compound is mixed and fired, and the crystallinity of the obtained lithium nickel manganese cobalt composite oxide is lowered. However, when a lithium ion secondary battery is configured as a positive electrode material, there is a concern that the diffusion of lithium in the solid phase may be hindered and the battery capacity may decrease. Further, when the specific surface area exceeds 80 m ² / g, when the mixture is mixed with a lithium compound and fired, crystal growth proceeds too much, and cation mixing in which nickel is mixed in the lithium layer of the lithium transition metal composite oxide which is a layered compound. Is not preferable because the charge / discharge capacity may decrease.

Further, in the case of a porous structure in which the voids in the secondary particles are dispersed throughout the particles, which is obtained in the present invention, the adjustment is made so as to be 50 to 60 m ² / g. preferable. If the specific surface area is less than 50 m ² / g, it is difficult to obtain a predetermined porosity, and it is not possible to sufficiently secure the reaction area with the lithium compound at the time of firing. If the specific surface area exceeds 60 m ² / g, the filling property may deteriorate when the positive electrode active material has a porous structure. Further, when the specific surface area is within the above range, a sufficient surface area of particles that can come into contact with the molten lithium compound can be sufficiently secured when the particles are mixed with the lithium compound and fired, and the particle strength when the positive electrode active material is obtained can be further satisfied. Because.

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

FIG. 1 shows a cross-sectional SEM photograph of a nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention. As described above, the nickel-manganese-cobalt composite hydroxide according to the embodiment of the present invention has a porous internal structure as shown in FIG.

According to the nickel-manganese-cobalt composite hydroxide according to the embodiment of the present invention, the lithium ion capable of reliably reducing the sodium content and further improving the battery characteristics by increasing the void ratio and extending the life. A precursor of a positive electrode active material of a secondary battery can be provided. Further, as described above, by using the nickel-manganese-cobalt composite hydroxide in which the sodium content is surely reduced as a precursor, sintering aggregation is suppressed, the filling property is high, and the capacity is increased. A lithium nickel manganese cobalt composite oxide, which is a possible positive electrode active material for a lithium ion secondary battery, can be obtained.

<2. Lithium Nickel Manganese Cobalt Composite Oxide ＞
The lithium nickel manganese cobalt composite oxide according to the 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 of the lithium nickel-manganese cobalt composite oxide is less than 0.0005% by mass, and the void ratio of the particles of the lithium nickel manganese cobalt composite oxide is more than 50 to 80% (that is, more than 50%). It is characterized by being largely 80% or less).

Further, the sulfate root content contained in the lithium nickel manganese cobalt composite oxide is 0.15% by mass or less, the chlorine root content is 0.005% by mass or less, and the Me seat occupancy rate is 93.0% or more. It is preferable to have.

The ratio obtained by dividing the average particle size of the lithium nickel manganese cobalt composite oxide by the average particle size of the precursor nickel manganese cobalt composite hydroxide, that is, "MV / nickel manganese cobalt of the lithium nickel manganese cobalt composite oxide". The "MV of the composite hydroxide" (hereinafter, also referred to as "MV ratio") can be evaluated as an index showing sintering aggregation. The range of the MV ratio is 0.95 to 1.05, preferably 0.97 to 1.03.

When this MV ratio is in the above range, the positive electrode active material is composed of a lithium nickel-manganese-cobalt composite oxide in which agglomeration of secondary particles hardly occurs due to sintering agglomeration. Become. A secondary battery using such a positive electrode active material has high filling property, high capacity, and excellent uniformity with little variation in characteristics.

On the other hand, when the MV ratio exceeds 1.05, the specific surface area and the filling property may decrease due to sintering and aggregation. A secondary battery using such a positive electrode active material may deteriorate in output characteristics and battery capacity due to deterioration in reactivity. In addition, when charging and discharging are repeated, there is a risk that the positive electrode will selectively collapse from the weakly-strength part where the secondary particles are agglomerated, and the cycle characteristics will be significantly impaired. For example, it is 1.05 or less, and preferably 1.03 or less.

Further, when the MV ratio is less than 0.95, it is considered that a part of the primary particles is missing from the secondary particles in the manufacturing process of the lithium nickel manganese cobalt composite oxide, and the particle size is reduced. As a result, the particle size distribution may become wider, so it is 0.95 or more, preferably 0.97 or more.

The MV of the nickel manganese cobalt composite hydroxide means the MV of the nickel manganese cobalt composite hydroxide used as a precursor in producing the lithium nickel manganese cobalt composite oxide. Further, the MV of the lithium nickel manganese cobalt composite oxide means the MV of the lithium nickel manganese cobalt composite oxide after the crushing step when the crushing step is performed. The MV of each particle can be measured by a laser diffraction / scattering type particle size analysis and measurement device, and the number of particles at each particle size is accumulated from the side with the smaller particle size, and the cumulative volume is the total volume of all particles. It means the particle size which is the average value of the total volume.

In addition, when 100 or more randomly selected particles of lithium nickel manganese cobalt composite oxide were observed by a scanning electron microscope (SEM), the number of particles in which agglomeration of secondary particles was observed was the total number observed. It may be 5% or less, 3% or less, or 2% or less with respect to the number of secondary particles. When the number of observed agglutination of secondary particles is in the above range, it indicates that the sintering agglutination of secondary particles is sufficiently suppressed. Further, when the MV of the positive electrode active material is in the above range, the number of observed aggregation of secondary particles can be easily set in the above range. The magnification when observing with a scanning electron microscope (SEM) is, for example, about 1000 times.

When the number of observed secondary particle aggregation is 5% or less of the total number of observed secondary particles, the positive electrode active material almost causes aggregation of secondary particles due to sintering aggregation. It is composed of lithium nickel manganese cobalt composite oxide which is not used. A secondary battery using such a positive electrode active material has high filling property, high capacity, and excellent uniformity with little variation in characteristics.

On the other hand, when the number of observed secondary particle aggregation exceeds 5% of the total number of observed secondary particles, the specific surface area and filling property may decrease due to sintering aggregation. A secondary battery using such a positive electrode active material may deteriorate in output characteristics and battery capacity due to deterioration in reactivity. In addition, when charging and discharging are repeated, there is a risk that the positive electrode will selectively collapse from the weakly-strength part where the secondary particles are agglomerated, and the cycle characteristics will be significantly impaired. For example, it is preferably 5% or less.

The content of at least one or more of potassium, calcium, and magnesium contained in the lithium nickel-manganese-cobalt composite oxide is preferably less than 0.0005% by mass. By doing so, it is possible to provide a lithium nickel manganese cobalt composite oxide which is a positive electrode active material of a lithium ion secondary battery capable of further reducing the content of impurities and increasing the capacity.

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 lithium nickel-manganese-cobalt composite oxide can be used as a raw material for a positive electrode active material for a lithium ion secondary battery.

Lithium-nickel-manganese-cobalt composite oxide used as the positive electrode active material includes the precursor nickel-manganese-cobalt composite hydroxide, lithium carbonate (Li ₂ CO ₃ : melting point 723 ° C.), and lithium hydroxide (LiOH: melting point 462). After mixing with lithium compounds such as lithium nitrate (LiNO ₃ : melting point 261 ° C.), lithium chloride (LiCl: melting point 613 ° C.), lithium sulfate (Li ₂ SO ₄ : melting point 859 ° C.), the firing step is performed. Obtained by passing.

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 firing step, carbonate roots, hydroxyl groups, nitrate roots, chlorine roots, and sulfate roots, which are also constituents of the lithium compound, volatilize, but only a small part remains in the positive electrode active material. In addition to the particle size distribution and specific surface area, including non-volatile components such as sodium, the porous structure of secondary particles will almost inherit the characteristics of the precursor nickel-manganese-cobalt composite hydroxide.

According to the lithium nickel-manganese-cobalt composite oxide according to the embodiment of the present invention, the lithium ion capable of reliably reducing the sodium content and further improving the battery characteristics by increasing the void ratio and extending the life. A positive electrode active material for a secondary battery can be provided.

<3. Manufacturing method of nickel-manganese-cobalt composite hydroxide>
Next, a method for producing a nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention will be described with reference to FIG. The method for producing a nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention comprises 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, a 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 feeder, and an alkaline solution. To 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 is a molar ratio of the carbonate to the alkali metal hydroxide in the mixed solution [CO _3]. ^2- ] / [OH ⁻ ] is 0.002 to 0.050, and in the crystallization step S10, crystallization is performed by switching the atmosphere a plurality of times in two stages of an oxidizing atmosphere and a non-oxidizing atmosphere. The cleaning solution in the cleaning step S20 is characterized by being an ammonium hydrogen carbonate solution having a concentration of 0.05 mol / L or more. Hereinafter, each step will be described in detail.

<3-1. Crystallization process>
In the crystallization step S10, a 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 feeder, and an alkaline solution. To get.

Further, the crystallization step S10 preferably further includes a nucleation step S11 and a particle growth step S12. In the nucleation step S11, an alkaline solution is added and nucleation is performed in the reaction solution so that the pH measured based on the liquid temperature of 25 ° C. is 12.0 to 14.0. In the particle growth step S12, nucleation is performed. It is preferable to add an alkaline solution to the reaction solution containing nuclei formed in step S11 so that the pH measured with reference to the liquid temperature of 25 ° C. is 10.5-12.0. Details will be described later.

In the conventional continuous crystallization method, the nucleation reaction and the nucleation reaction proceed simultaneously in the same reaction vessel, so that 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 in the present invention, the time when the nucleation reaction mainly occurs (nucleation step) and the time when the particle growth reaction mainly occurs (particle growth step) are clarified. By separating, a transition metal composite hydroxide having a narrow particle size distribution can be obtained even if both steps are performed in the same reaction vessel. Further, by making the alkaline solution a mixed solution of alkali metal hydroxide and carbonate, impurities such as sulfate roots can be reduced.

The materials and conditions used in the method for producing a nickel-manganese-cobalt composite hydroxide in the present invention will be described in detail below.

[Raw material solution containing nickel, manganese and cobalt]
The metal salt such as nickel salt, manganese salt, and cobalt salt used in the raw material solution containing nickel, manganese, and cobalt is not particularly limited as long as it is a water-soluble compound, but is sulfate, nitrate, and chloride. You can use things. For example, nickel sulfate, manganese sulfate, and cobalt sulfate are preferably used.

Further, if necessary, a compound containing one or more kinds of 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 at least one of Al, Ti, V, Cr, Zr, Nb, Mo, and W, and titanium sulfate, ammonium peroxotitanium, and titanium oxalate are used. Potassium, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, zirconium nitrate, niobium oxalate, ammonium molybdate, sodium tungstate, ammonium tungstate and the like can be used.

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

The concentration of the raw material solution is preferably 1.0 to 2.6 mol / L in total of the metal salts, and more preferably 1.0 to 2.2 mol / L. If it is less than 1.0 mol / L, the concentration of the obtained hydroxide slurry is low and the productivity is inferior. 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 piping of the equipment, and the piping must be kept warm or heated, which is costly.

Further, the amount of the raw material solution supplied to the reaction vessel is preferably such that the concentration of the crystallized product at the time when the crystallization reaction is completed is approximately 30 to 250 g / L, more preferably 80 to 150 g / L. .. If the concentration of the crystallized product is less than 30 g / L, the aggregation of the primary particles may be insufficient, and if it exceeds 250 g / L, the raw material solution to be added is sufficiently diffused in the reaction vessel. However, the particle growth may be biased.

[Ammonium ion feeder]
The ammonium ion feeder in the reaction solution is not particularly limited as long as it is a water-soluble compound, and aqueous ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used, for example, aqueous ammonia. It is preferable to use ammonium sulfate.

The ammonium ion concentration in the reaction solution is preferably adjusted to 3 to 25 g / L, more preferably 5 to 20 g / L, and even 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, increase the solubility of the metal ions, promote the growth of primary particles, and dense nickel-manganese-cobalt composite hydroxide. Particles are easy to obtain. Furthermore, since the solubility of metal ions is stable, nickel-manganese-cobalt composite hydroxide particles having a uniform shape and particle size can be easily obtained. By setting the ammonium ion concentration in the reaction solution to 3 to 25 g / L, it is easy to obtain composite hydroxide particles having a finer shape and a uniform 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, primary particles with a uniform shape and particle size are not formed, and gel-like nuclei are formed. The particle size distribution may become wider. On the other hand, when the ammonium ion concentration exceeds 25 g / L, the solubility of the metal ion becomes too large, and the amount of the metal ion remaining in the reaction solution increases, which may cause a deviation in the composition. The concentration of ammonium ions can be measured by the 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 [CO ₃ ^2- ] / [OH ⁻ ], which represents the molar ratio of alkali metal hydroxide to carbonate, of 0.002 to 0.050. Further, it is more preferably 0.005 to 0.030, and further preferably 0.010 to 0.025.

By making the alkaline solution a mixed solution of alkali metal hydroxide and carbonate, anions such as sulfate roots and chlorine roots remaining as impurities are added to the nickel manganese cobalt composite hydroxide obtained in the crystallization step S10. , Carbonate root can be replaced and removed. Compared to sulfate roots and chlorine roots, carbonated roots are more likely to volatilize when heated, and are preferentially volatilized in the process of mixing nickel-manganese-cobalt composite hydroxide and lithium compound and firing. It hardly remains in the lithium nickel manganese cobalt composite oxide which is a positive electrode material.

If [CO ₃ ^2- ] / [OH ⁻ ] is less than 0.002, the substitution of sulfate roots and chlorine roots, which are impurities derived from the raw materials, with carbonate ions becomes insufficient in the crystallization step S10, and these Impurities can be easily incorporated into the nickel-manganese-cobalt composite hydroxide. On the other hand, even if [CO ₃ ^2- ] / [OH ⁻ ] exceeds 0.050, the reduction of sulfate roots and chlorine roots, which are impurities derived from raw materials, does not change, and excessive carbonate addition increases the cost. Let me.

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 of addition can be easily controlled.

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 of addition can be easily controlled.

The method of adding the alkaline solution to the reaction vessel is not particularly limited, and the solution is added so that the pH of the reaction solution is maintained in the range described later with a pump capable of controlling the flow rate, such as a metering pump. do it.

[PH control]
In the crystallization step S10, a nucleation step S11 in which an alkaline solution is added to perform nucleation so that the pH of the reaction solution measured based on the liquid temperature of 25 ° C. becomes 12.0 to 14.0, and this nucleation step S11. 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 10.5-12.0, and the nuclei are formed. It is more preferable to include the particle growth step S12 to be grown.

That is, the nucleation reaction and the particle growth reaction do not proceed at the same time in the same tank, but mainly the time during which the nucleation reaction (nucleation step S11) occurs and the particle growth reaction (particle growth step S12). It is characterized by a clear separation from the time when The nucleation step S11 and the particle growth step S12 will be described in detail below.

<3-1-1. Nucleation process>
In the nucleation step S11, it is preferable to control the pH of the reaction solution so as to be in the range of 12.0 to 14.0 based on the liquid temperature of 25 ° C. If the pH exceeds 14.0, the nuclei produced may become too fine and the reaction solution may gel. On the other hand, if the pH is less than 12.0, the nucleation and the growth reaction of the nuclei occur, so that the range of the particle size distribution of the nuclei formed becomes wide and may become inhomogeneous.

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 almost 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 based on the liquid temperature of 25 ° C., and more preferably 11.0 to 12.0. When the pH exceeds 12.0, the number of newly generated nuclei increases and fine secondary particles are generated, so that a hydroxide having a good particle size distribution may not be obtained. On the other hand, when the pH is less than 10.5, the solubility of ammonium ions is high, and the amount of metal ions remaining in the liquid without precipitation increases, so that the production efficiency may deteriorate.

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 produced in the nucleation step S11 is preferentially caused, and new nucleation is formed. The resulting nickel-manganese-cobalt composite hydroxide can be homogeneous and have a narrower particle size distribution range.

When the pH is 12.0, it is a boundary condition between nucleation and nuclear growth. Therefore, depending on the presence or absence of nuclei present in the reaction solution, either the nucleation step or the particle growth step should be used. Can be done. That is, if the pH of 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. The above-mentioned hydroxide having a narrower particle size distribution and a relatively large particle size can be 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, since there are no nuclei to grow, nucleation occurs preferentially, and the particle growth step By lowering the pH of S12 below 12.0, the nuclei produced grow and better hydroxides are obtained.

In any case, the pH of the particle growth step S12 may be controlled to a value lower than the pH of the nucleation step S11, and in order to clearly separate nucleation and particle growth, the pH of the particle growth step S12 should be adjusted. , The pH of the nucleation step S11 is preferably 0.5 or more, and more preferably 1.0 or more.

As described above, by clearly separating the nucleation step S11 and the particle growth step S12 by pH, nucleation occurs preferentially in the nucleation step S11, nucleation hardly occurs, and conversely, particle growth occurs. In step S12, only nucleation occurs and almost no new nuclei are produced. As a result, in the nucleation step S11, a homogeneous nucleus having a narrow particle size distribution range can be formed, and in the particle growth step S12, the nucleus can be uniformly grown. Therefore, in the method for producing a nickel-manganese-cobalt composite hydroxide, it is possible to obtain uniform nickel-manganese-cobalt composite hydroxide particles having a narrower particle size distribution range.

[Reaction solution temperature]
In the reaction vessel, the temperature of the reaction solution is preferably set to 20 to 80 ° C, more preferably 30 to 70 ° C, and even more preferably 35 to 60 ° C. When the temperature of the reaction solution is less than 20 ° C., the solubility of metal ions is low, so that nucleation is likely to occur and control becomes difficult. On the other hand, if the temperature exceeds 80 ° C., the volatilization of ammonia is promoted, so that an excess ammonium ion feeder 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-manganese-cobalt 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 an embodiment of the present invention, crystallization is performed by switching the atmosphere a plurality of times in two stages of an oxidizing atmosphere and a non-oxidizing atmosphere. Specifically, crystallization is performed in an oxidizing atmosphere, then the atmosphere in the reaction vessel is switched to a non-oxidizing atmosphere for crystallization, and then the oxidizing atmosphere and the non-oxidizing atmosphere are appropriately switched a plurality of times to crystallize. Perform analysis.

When the atmosphere in the reaction vessel in the crystallization step S10 is controlled to a non-oxidizing atmosphere, the growth of the primary particles forming the nickel-manganese-cobalt composite hydroxide is promoted, the primary particles are large and dense, and the particle size is large. Moderately large secondary particles are formed. On the other hand, when the atmosphere in the reaction vessel during the crystallization step is controlled to an oxidizing atmosphere, the growth of the primary particles forming the nickel-manganese-cobalt composite hydroxide is suppressed, and the particles are composed of fine primary particles, and the space is located in the center of the particles. Or, 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 an embodiment of the present invention, in this crystallization step S10, crystallization is performed by switching the atmosphere a plurality of times in two stages of an oxidizing atmosphere and a non-oxidizing atmosphere. By switching the above atmosphere a plurality of times and adjusting appropriately, it is possible to control the size of the hollow portion of the particles when the porous structure is built and the ratio of the void portion when the porous structure is built.

By the way, the non-oxidizing atmosphere indicates 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 space inside the reaction vessel in such a non-oxidizing atmosphere, an inert gas such as nitrogen is circulated to the space inside the reaction vessel, and the inert gas is bubbled in the reaction solution. It can be mentioned to make it. The preferable flow rate of bubbling in the crystallization step S10 is 3 to 7 L / min, more preferably about 5 L / min.

On the other hand, the 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. As a means for maintaining the space inside the reaction vessel in such an oxidizing atmosphere, it is possible to circulate the atmosphere or the like to the space inside the reaction vessel, and to bubbling the atmosphere or the like in the reaction solution.

When constructing a porous structure, the atmosphere in the reaction vessel is controlled from an oxidizing atmosphere (usually, an oxygen concentration exceeding 21% by volume, for example, an air atmosphere) to an inert atmosphere or an oxygen concentration of 0.2% by volume or less. By changing the crystallization state by repeating the switching to the non-oxidizing atmosphere a plurality of times, the void ratio of the obtained metal composite hydroxide is increased to more than 50 to 80% (that is, larger than 50% and 80% or less). ) To produce a nickel-manganese-cobalt composite hydroxide having a porous structure. The number of times the crystallization treatment in which the atmosphere is changed is set by measuring the porosity, but the crystallization time in each crystallization treatment is in the range of 0.5 to 4 hours, and the total crystallization is performed. The time is in the range of 0.5 to 5 hours, and is appropriately adjusted from the size of the hydroxide particles, the size of the porosity, the thickness of the dense portion, and the like.

In this way, by controlling the atmosphere in the reaction vessel to a non-oxidizing atmosphere or an oxidizing atmosphere, the porosity of the secondary particles in the obtained metal composite hydroxide is controlled.

Although the nucleation step S11 and the particle growth step S12 have been described above, the above reaction atmosphere is controlled simultaneously while nucleation and particle growth are carried out.

[Porosity]
After embedding the nickel-manganese-cobalt composite hydroxide in the resin, the particles of the nickel-manganese-cobalt composite hydroxide are cut by argon sputtering using a cross section polisher (CP) to expose the particle cross section. The exposed particle cross section is observed using a scanning electron microscope, and the image of the observed particle cross section is analyzed by image analysis software with the voids of the image as black and the dense parts as white. The void ratio can be obtained by calculating the area of the black portion / (black portion + white portion) for the cross section of one or more particles.

<3-2. Cleaning process>
In the washing step S20, the transition metal composite hydroxide obtained in the crystallization step S10 is washed with a washing liquid.

[Cleaning liquid type]
In the cleaning step S20, cleaning is performed with a cleaning solution based on a carbonate, a hydrogen carbonate (bicarbonate), an alkali metal salt of a hydroxide, or an ammonium salt. 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 roots and chlorine roots, which are impurities, can be efficiently removed by utilizing a substitution reaction with carbonate ions and hydrogen carbonate ions (bicarbonate ions) in the cleaning liquid. You can. Further, by using a carbonate or a hydrogen carbonate (bicarbonate), it is possible to suppress the mixing of alkali metals such as sodium as compared with the case of using a hydroxide. In addition, when a hydroxide is used in a transition metal composite hydroxide having a void structure, it is difficult to remove impurities inside the particles, and in this respect as well, carbonates and hydrogen carbonates (bicarbonates) ) Is more effective.

As the carbonate, potassium carbonate is preferably selected, and as the hydrogen carbonate (bicarbonate), potassium hydrogen carbonate and ammonium hydrogen carbonate are preferably selected. In addition, by selecting an ammonium salt from carbonates and hydrogen carbonates (bicarbonates), cations such as sodium, potassium, calcium, and magnesium, which are impurities, can be replaced with ammonium ions in the cleaning solution. It can be used and removed efficiently. Furthermore, by selecting ammonium hydrogencarbonate (cheap ammonium bicarbonate) from the ammonium salts, cations such as sodium can be removed most efficiently.

This is because not only the substitution reaction between cations such as sodium and ammonium ions, but also the properties of ammonium hydrogen carbonate (ammonium bicarbonate), which is 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 hydrogen carbonate solution as a cleaning solution is 0.05 mol / L or more. If the concentration is less than 0.05 mol / L, the effect of removing impurities such as sulfate root, chlorine root and sodium may be reduced. Further, when the concentration is 0.05 mol / L or more, the effect of removing these impurities does not change. Therefore, if ammonium hydrogencarbonate (cheap bicarbonate) is added in excess, it affects the environmental load such as cost increase and wastewater standard, so it is preferable to set the upper limit concentration to about 1.0 mol / L.

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

[Liquid temperature]
The temperature of the ammonium hydrogen carbonate solution as the cleaning liquid is not particularly limited, but is preferably 15 to 50 ° C. When the liquid temperature is within the above range, the substitution reaction with impurities and the foaming 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 hydrogen carbonate solution as the cleaning liquid is preferably 1 to 20 L (the slurry concentration is 50 to 1000 g / L) with respect to 1 kg of the nickel-manganese-cobalt composite hydroxide. If it is less than 1 L, a sufficient effect of removing impurities may not be obtained. In addition, even if a liquid amount exceeding 20 L is used, the effect of removing impurities does not change, and an excessive liquid amount affects the environmental load such as cost increase and wastewater standard, which is a factor of the load increase of the wastewater amount in wastewater treatment. It also becomes.

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

[Washing method]
As a cleaning method, 1) a general cleaning method in which nickel-manganese-cobalt composite hydroxide is added to an ammonium hydrogen carbonate solution, slurried, stirred and washed, and then filtered, or 2) neutralization crystallization The slurry containing the nickel-manganese-cobalt composite hydroxide produced in the above can be supplied to a filter such as a filter press to pass an ammonium hydrogen carbonate solution through the liquid-passing cleaning. Liquid-passing cleaning is more preferable because it has a high effect of removing impurities, filtration and cleaning can be continuously performed in the same equipment, and productivity is high.

Further, after washing with an ammonium hydrogen carbonate solution, a washing liquid containing impurities washed out by the substitution reaction may adhere to the nickel-manganese-cobalt composite hydroxide, so it is preferable to wash with water at the end. Further, after washing with water, it is preferable to carry out a drying step (not shown) of drying the filtered water adhering to the nickel-manganese-cobalt composite hydroxide.

The nickel-manganese-cobalt composite hydroxide obtained through the cleaning step S20 is a secondary particle in which primary particles containing nickel, manganese, and cobalt are aggregated, or a positive electrode activity composed of the primary particles and the secondary particles. It is a nickel manganese cobalt composite hydroxide that is a precursor of the substance, and the sodium content of the nickel manganese cobalt composite hydroxide is less than 0.0005% by mass, and the nickel manganese cobalt composite hydroxide The void ratio of the particles is more than 50 to 80% (that is, greater than 50% and less than 80%).

According to the method for producing a nickel-manganese-cobalt composite hydroxide according to an embodiment of the present invention, it is possible to surely reduce the sodium content, and further improve the battery characteristics by increasing the void ratio and extending the life. It is possible to provide a method for producing a nickel-manganese-cobalt composite hydroxide, which is a precursor of a positive electrode active material capable of obtaining a lithium ion secondary battery.

<4. Lithium-ion secondary battery ＞
The lithium ion secondary battery according to the embodiment of the present invention is characterized by including a positive electrode containing the above-mentioned lithium nickel-manganese cobalt composite oxide. Further, the lithium ion secondary battery can be composed of the same components as a general lithium ion secondary battery, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. The embodiments described below are merely examples, and the lithium ion secondary battery of the present embodiment may be modified in various ways based on the embodiments described in the present specification and based on the knowledge of those skilled in the art. It can be carried out in an improved form. Further, the lithium ion secondary battery of the present embodiment is not particularly limited in its use.

(A) Positive electrode Using the lithium nickel manganese cobalt composite oxide which is the positive electrode active material described above, for example, a positive electrode of a lithium ion secondary battery is produced as follows. First, a powdered positive electrode active material, a conductive agent, and a binder are mixed, and if necessary, activated carbon, a solvent for viscosity adjustment or the like is added, and the mixture is kneaded to prepare a positive electrode mixture paste. The mixing ratio of each component in the positive electrode mixture paste is, for example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the positive electrode is the same as the positive electrode of a general lithium ion secondary battery. It is preferable that the content of the active material is 60 to 95 parts by mass, the content of the conductive agent is 1 to 20 parts by mass, and the content of the binder is 1 to 20 parts by mass.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like in order to increase the electrode density. In this way, a sheet-shaped positive electrode can be produced. The sheet-shaped positive electrode can be cut into an appropriate size according to the target battery and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the example, and other methods may be used.

As the conductive agent for the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, Ketjen black (registered trademark), and the like can be used.

The binder plays a role of binding the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylenepropylenediene rubber, styrenebutadiene, cellulose resin, polyacrylic. Acids and the like can be used.

If necessary, the positive electrode active material, the conductive agent, and the activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. Specifically, as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(B) Negative electrode For the negative electrode, a negative electrode mixture made into a paste by mixing a binder with a metallic lithium, a lithium alloy, or a negative electrode active material capable of occluding and desorbing lithium ions, and adding an appropriate solvent. Is applied to the surface of a metal foil current collector such as copper, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, a calcined product of an organic compound such as natural graphite, artificial graphite, or phenol resin, or a powdered material of a carbon substance such as coke can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and as a solvent for dispersing these active substances and the binder, N-methyl-2-pyrrolidone or the like can be used. An organic solvent can be used.

(C) Separator A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte. For example, a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used.

(D) Non-aqueous electrolyte A non-aqueous electrolyte solution can be used as the non-aqueous electrolyte. As the non-aqueous electrolyte solution, for example, one in which a lithium salt as a supporting salt is dissolved in an organic solvent may be used. Further, as the non-aqueous electrolyte solution, one in which a lithium salt is dissolved in an ionic liquid may be used. The ionic liquid is a salt composed of cations and anions other than lithium ions and showing a liquid state even at room temperature.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2-. One selected from ether compounds such as methyl tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more thereof may be mixed. Can be used.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant and the like.

Moreover, you may use a solid electrolyte as a non-aqueous electrolyte. The solid electrolyte has a property of being able to withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like is used.

The oxide-based solid electrolyte is not particularly limited, and any oxide-based solid electrolyte that contains oxygen (O) and has lithium ion conductivity and electron insulating properties can be used. Examples of the oxide-based solid electrolyte include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _X , LiBO ₂ N _X , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO _4- Li ₃ PO ₄ , Li ₄ SiO _4- Li ₃ VO ₄ , Li ₂ O-B ₂ O _3- P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O _3- ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≤ X ≤ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O _{4 and the} like can be mentioned.

The sulfide-based solid electrolyte is not particularly limited, and any sulfide-based solid electrolyte that contains sulfur (S) and has lithium ion conductivity and electron insulating properties can be used. Examples of the sulfide-based solid electrolyte include Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ S ₅ , LiI-Li _{2. S-B 2 S 3, Li} 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O ₅ , LiI-Li ₃ PO _4- P ₂ S _{5 and the} like can be mentioned.

As the inorganic solid based electrolyte may be used those other than the above, for _example, Li ₃ N, LiI, may be used Li 3 N-LiI-LiOH and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).

(E) Battery Shape and Structure The lithium ion secondary battery according to the embodiment of the present invention is composed of, for example, a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte as described above. Further, the shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical type and a laminated type can be used. Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte to form a positive electrode body and a positive electrode body that communicates with the outside. A lithium ion secondary battery is completed by connecting the terminals and the negative electrode current collector and the negative electrode terminals communicating with the outside using a current collecting lead or the like and sealing the battery case.

The lithium ion secondary battery according to the embodiment of the present invention is provided with a positive electrode composed of the above-mentioned positive electrode active material, whereby the sodium content is surely reduced, sintering aggregation is suppressed, and high. It is possible to further improve the battery characteristics by increasing the porosity and extending the life.

Next, a method for producing a nickel-manganese-cobalt composite hydroxide, a nickel-manganese-cobalt composite hydroxide, a lithium-nickel-manganest-cobalt composite oxide, and a lithium ion secondary battery according to an embodiment of the present invention will be described in more detail with reference to Examples. To do. The present invention is not limited to these examples.

In Examples 1 to 13 and Comparative Examples 1 to 9, the transition metal composite hydroxide obtained in the crystallization step was recovered as a precursor nickel-manganese-cobalt composite hydroxide through washing, filtering, and drying operations. After that, various analyzes were performed by the following methods.

[Composition, calcium and magnesium content]
The composition, calcium and magnesium contents were analyzed by acid decomposition-ICP emission spectroscopic analysis, and ICPE-9000 (manufactured by Shimadzu Corporation), which is a multi-type ICP emission spectroscopic analyzer, was used for the measurement.

[Sodium and potassium content]
The sodium and potassium contents were analyzed by an acid decomposition-atomic absorption spectrometry method, and an atomic absorption spectrophotometer 240AA (manufactured by Azilent Technology Co., Ltd.), which is an atomic absorption spectrometer, was used for the measurement.

[Sulfate content]
Sulfate ion content was analyzed for total sulfur content in the acid-decomposable -ICP emission spectroscopy, the total sulfur content was determined by converting the sulfate radical (SO 4 ^_2-). An ICPE-9000 (manufactured by Shimadzu Corporation), which is a multi-type ICP emission spectroscopic analyzer, was used for the measurement.

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

[Average particle size and particle size distribution]
The average particle size (MV) and particle size distribution [(d90-d10) / average particle size] were determined from the volume reference distribution measured by the laser diffraction / scattering method. For the measurement, a laser diffraction / scattering type particle size distribution measuring device, Microtrack MT3300EXII (manufactured by Microtrack Bell Co., Ltd.) was used.

[Specific surface area]
The specific surface area was analyzed by the nitrogen gas adsorption / desorption method by the BET 1-point method, and the measurement was performed using the MacSorb 1200 series (manufactured by Mountech Co., Ltd.), which is a gas flow type specific surface area measuring device.

[Porosity]
For the void ratio, a cross section polisher IB-19530CP (manufactured by JEOL Ltd.), which is a cross-section preparation device, is used for cutting the sample particles, and a Schottky field emission type scanning is used for observing the cross section. A JSM-7001F (manufactured by JEOL Ltd.), which is a scanning electron microscope SEM-EDS, was used. Furthermore, with WinRof6.1.1 (manufactured by Mitani Shoji Co., Ltd.), which is image analysis / measurement software, the voids in the particle cross section are measured as black, and the dense parts of the particles are measured as white. The void ratio was obtained by calculating the area of the black portion / (black portion + white portion) with respect to the particles of.

[Manufacturing and evaluation of positive electrode active material]
Further, the lithium metal composite oxide, more specifically, the 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 methods. Was done.

[A, Manufacture of positive electrode active material]
The precursor nickel-manganese-cobalt composite hydroxide was heat-treated at 700 ° C. for 6 hours in an air (oxygen: 21% by volume) stream to recover the metal composite oxide. Subsequently, lithium hydroxide, which is a lithium compound, was weighed so that Li / Me = 1.025 and mixed with the recovered metal composite oxide to prepare a lithium mixture. A shaker mixer device (TURBULA-TypeT2C manufactured by Willie et Bacoffen (WAB)) was used for the mixing operation.

Next, the prepared lithium mixture was 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 crushed, and lithium nickel-manganese cobalt cobalt. A composite oxide was obtained.

[B, Evaluation of positive electrode active material]
In the obtained lithium nickel-manganese-cobalt composite oxide, the above-mentioned analysis method and the above-mentioned analysis method are used for analysis of sodium content, potassium content, calcium content, magnesium content, sulfate root content, chlorine root content, and void ratio. Analytical equipment was used. The Me-seat occupancy, which indicates the crystallinity of the lithium nickel-manganese-cobalt composite oxide, was calculated by performing Rietveld analysis on 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 seat occupancy rate indicates the abundance ratio of the metal element in the metal layer (Me seat) of the layered structure in which nickel, manganese, cobalt and the additive element M of the lithium nickel manganese cobalt composite oxide. The Me seat occupancy rate correlates with the battery characteristics, and the higher the Me seat occupancy rate, the better the battery characteristics.

Hereinafter, each condition of Examples and Comparative Examples will be described.

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

An appropriate amount of 25% aqueous sodium hydroxide solution and 25% aqueous ammonia as an ammonium ion feeder 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 12.8. 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 raw material solution of 2.0 mol / L. In this raw material solution, the element molar ratio of each metal was adjusted to be Ni: Mn: Co = 1: 1: 1. Further, 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 ⁻ ] becomes 0.025 to prepare an alkaline solution. Made.

The raw material solution is added to the reaction solution in the reaction vessel at 12.9 mL / min, and the ammonium ion feeder and alkaline solution are also added to the reaction solution at a constant rate to increase the ammonium ion concentration in the reaction solution to 10 g / min. Nucleation was carried out by controlling the pH to 12.8 (nucleation step pH) and carrying out crystallization for 2 minutes and 30 seconds while the pH was maintained at L.

Then, 64% sulfuric acid was added until the pH of the reaction solution reached 11.6 (particle growth step pH) as the pH measured based on the liquid temperature of 25 ° C. As the pH to be measured based on the liquid temperature of 25 ° C., after the pH of the reaction solution reached 11.6, the supply of the raw material solution, the ammonium ion feeder, and the alkaline solution was restarted, and the pH was kept controlled at 11.6. , Crystallization was continued for 4 hours and particle growth was carried out to obtain a transition metal composite hydroxide.

Regarding the reaction atmosphere, first, the inside of the reaction vessel was set to an air atmosphere (oxygen concentration: 21% by volume), and after holding for 0.5 hours from the start of crystallization, the raw material solution, ammonia water, and alkaline solution were once supplied. Stop and circulate and replace nitrogen gas at a flow rate of 5 L / min until the oxygen concentration in the reaction vessel space is 0.2% by volume or less, and then supply the solution after the oxygen concentration is 0.2% by volume or less. It was restarted and crystallization was continued. Further, the crystallization treatment was continued for a total of 4 hours while switching the reaction atmosphere in the reaction vessel to a non-oxygen atmosphere of 0.2% by volume or less and an air atmosphere a plurality of times. Here, the number of switchings is set to 5. The details of the number of switchings of 5 are as follows: air atmosphere (oxidizing atmosphere), non-oxygen atmosphere (non-oxidizing atmosphere), air atmosphere (oxidizing atmosphere), non-oxygen atmosphere (non-oxidizing atmosphere), air atmosphere (non-oxidizing atmosphere) Oxidizing atmosphere) and non-oxygen atmosphere (non-oxidizing atmosphere).

The obtained transition metal composite hydroxide is solid-liquid separated by a filter press filter, and then an ammonium hydrogen carbonate solution having a concentration of 0.05 mol / L is used as the cleaning solution, and the cleaning solution is used for 1 kg of the transition metal composite hydroxide. The impurities were removed by passing the liquid through a filter press filter at a ratio of 5 L, and then water was further passed and washed with water. Then, the water adhering to the transition metal composite hydroxide washed with water was dried to obtain a nickel-manganese-cobalt composite hydroxide as a precursor.

(Example 2)
In Example 2, when nickel sulfate, manganese sulfate, and cobalt chloride are dissolved in water to prepare a raw material solution of 2.0 mol / L, the molar ratio of nickel, manganese, and cobalt in the raw material solution is 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 are dissolved in water to prepare a raw material solution of 2.0 mol / L, the molar ratio of nickel, manganese, and cobalt in the raw material solution is 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 the alkaline solution was prepared. 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 the alkaline solution was adjusted so that [CO ₃ ^2- ] / [OH ⁻ ] was 0.048. 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 of the nucleation step was set 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 of 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 of the particle growth step was set 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 of the particle growth step was set to 10.6.

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

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

(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 a cleaning solution.

(Comparative Example 1)
In Comparative Example 1, when nickel sulfate, manganese sulfate, and cobalt chloride were dissolved in water to prepare a raw material solution of 2.0 mol / L, the molar ratio of nickel, manganese, and cobalt in the raw material solution was Ni: Mn: Co. Nickel manganese cobalt in the same manner as in Example 1 except that it was adjusted to be 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, using only sodium hydroxide to adjust the alkaline ^{_{solution, [CO 3 2-] / [}} OH -] except that the manner not consider, in the same manner as in Example 1, nickel manganese cobalt composite water 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 the alkaline solution was prepared. 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 the [CO ₃ ^2- ] / [OH ⁻ ] was adjusted to 0.055 when the alkaline solution was adjusted. 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 cleaning step was omitted and cleaning with an 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 hydrogencarbonate solution having a concentration of 0.02 mol / L was used as a cleaning solution.

(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 the ammonium carbonate solution was used as a cleaning solution.

(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 the sodium hydrogen carbonate solution was used as a cleaning solution.

(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 the sodium carbonate solution was used as a cleaning solution.

The above conditions and results are shown in Table 1, Table 2 and Table 3.

(Comprehensive evaluation)
As shown in Tables 1, 2 and 3, in Examples 1 to 13, the conditions of the crystallization step and the washing step were all within the preferable range in the nickel manganese cobalt composite hydroxide as the precursor. .. Therefore, not only the nickel-manganese-cobalt composite hydroxide but also the lithium-nickel-manganese-cobalt composite oxide, which is a positive electrode active material, has a sodium content, a sulfate root content, and a chlorine root content in removing impurities. In addition, the potassium, calcium, and magnesium contents were sufficiently reduced. Further, in the lithium nickel-manganese-cobalt composite oxide, the Me-seat occupancy rate exceeds 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, with all the example data being less than the lower limit of quantification (analysis) (0.0005% by mass). In addition, the same results as for sodium were obtained for potassium, calcium, and magnesium. Therefore, in the positive electrode active material, the MV ratio, which is an index of sintering and aggregation, is in the range of 0.95 to 1.05 without the sodium and the like being dissolved in the lithium sites, and is randomly selected. When 100 or more selected particles were observed with a scanning electron microscope, the number of observed aggregation of secondary particles was 5% or less of the total number of observed secondary particles.

Here, the lower limit of quantification means the minimum amount or the minimum concentration at which the target component can be analyzed (quantitated) by a certain analysis method. Further, 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 reliability is guaranteed in the signal of the target component obtained by the measurement is called the measurement lower limit. Further, in the process of preparing the analysis sample into the measurement sample solution, the lower limit of quantification is obtained by multiplying the lower limit of measurement by the dilution factor indicating how much the original analysis sample is concentrated or diluted.

That is, for example, the sodium content and potassium content in the present invention are prepared by acid-decomposing 1 g of the analysis sample to 100 mL of the measurement sample solution with respect to the lower limit of 0.05 μg / mL of the measurement of the atomic absorption spectrometer (dilution ratio is Since it was 100 times), the lower limit of quantification is 5 ppm (μg / g), that is, 0.0005 mass%. In addition, the calcium content and magnesium content in the present invention are prepared by acid-decomposing 1 g of the analysis sample to 100 mL of the measurement sample solution with respect to the lower limit of 0.05 μg / mL of the measurement of the ICP emission spectrophotometer (dilution ratio is 100). The lower limit of quantification is 5 ppm (μg / g), that is, 0.0005% by mass.

On the other hand, in Comparative Examples 1 to 9, in making an alkaline solution ^{_{[CO 3 2-] / [OH}} -] and the concentration of ammonium bicarbonate solution is wash or not a preferable range carbonate Since a cleaning solution other than the ammonium hydrogen hydrogen solution was used and the conditions deviated from the optimum conditions, the excellent effect as in the examples could not be obtained.

Further, in Examples 1 to 13, in addition to the nickel-manganese-cobalt composite hydroxide, the porous structure of the lithium nickel-manganese-cobalt composite oxide also has a void ratio of more than 50 to 80% (that is, greater than 50% and 80% or less). When used as a positive electrode active material, the particle strength is kept within an allowable range to prolong the life of the particles without excessively reducing the bulk density, and the contact area between the positive electrode active material and the electrolytic solution is sufficient. It was possible to make it, and the battery characteristics were improved.

Based on the above, lithium nickel manganese cobalt, which is a positive electrode active material capable of reliably reducing the sodium content, suppressing sintering aggregation, and further improving battery characteristics by increasing the void ratio and extending the life. It was possible to provide a composite oxide and a lithium ion secondary battery.
By the way, for example, in the field of analytical chemistry, reagent manufacturers that provide standard substances for analysis and testing are working on further purification of standard substances every day to reduce impurities as much as possible. Research is being conducted. From this, it can be said that the lithium nickel-manganese-cobalt composite oxide disclosed in the present invention, in which the content of impurities such as sodium is reduced as much as possible, is not merely a modification of the design items. Needless to say, it is clear.

Although each embodiment and each embodiment of the present invention have been described in detail as described above, those skilled in the art can understand that many modifications that do not substantially deviate from the novel matters and effects of the present invention are possible. , Will be easy to understand. Therefore, all such modifications are included in the scope of the present invention.

For example, a term described at least once in a specification or drawing with a different term in a broader or synonymous manner may be replaced by that different term anywhere in the specification or drawing. Further, the configuration and operation of the lithium nickel-manganese-cobalt composite oxide and the lithium ion secondary battery are not limited to those described in each embodiment and each embodiment of the present invention, and various modifications can be carried out.

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

Claims (5)

Secondary particles in which primary particles containing lithium, nickel, manganese, and cobalt are aggregated, or lithium nickel-manganese-cobalt composite oxide composed of the primary particles and the secondary particles.
The sodium content of the lithium nickel-manganese-cobalt composite oxide is less than 0.0005% by mass.
The porosity of the particles of the lithium nickel-manganese-cobalt composite oxide is more than 50 to 80%.
The ratio obtained by dividing the average particle size of the lithium nickel-manganese-cobalt composite oxide by the average particle size of the nickel-manganese-cobalt composite hydroxide as a precursor is 0.95 to 1.05. Nickel manganese cobalt composite oxide. When 100 or more randomly selected particles of the lithium nickel-manganese cobalt composite oxide are observed with a scanning electron microscope, the number of secondary particles observed to be aggregated is the total number of secondary particles observed. The lithium nickel manganese cobalt composite oxide according to claim 1, wherein the content is 5% or less. The sulfate root content contained in the lithium nickel manganese cobalt composite oxide is 0.15% by mass or less, the chlorine root content is 0.005% by mass or less, and the Me seat occupancy rate is 93.0% or more. The lithium nickel-manganese-cobalt composite oxide according to claim 1 or 2. Any of claims 1 to 3, wherein the content of at least one or more of potassium, calcium, and magnesium contained in the lithium nickel-manganese-cobalt composite oxide is less than 0.0005% by mass. The lithium nickel manganese cobalt composite oxide according to item 1. A lithium ion secondary battery comprising at least a positive electrode containing the lithium nickel-manganese-cobalt composite oxide according to any one of claims 1 to 4.