JP7064685B2 - A method for producing a nickel-manganese composite hydroxide and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. - Google Patents

Description

The present invention relates to a method for producing a nickel-manganese composite hydroxide and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook personal computers, there is a strong demand for the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density. A typical example of such a non-aqueous electrolyte secondary battery is a lithium ion secondary battery. Lithium metal, lithium alloy, metal oxide, carbon or the like is used as the negative electrode active material of the lithium ion secondary battery. These materials are materials capable of desorbing and inserting lithium.

Currently, research and development of lithium-ion secondary batteries is being actively carried out. Among these, a lithium ion secondary battery using a lithium transition metal composite oxide, particularly a lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, as a positive electrode active material can obtain a high voltage of 4V class. It is expected and put into practical use as a battery with high energy density. In addition, lithium nickel composite oxide (LiNiO ₂ ) and lithium nickel cobalt manganese composite oxide (LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ) using nickel, which is cheaper than cobalt, as the positive electrode active material, etc. Development is also underway. Among them, lithium nickel cobalt manganese composite oxide is attracting attention because it has an excellent balance of capacity, output characteristics, durability, cost, and the like. However, since the capacity is inferior to that of the lithium-nickel composite oxide system, it is required to improve the capacity (energy density).

In many cases, the above-mentioned positive electrode active material is used properly depending on the application and required characteristics of the lithium ion secondary battery. For example, in electric vehicle (BEV) applications, a long cruising range is required, so a high-capacity positive electrode active material is required. On the other hand, in plug-in hybrid vehicle (PHEV) applications, a positive electrode active material having a good balance between capacity and output characteristics is often required. With the increasing variety of batteries designed in this way, various material designs are required for the positive electrode active material.

Various proposals have been made in response to various material design requirements for positive electrode active materials. For example, in Patent Document 1, in order to improve the cycle characteristics and increase the output, the average particle size is 2 to 8 μm, which is an index showing the spread of the particle size distribution [(d90-d10) / average particle size]. A positive electrode active material for a non-aqueous electrolyte secondary battery having a value of 0.60 or less has been proposed. Such an active material is characterized by a high capacity and a long life because an electrochemical reaction occurs uniformly, but on the other hand, it is said that the volume energy density is high because the filling property of the active material is low. I can't say.

Further, for example, in Patent Document 2, a hydroxide raw material powder is crushed to prepare a slurry containing a crushed raw material powder having a specific particle size distribution, and a substantially spherical granulated powder is prepared using this slurry. A method for producing a positive electrode active material for a lithium ion battery has been proposed in which a lithium compound is mixed and the granulated powder and the lithium compound are reacted by firing. As a result, it is possible to obtain a positive electrode active material having a desired porosity and a high open pore ratio, which brings about high battery characteristics. However, a step of pulverizing the obtained hydroxide and then granulating it again to obtain a precursor is required, which causes a problem in productivity. Further, since the open pore ratio changes depending on the crushing condition, it cannot be said that the open pore ratio can be easily controlled.

Further, for example, in Patent Document 3, a lithium transition metal composite oxide is passed through a classifier to separate a large particle size and a small particle size, and the large particle size and the small particle size are separated by a weight ratio of 0: 100. A method for producing a positive electrode material for a lithium secondary battery, which is blended at ~ 100: 0, has been proposed. As a result, it is possible to easily manufacture positive electrode materials for lithium secondary batteries with various balances of rate characteristics and capacity. However, since the lithium transition metal composite oxide is classified, remixed and mixed, the number of steps increases and the productivity decreases. In addition, there is a possibility that the lithium transition metal composite oxide having one of the classified particle sizes remains.

On the other hand, in Patent Document 4, the outer shell portion has an average particle size of more than 8 μm and 16 μm or less, and [(d90-d10) / average particle size], which is an index showing the spread of the particle size distribution, is 0.60 or less. And a positive electrode active material for a non-aqueous electrolyte secondary battery, which is composed of a hollow portion existing inside the hollow portion, has been proposed. It is said that this positive electrode active material has a uniform particle size distribution and good filling property, and can reduce the value of positive electrode resistance. However, although hollow particles can obtain high output characteristics, there is a problem that the filling property is lowered. Further, although the shape of the primary particle of the hydroxide is controlled by switching the atmosphere at the time of crystallization, there is a problem that the productivity is lowered because the switching takes time.

Further, in Patent Document 5, a reaction aqueous solution is formed by supplying an aqueous solution containing at least nickel and manganese, an aqueous solution containing an ammonium ion feeder, and an alkaline solution into a reaction vessel and mixing them to form the nickel. When crystallizing manganese composite hydroxide particles, the oxygen concentration in the reaction vessel should be 3.0% by volume or less, the temperature of the reaction aqueous solution should be 35 ° C to 60 ° C, and the nickel ion concentration should be 1000 mg / L or more. A controlled method for producing nickel-manganese composite hydroxide particles has been proposed. As a result, the circularity of the nickel-manganese composite hydroxide particles can be improved, and the filling property of the positive electrode active material using the nickel-manganese composite hydroxide particles as a precursor can be improved. However, this proposal focuses only on the filling property improved by the sphericity of the particles, and does not examine the output characteristics.

Japanese Unexamined Patent Publication No. 2011-116580 JP-A-2015-76397 Japanese Patent Application Laid-Open No. 2003-051311 International release WO2012 / 169274 International release WO2015 / 115547

As described above, the performance required for non-aqueous electrolyte secondary batteries is diversified, and various positive electrode active materials have been proposed in order to meet such diversified demands. At present, no method for producing a positive electrode active material having appropriately controlled output characteristics and high productivity has been developed. Further, the filling property and the output characteristics of the positive electrode active material can be improved, for example, by achieving both the tap density and the specific surface area of the metal composite hydroxide which is the precursor of the positive electrode active material at a high level. Therefore, although various methods for producing a metal composite hydroxide have been studied, a precursor of a positive electrode active material that can sufficiently meet the diversifying required characteristics of a non-aqueous electrolyte secondary battery on an industrial scale has been studied. No manufacturing method has been developed.

In view of the above problems, the present invention is used as a precursor of a positive electrode active material by easily controlling the average particle size and sparse density of the nickel-manganese composite hydroxide within a desired range. , A method for producing a nickel-manganese composite hydroxide that can easily meet various demands on the performance of a secondary battery on an industrial scale, and a non-use of the nickel-manganese composite hydroxide. It is an object of the present invention to provide a method for producing a positive electrode active material for an aqueous electrolyte secondary battery.

The present inventors diligently studied a method for producing a nickel-manganese composite hydroxide as a precursor of a positive electrode active material, and found that the concentration of dissolved nickel in the reaction aqueous solution in the crystallization step, the concentration of dissolved oxygen, and the reaction aqueous solution were obtained. It is possible to control the particle size and sparse density of the obtained hydroxide within a desired range by the stirring power to be loaded, and a non-aqueous electrolyte using a positive electrode active material using this hydroxide as a precursor. The present invention was completed based on the finding that the capacity and output characteristics of the next battery can be easily controlled.

In the first aspect of the present invention, the general formula (1): Ni _x Mn _y M _z (OH) _{2 + α} (in the above formula (1), M is Co, Ti, V, Cr, Zr, Nb, Mo, At least one additive element selected from Hf, Ta, Fe, and W, where x is 0.1 ≦ x ≦ 0.9, y is 0.05 ≦ y ≦ 0.8, and z is. 0 ≦ z ≦ 0.8, satisfying x + y + z = 1.0, and α is represented by 0 ≦ α ≦ 0.4), and is composed of secondary particles in which a plurality of primary particles are aggregated. A method for producing a nickel-manganese composite hydroxide, which comprises a crystallization step of neutralizing salts containing at least nickel and manganese in a reaction aqueous solution to form a nickel-manganese composite hydroxide. Includes a step of continuously adding a mixed aqueous solution containing nickel and manganese to the reaction vessel and overflowing a slurry containing nickel-manganese composite hydroxide particles produced by neutralization to recover the particles. Based on the relationship that the dissolved oxygen concentration has a positive correlation with the sparse density at any volume average particle size, and the dissolved nickel concentration and the stirring power each have a negative phase. , The dissolved oxygen concentration in the reaction aqueous solution is within the range of 0.2 mg / L or more and 8.0 mg / L or less, the fluctuation range is within the range of ± 0.2 mg / L, and the dissolved nickel concentration is 10 mg / L or more and 1500 mg. By adjusting the stirring power applied to the reaction aqueous solution within the range of 0.5 kW / m ³ or more and 15 kW / m ³ or less , the volume average particle size is within the range of 5 μm or more and 20 μm or less. And , the sparse density represented by [(void area inside the secondary particle / cross-sectional area of the secondary particle) × 100] (%) is desired within the range of 0.5% or more and 40% or less . Provided is a method for producing a nickel-manganese composite hydroxide , which is controlled in a range.

Further, the sparse density is preferably controlled by adjusting at least the dissolved oxygen concentration and the dissolved nickel concentration. Further, the average particle size is preferably controlled by adjusting at least the dissolved nickel concentration and the stirring power .

Further, in the crystallization step, the temperature of the reaction aqueous solution is preferably in the range of 35 ° C. or higher and 60 ° C. or lower. Further, in the crystallization step, the pH value measured based on the liquid temperature of the reaction aqueous solution at 25 ° C. is preferably in the range of 10.0 or more and 13.0 or less . Further , it is preferable that the nickel-manganese composite hydroxide is controlled in a volume average particle size of 5 μm or more and 20 μm or less and an average sparse density of 0.5% or more and 40% or less . Further , it is preferable that the secondary particles have [(D90-D10) / volume average particle size], which is an index indicating the spread of the particle size distribution, of 0.7 or more.

In the second aspect of the present invention, the general formula (2): Li _{1 + t} Ni _x Mn _y M _z O _{2 + β} (in the formula (2), M is Co, Ti, V, Cr, Zr, Nb, Mo, Hf. , Ta, Fe, W, at least one additive element, t is −0.05 ≦ t ≦ 0.5, x is 0.1 ≦ x ≦ 0.9, y. Is 0.05 ≦ y ≦ 0.8, z is 0 ≦ z ≦ 0.8, and x + y + z = 1.0 is satisfied, and β is 0 ≦ β ≦ 0.5). It is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is represented and contains a lithium nickel-manganese composite hydroxide composed of secondary particles in which primary particles are aggregated, and is a nickel-manganese composite obtained by the above-mentioned production method. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a step of mixing a hydroxide and a lithium compound to obtain a mixture and a step of firing the mixture to obtain a lithium nickel-manganese composite oxide. Provided.

Since the nickel-manganese composite hydroxide obtained by the production method of the present invention has an average particle size and a sparse density in a desired range, the performance of the secondary battery when used as a precursor of a positive electrode active material It is possible to easily meet the various demands of the above on an industrial scale. In addition, the production method of the present invention can easily and highly productively produce the nickel-manganese composite hydroxide and the positive electrode active material using the same. Therefore, it can be said that the industrial value of the present invention is extremely high.

FIG. 1 is a diagram showing an example of a method for producing a nickel-manganese composite hydroxide. FIG. 2 is a schematic diagram showing an example of a nickel-manganese composite hydroxide. FIG. 3 is a photograph showing an example of the appearance and cross section of the nickel-manganese composite hydroxide (Examples 1 to 4). FIG. 4 is a graph showing an example of the average sparse density, the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power of the nickel-manganese composite hydroxide (Examples 1 to 6). FIG. 5 is a photograph showing another example of the appearance and cross section of the nickel-manganese composite hydroxide (Examples 11 to 13). FIG. 6 is a graph showing other examples of the average sparse density, the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power of the nickel-manganese composite hydroxide (Examples 11 to 13). FIG. 7 is a diagram showing an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

Hereinafter, referring to the drawings, the method for producing a nickel-manganese composite hydroxide of the present embodiment, the nickel-manganese composite hydroxide obtained by the production method, and a non-aqueous electrolyte using the nickel-manganese composite hydroxide. The details of the method for producing a positive electrode active material for a secondary battery will be described. In the drawings, in order to make each configuration easy to understand, a part is emphasized or a part is simplified, and the actual structure or shape, scale, etc. may be different.

(1) Method for Producing Nickel-Manganese Composite Hydroxide FIG. 1 is a diagram showing an example of the method for producing a nickel-manganese composite hydroxide according to the present embodiment. FIG. 2 is a schematic diagram showing an example of a nickel-manganese composite hydroxide obtained by the production method. As shown in FIG. 2, the nickel-manganese composite hydroxide 1 (hereinafter, also referred to as “composite hydroxide 1”) is composed of secondary particles 3 in which a plurality of primary particles 2 are aggregated. The secondary particles 3 have voids 4 between the primary particles 2. Hereinafter, when FIG. 1 is described, FIG. 2 will be referred to as appropriate.

As shown in FIG. 1, the method for producing the composite hydroxide 1 of the present embodiment is a crystal in which a salt containing at least nickel and manganese is neutralized and co-precipitated in the reaction aqueous solution in the crystallization reaction tank. Includes analysis step. In the present embodiment, it is important to adjust the dissolved nickel concentration in the reaction aqueous solution, the dissolved oxygen concentration, and the stirring power loaded on the reaction aqueous solution during this crystallization step. By adjusting these factors (parameters), it is possible to control the particle size d and the sparse density of the obtained composite hydroxide 1 (secondary particles 3), respectively. By using the composite hydroxide 1 obtained by controlling the particle size d and the sparse density within a desired range as the precursor of the positive electrode active material, it is desired to balance the battery capacity and the output characteristics of the positive electrode active material. It is possible to design within the range.

Here, the "particle size" means, for example, the volume average particle size MV measured by a laser diffraction / scattering type particle size distribution measuring device or the like. Further, the "sparse density" is obtained from, for example, an image analysis of an SEM image of a cross section of one composite hydroxide particle [(area of void 4 inside secondary particle 3 / cross section of secondary particle 3). ) × 100] (%). For example, in the cross section of the composite hydroxide 1 particle shown in FIG. 2, the sparse density is represented by [(area of void 4) / (sum of cross section of primary particle 2 and area of void 4) × 100]. Is the value to be. That is, the higher the sparse density, the sparser the structure inside the secondary particles 3, and the lower the sparse density, the denser the inside of the secondary particles 3. For the sparse density, for example, the sparse density of the cross section of 20 secondary particles 3 having 80% or more of the volume average particle size (MV) is measured, and the average sparse density, which is the average value thereof, is used. Can be done.

FIG. 3 shows the appearance (FIGS. 3A, C, E, G) and the cross section (FIGS. 3B, D, F, H) of the composite hydroxide 1 obtained by adjusting the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power. It is a photograph of SEM showing an example of. In FIGS. 3A to 3H, the values of the average sparse density are shown in ascending order from the upper row to the lower row (FIGS. 3A and B: average sparse density 1.8%, FIGS. 3C and D: average sparse density 4.1). %, FIGS. 3E, F: average sparse density 19%, FIG. 3G, H: average sparse density 24.8%). Further, FIG. 4 is a graph showing an example of the relationship between the sparse density, the dissolved nickel concentration, the dissolved oxygen concentration, and the stirring power at the average particle size of any secondary particle 3. Note that FIG. 3 corresponds to the composite hydroxide 1 obtained in Examples 1 to 4 described later, and FIG. 4 corresponds to the results obtained in Examples 1 to 6. Hereinafter, the relationship between the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power with respect to the particle size d and the sparse density of the composite hydroxide 1 (secondary particles 3) will be described with reference to FIGS. 3 and 4 as appropriate. ..

Since the composite hydroxide 1 uses a salt containing manganese in the crystallization step, its morphology is greatly affected by the dissolved oxygen concentration in the reaction aqueous solution. For example, in the crystallization step, when the dissolved oxygen concentration is lower, the primary particles 2 have a thick plate-like shape (for example, FIGS. 3A to 3D). The composite hydroxide 1 composed of the primary particles 2 having a thick plate-like shape tends to have a low sparse density. On the other hand, when the dissolved oxygen concentration is higher, the primary particles 2 have a fine needle-like or thin plate-like shape (for example, FIGS. 3E to 3H). The composite hydroxide 1 composed of the secondary particles 3 in which the primary particles 2 having a fine needle-like or thin plate-like shape are aggregated tends to have a high sparse density. Therefore, by appropriately adjusting the dissolved oxygen concentration, the morphology (shape) of the primary particles 2 can be controlled, and as a result, the sparse density of the secondary particles 3 can be controlled. The term "morphology" refers to the form and structure of the primary particles 2 and / or the secondary particles 3, including the shape, thickness (aspect ratio), average particle size, particle size distribution, crystal structure, tap density, etc. of the particles. It is a characteristic involved.

For example, as shown in FIGS. 4A and 4B, it is possible to form secondary particles 3 having a high sparse density by adjusting the dissolved oxygen concentration to a high level under specific conditions, and to adjust the dissolved oxygen concentration to a low level. By doing so, it is possible to form secondary particles 3 having a low sparse density. That is, the dissolved oxygen concentration (eg, FIG. 4B) can have a positive correlation with the sparse density (eg, FIG. 4A).

However, in the crystallization step, for example, when the dissolved oxygen concentration is adjusted to be high in order to increase the sparse density, the primary particles 2 become too fine, and the secondary particles 3 in which such primary particles 2 are aggregated become , It may be difficult to maintain its shape. Further, even in the primary particles 2 having the same shape obtained by adjusting the dissolved oxygen concentration, the sparse density may fluctuate depending on the arrangement of the primary particles 2, and it is desired to adjust the dissolved oxygen concentration alone. It is difficult to accurately control the sparse density of the composite hydroxide 1 in a wider range in terms of particle size. In particular, when the composite hydroxide 1 is used as a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, may be referred to as “positive electrode active material”), the positive electrode activity has good battery capacity and output characteristics. In order to obtain a substance, it is necessary to have an excellent balance of the specific surface area and tap density of the composite hydroxide 1, but simply adjusting the dissolved oxygen concentration is a good morphology (secondary) as a precursor of the positive electrode active material. The composite hydroxide 1 having the particle size and sparse density of the particles) may not be obtained.

Therefore, as a result of diligent studies on the production conditions of the composite hydroxide 1, the present inventors further adjusted the dissolved nickel concentration in the reaction aqueous solution and the stirring power loaded on the reaction aqueous solution in addition to the above-mentioned dissolved oxygen concentration. By doing so, it was found that the morphology of the primary particle 2 and the secondary particle 3 can be accurately controlled in a wider range. That is, the production method of the present embodiment produces a nickel-manganese composite hydroxide that is suitably used as a precursor of a positive electrode active material by adjusting the dissolved nickel concentration and the stirring power according to the dissolved oxygen concentration. It is possible to do.

That is, when the dissolved oxygen concentration is adjusted to a higher range and other factors (parameters) are not particularly adjusted, the primary particles 2 may become too fine and it may be difficult to form the secondary particles 3. For example, by adjusting the concentration of dissolved nickel to a lower level, the precipitation rate of the primary particles 2 becomes high, and the secondary particles 3 having a sparse structure in which these primary particles 2 are aggregated can be stably formed. .. On the other hand, when the dissolved oxygen concentration is adjusted to a lower range, for example, by adjusting the dissolved nickel concentration to a higher level, the precipitation rate of the primary particles 2 becomes low, and the voids 4 between the primary particles 2 are filled. When the thickness of the primary particles 2 is further increased to form the secondary particles 3 having a dense structure and the dissolved nickel concentration is adjusted to a higher range, the particle size of the secondary particles 3 is coarse. It is possible to suppress the change.

Further, by controlling the aggregated state of the primary particles 2 by the stirring power, the particle size of the secondary particles 3 can be controlled more accurately in a wide range. That is, when the dissolved oxygen concentration is adjusted to a higher range, for example, by adjusting the stirring power to a lower level, the secondary particles 3 can be grown while suppressing the destruction of the secondary particles 3 due to stirring. Therefore, even a composite hydroxide 1 composed of secondary particles 3 composed of primary particles 2 having a needle-like or thin plate-like shape can have a larger particle size. On the other hand, when the dissolved oxygen concentration is adjusted to a lower range, the coarse growth of the secondary particles 3 due to the aggregation of the primary particles 2 can be suppressed by adjusting the stirring power to a higher range. Further, by suppressing the coarsening of the secondary particles 3, the precipitation of the composite hydroxide in the secondary particles 3 is promoted, and the secondary particles 3 can be made denser.

Hereinafter, a preferable example of adjusting the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power will be described with reference to FIG. For example, as shown in FIGS. 4B-4D, when the dissolved oxygen concentration (FIG. 4B) is adjusted higher, the dissolved nickel concentration (FIG. 4C) and the stirring power (FIG. 4D) are adjusted to be further reduced. Therefore, it is possible to control the sparse density (for example, about 0.4% or more and 55%) in a wider range (for example, about 0.4% or more) (FIG. 4A) in a constant particle size (for example, about 10 μm). In this case, the dissolved nickel concentration and the stirring power each have a negative phase with respect to the sparse density. That is, by adjusting the dissolved nickel concentration according to the dissolved oxygen concentration, the sparse density and the particle size d of the secondary particles 3 can be precisely controlled in a wider range.

Further, FIGS. 5 and 6 are examples corresponding to FIGS. 3 and 4, respectively, when the composition of the composite hydroxide 1 is different from that of FIGS. 3 and 4, respectively. 3 and 4 are examples in which the composition of the composite hydroxide 1 satisfies Ni: Co: Mn (molar ratio (atomic number%)) = 0.35: 0.35: 0.30). .. 5 and 6 show that the composition of the composite hydroxide 1 is Ni: Co: Mn (molar ratio (% of atomic number)) = Ni: Co: Mn = 0.60: 0.20: 0.20). This is an example of satisfying.

As shown in FIGS. 5 and 6, even when the composition of the composite hydroxide 1 is different, the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power are adjusted in the same manner as in the above-mentioned examples of FIGS. 3 and 4. Therefore, the morphology (shape) of the primary particles 2 and the secondary particles 3 can be controlled, and the sparse density and the particle size d of the secondary particles 3 can be precisely controlled in a wider range.

As described above, when the inside of the secondary particles 3 has a dense structure while maintaining the particle size of the composite hydroxide 1, the dissolved oxygen concentration is lowered, the dissolved nickel concentration is increased, and the stirring power is increased. It is preferable to adjust so as to increase, and when the inside of the secondary particle 3 has a sparse structure, it is preferable to increase the dissolved oxygen concentration, decrease the dissolved nickel concentration, and adjust so as to decrease the stirring power. ..

In the above example, only the case where the dissolved nickel concentration and the stirring power are adjusted to be increased or decreased according to the increase or decrease of the dissolved oxygen concentration is described, but other adjustments can be made. For example, it is also possible to adjust the dissolved oxygen concentration so that the dissolved nickel concentration and / or the stirring power becomes constant with respect to the increase or decrease. In such a case, the range in which a constant particle size can be maintained becomes narrow, and the average particle size fluctuates with the sparse density. Therefore, in order to obtain the desired average particle size and sparse density, the relationship between these factors (parameters) and the average particle size and sparse density is measured in advance, and each factor (parameter) is adjusted according to the measurement result. It is preferable to do so.

Further, the average particle size of the composite hydroxide can be controlled by adjusting the dissolved oxygen concentration, the dissolved nickel concentration and the stirring power, particularly the dissolved nickel concentration and the stirring power, as described above, but other known ones. The average particle size may be controlled by combining the above methods. As another control method of the average particle size, a general method for controlling the particle size when obtaining a composite hydroxide by crystallization can be used. For example, in the batch-type crystallization method, the average particle size can be controlled by adjusting the total supply amount of the metal salt as a raw material, so that the total supply amount of the metal salt and each of the above factors are combined. Therefore, the average particle size may be controlled more efficiently. Further, for example, in the continuous crystallization method, the average particle size can be controlled by adjusting the residence time in the tank. Therefore, by combining this residence time with the above factors, the average particle size can be controlled more efficiently. Can be controlled.

Hereinafter, specific aspects of the conditions in the manufacturing method of the present embodiment will be described.

(Dissolved oxygen concentration)
The dissolved oxygen concentration in the reaction aqueous solution can be appropriately adjusted, for example, in the range of 0.2 mg / L or more and 8.5 mg / L or less. By controlling the dissolved oxygen concentration in the above range, the sparse density of the secondary particles 3 can be controlled in a desired range to obtain a composite hydroxide suitable as a precursor of the positive electrode active material. Further, during the crystallization step, it is preferable to control the dissolved oxygen concentration so as to be within a certain range. The fluctuation range of the dissolved oxygen concentration is preferably, for example, within ± 0.2 mg / L, and more preferably within ± 0.1 mg / L.

The dissolved oxygen concentration can be measured by a method such as a winkler method (chemical analysis method), a diaphragm permeation method (electrochemical measurement method), or a fluorescence measurement method. Further, as the method for measuring the dissolved oxygen concentration, any of the above-mentioned methods may be used because the same measured value of the dissolved oxygen concentration can be obtained by using any of the above-mentioned methods. The concentration of dissolved oxygen in the reaction aqueous solution is controlled by introducing a gas such as an inert gas (for example, _N2 gas or Ar gas), air, or oxygen into the reaction vessel to control the flow rate and composition of these gases. It can be adjusted by doing. These gases may be flown into the space inside the reaction vessel or may be blown into the reaction aqueous solution. Further, by appropriately stirring the reaction aqueous solution with a power within the range described later using a stirring device such as a stirring blade, the dissolved oxygen concentration of the entire reaction aqueous solution can be made more uniform.

When the obtained composite hydroxide 1 is used as a precursor of a positive electrode active material, the dissolved oxygen concentration is preferably adjusted in the range of 0.5 mg / L or more and 8.0 mg / Lmg / L or less. When the dissolved oxygen concentration is in the above range, it is easy to control the average sparse density in a range suitable as a precursor of the positive electrode active material (for example, in the range of 0.5% or more and 40% or less). When the dissolved oxygen concentration is lower than 0.5 mg / L, the oxidation of transition metals, especially manganese, hardly proceeds, and as a result, the inside of the secondary particles 3 becomes extremely dense and the surface shows a specific shape. I have something to do. The positive electrode active material obtained by using such a composite hydroxide may have a high reaction resistance and a decrease in output characteristics. On the other hand, when the dissolved oxygen concentration exceeds 8.0 mg / L, the generated secondary particles become extremely sparse, and the shape of the secondary particles 3 also collapses significantly, so that the particle filling property may be significantly deteriorated. The positive electrode active material obtained by using such a composite hydroxide has low output characteristics and may have a low energy density in terms of filling property.

Further, for example, when the target of the obtained average particle size is fixed and the composite hydroxide 1 is produced by crystallization, a precursor of a positive electrode active material (composite hydroxide 1) capable of increasing the output of a battery is used. From the viewpoint of obtaining, the dissolved oxygen concentration is preferably in the range of 5.5 mg / L or more and 8.0 mg / L or less. When the dissolved oxygen concentration is in the above range, for example, a composite hydroxide 1 having a high average sparse density as shown in FIGS. 3E to 3H is obtained, and a positive electrode produced using this composite hydroxide 1 is obtained. Since the active material has a high specific surface area, it has high output characteristics.

Further, from the viewpoint of obtaining a precursor (composite hydroxide 1) that can be used as a positive electrode active material with an emphasis on the balance between the capacity and output characteristics of the battery, the dissolved oxygen concentration is 3.5 mg / L or more. It is preferable to adjust to a range of less than 5 mg / L. When the dissolved oxygen concentration is in the above range, for example, as shown in FIGS. 3C and 3D, the composite hydroxide 1 having an appropriate sparse density and an excellent balance between the specific surface area and the filling density (tap density). Therefore, the positive electrode active material produced by using this composite hydroxide 1 has an excellent balance between the output characteristics and the capacity of the secondary battery.

Further, the dissolved oxygen concentration is adjusted to a range of 0.5 mg / L or more and less than 3.5 mg / L from the viewpoint of obtaining a precursor (composite hydroxide 1) of a positive electrode active material capable of increasing the capacity of the battery. It is preferable to do so. When the dissolved oxygen concentration is in this range, for example, as shown in FIGS. 3A and 3B, the composite hydroxide 1 having a dense structure and a high filling density (tap density) can be obtained. , The positive electrode active material produced by using this composite hydroxide 1 has a high filling density, and therefore has a high secondary battery capacity.

As described above, by adjusting the dissolved oxygen concentration to an appropriate range and controlling the sparse density of the obtained composite hydroxide 1, various properties required for the positive electrode active material can be easily realized. A possible precursor (composite hydroxide 1) can be easily obtained. Further, the dissolved oxygen concentration is preferably adjusted based on a relationship having a positive correlation with the average sparse density, as shown in FIGS. 4A, B and 6A, B. The dissolved oxygen concentration and the average sparse density can have a high positive correlation as a correlation coefficient of 0.7 or more, preferably 0.8 or more. When the correlation coefficient is within the above range, the average sparse density can be controlled more precisely and easily by adjusting the dissolved oxygen concentration. The correlation coefficient can be set in the above range, for example, by appropriately adjusting the dissolved nickel concentration corresponding to the dissolved oxygen concentration.

(Dissolved nickel concentration)
The concentration of dissolved nickel in the reaction aqueous solution can be adjusted in the range of 10 mg / L or more and 1500 mg / L or less based on the temperature of the reaction aqueous solution, and can be adjusted in the range of 10 mg / L or more and 1200 mg / L or less. preferable. By appropriately adjusting the dissolved nickel concentration in the above range, the particle size and sparse density can be controlled in a desired range, and the nickel-manganese composite having a particle morphology suitable as a precursor of a positive electrode active material and high spheroidity can be controlled. Hydroxides can be easily obtained. When the concentration of dissolved nickel in the reaction aqueous solution is lower than 10 mg / L, the growth rate of the primary particles is high and nucleation is more likely to occur than the particle growth, so that the primary particles 2 become too fine, have a small particle size, and are spherical. It tends to be a bad secondary particle. Since such secondary particles have extremely low filling properties, a high energy density may not be obtained when a positive electrode active material obtained from a composite hydroxide is used in a battery. On the other hand, when the dissolved nickel concentration exceeds 1500 mg / L, the formation rate of the composite hydroxide 1 (secondary particles 3) becomes significantly slow, nickel remains in the filtrate, and the composition of the obtained composite hydroxide 1 becomes It may deviate significantly from the target value. Further, under the condition that the dissolved nickel concentration is too high, the amount of impurities contained in the composite hydroxide 1 becomes remarkably large, and the battery characteristics when the positive electrode active material obtained from the composite hydroxide is used for the battery are deteriorated. May cause you to. Further, during the crystallization step, it is preferable to control the dissolved nickel concentration so as to be within a certain range. The fluctuation range of the dissolved nickel concentration can be, for example, within ± 20 mg / L. The dissolved nickel concentration can be measured, for example, by chemically analyzing the amount of Ni in the liquid component of the reaction aqueous solution by ICP emission spectroscopy.

Further, for example, when the dissolved nickel concentration is adjusted in the range of 400 mg / L or more and 1500 mg / L or less, by optimizing other conditions, the sparse density of the secondary particles 3 can be controlled and the primary particles 2 can be controlled. The arrangement (crystal orientation) can be controlled to obtain, for example, a nickel-manganese composite hydroxide having a radial structure. The dissolved nickel concentration can be controlled by controlling the temperature of the reaction aqueous solution and the atmosphere in the reaction vessel within a certain range, and then adjusting the pH value of the reaction solution and the concentration of a complexing agent, for example, ammonium ion. can.

Further, as shown in FIGS. 4A and 4C and FIGS. 6A and 6C, the particle size of the secondary particles 3 is constant by adjusting the dissolved nickel concentration based on the relationship having a negative correlation with the sparse density. It is possible to control the sparse density in a wide range while maintaining. The correlation coefficient between the dissolved nickel concentration and the sparse density is, for example, −0.7 or less, preferably −0.8 or less. When the correlation coefficient is within the above range, the particle size and sparse density can be controlled more accurately and easily.

(Stirring power)
The stirring power applied to the reaction aqueous solution can be adjusted in the range of 0.5 kW / m ³ or more and 15 kW / m ³ or less, and can be adjusted in the range of 2 kW / m ³ or more and 14 kW / m ³ or less. It is preferable that the range is 3 kW / m ³ or more and 12 kW / m ³ or less. By setting the stirring power within the above range, it is possible to suppress excessive miniaturization and coarsening of the secondary particles, and to make the particle size of the composite hydroxide 1 more suitable as the positive electrode active material. Further, when the stirring power is less than 0.5 kW / m ³ , the primary particles 2 tend to be excessively aggregated, and coarse secondary particles 3 may be formed. Further, if the dissolved oxygen concentration is low and the stirring power is low, the secondary particles 3 tend to be sparse, and the filling property of the obtained positive electrode active material may be lowered. On the other hand, if it exceeds 15 kW / m ³ , the aggregation of the primary particles tends to be excessively suppressed, and the secondary particles 3 may become too small. Further, during the crystallization step, it is preferable to control the stirring power so as to be within a certain range. The fluctuation range of the stirring power can be, for example, within ± 0.2 kW / m ³ . Further, the stirring power may be adjusted in the range of 7 kW / m ³ or less, or may be adjusted in the range of 6.5 kW / m ³ or less, for example. The stirring power is controlled within the above range by adjusting the size, rotation speed, etc. of a stirring device such as a stirring blade provided in the reaction vessel.

Further, as shown in FIGS. 4A and D and FIGS. 6A and 6D, the particle size of the secondary particles 3 is adjusted by adjusting the stirring power based on the relationship having a negative correlation with respect to the sparse density. It is possible to control the density in a wide range while maintaining it. The correlation coefficient between the stirring power and the sparse density is, for example, −0.7 or less, preferably −0.8 or less. When the correlation coefficient is within the above range, the particle size and sparse density can be controlled more accurately and easily.

(Reaction temperature)
The temperature of the reaction aqueous solution in the crystallization reaction tank is preferably in the range of 35 ° C. or higher and 60 ° C. or lower, and more preferably in the range of 38 ° C. or higher and 50 ° C. or lower. When the temperature of the reaction aqueous solution exceeds 60 ° C., the priority of nucleation is higher than that of particle growth in the reaction aqueous solution, and the shape of the primary particles 2 constituting the composite hydroxide 1 tends to be too fine. When such a composite hydroxide 1 is used, there is a problem that the filling property of the obtained positive electrode active material is lowered. On the other hand, when the temperature of the reaction aqueous solution is less than 35 ° C., the particle growth tends to be prioritized over the nucleation in the reaction aqueous solution, so that the primary particles 2 and the secondary particles constituting the composite hydroxide 1 tend to be prioritized. The shape of 3 tends to be coarse. When a composite hydroxide having such coarse secondary particles 3 is used as a precursor of the positive electrode active material, a positive electrode active material containing very large coarse particles that cause irregularities during electrode production is formed. There is a problem. Further, when the reaction aqueous solution is lower than 35 ° C., there is a problem that the residual amount of metal ions in the reaction water solution is high and the reaction efficiency is very poor, and a composite hydroxide containing a large amount of impurity elements is generated. It is easy for problems to occur.

(PH value)
The pH value of the reaction aqueous solution is preferably in the range of 10.0 or more and 13.0 or less based on the liquid temperature of 25 ° C. When the pH value is in the above range, the morphology of the secondary particles 3 is appropriately controlled while controlling the size and shape of the primary particles 2 to control the sparse density within a desired range, and the precursor of the positive electrode active material is controlled. A more suitable composite hydroxide 1 can be obtained as a body. Further, when the pH value is less than 10.0, the production rate of the composite hydroxide 1 becomes significantly slow, nickel remains in the filtrate, and the composition of the obtained composite hydroxide 1 deviates significantly from the target value. There is. On the other hand, when the pH value exceeds 13.0, the growth rate of the particles is high and nucleation is likely to occur, so that the particles tend to have a small particle size and poor sphericalness.

(Other conditions)
The production method of the present embodiment includes a crystallization step of neutralizing a salt containing at least nickel and manganese in the reaction aqueous solution to form nickel-manganese composite hydroxide particles. As a specific embodiment of the crystallization step, for example, a neutralizing agent (for example, an alkaline solution, etc.) is used while stirring a mixed aqueous solution containing at least nickel (Ni) and manganese (Mn) in the reaction vessel at a constant rate. ) Can be added for neutralization to control the pH, and one composite hydroxide particle can be produced by co-precipitation. In the production method of the present embodiment, either a batch method crystallization method or a continuous crystallization method can be adopted. Here, the continuous crystallization method is a crystallization method in which the composite hydroxide particles generated by the overflow are recovered while the neutralizing agent is supplied while the mixed aqueous solution is continuously supplied to control the pH. .. In the continuous crystallization method, particles having a wider particle size distribution can be obtained as compared with the batch method, and particles having a high packing property can be easily obtained. Further, the continuous crystallization method is suitable for mass production and is an industrially advantageous production method. For example, when the above-mentioned composite hydroxide 1 of the present embodiment is produced by a continuous crystallization method, the filling property (tap density) of the obtained composite hydroxide 1 particles can be further improved, which is higher. The composite hydroxide 1 having fillability and sparse density can be easily and mass-produced.

As the mixed aqueous solution, an aqueous solution containing at least nickel and manganese, that is, an aqueous solution in which at least nickel salt and manganese salt are dissolved can be used. Further, the mixed aqueous solution may contain M, or an aqueous solution in which a nickel salt, a manganese salt and a salt containing M are dissolved may be used. As the salt containing nickel salt, manganese salt and M, for example, at least one selected from the group consisting of sulfate, nitrate and chloride can be used. Among these, it is preferable to use sulfate from the viewpoint of cost and waste liquid treatment.

The concentration of the mixed aqueous solution is preferably 1.0 mol / L or more and 2.4 mol / L or less, and more preferably 1.2 mol / L or more and 2.2 mol / L or less in total of the dissolved metal salts. .. If the concentration of the mixed aqueous solution is less than 1.0 mol / L in total of the dissolved metal salts, the concentration is too low, and the primary particles 2 constituting the composite hydroxide 1 (secondary particles 3) may not grow sufficiently. There is. On the other hand, when the concentration of the mixed aqueous solution exceeds 2.4 mol / L, the saturation concentration at room temperature is exceeded, so that there is a risk that crystals will reprecipitate and clog the piping. Further, in this case, the amount of nucleation of the primary particles 2 may increase, and the proportion of fine particles in the obtained composite hydroxide particles may increase. Here, the composition of the metal element contained in the mixed aqueous solution and the composition of the metal element contained in the obtained composite hydroxide 1 are the same. Therefore, the composition of the metal element in the mixed aqueous solution can be adjusted so as to have the same composition as the metal element of the target composite hydroxide 1.

As the neutralizing agent, an alkaline solution can be used, and for example, a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. Among these, it is preferable to use an aqueous sodium hydroxide solution from the viewpoint of cost and ease of handling. Although the alkali metal hydroxide can be added directly to the reaction aqueous solution, it is preferable to add it as an aqueous solution because of the ease of pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 12% by mass or more and 30% by mass or less, and more preferably 20% by mass or more and 30% by mass or less. If the concentration of the aqueous alkali metal hydroxide solution is less than 12% by mass, the amount supplied to the reaction vessel may increase and the particles may not grow sufficiently. On the other hand, when the concentration of the aqueous alkali metal hydroxide solution exceeds 30% by mass, the pH value is locally increased at the position where the alkali metal hydroxide is added, and fine particles may be generated.

Further, the complexing agent can be added to the mixed aqueous solution together with the neutralizing agent. The complexing agent is not particularly limited as long as it can be combined with a metal element such as nickel ion or manganese ion in an aqueous solution to form a complex. For example, as the complexing agent, an ammonium ion feeder may be used. Can be mentioned. The ammonium ion feeder is not particularly limited, and for example, at least one selected from the group consisting of aqueous ammonia, an aqueous solution of ammonium sulfate, and an aqueous solution of ammonium chloride can be used. Among these, it is preferable to use ammonia water because of its ease of handling. When an ammonium ion feeder is used, the concentration of ammonium ions is preferably in the range of 5 g / L or more and 25 g / L or less.

Further, the production method of the present embodiment preferably includes a washing step after the crystallization step. The cleaning step is a step of cleaning impurities contained in the composite hydroxide 1 obtained in the crystallization step with a cleaning solution. It is preferable to use pure water as the cleaning solution. The amount of the washing solution is preferably 1 L or more with respect to 300 g of the composite hydroxide 1, for example. If the amount of the washing solution is less than 1 L with respect to 300 g of the composite hydroxide 1, the washing may be insufficient and impurities may remain in the composite hydroxide 1. As a cleaning method, for example, a cleaning solution such as pure water may be passed through a filter such as a filter press. When it is desired to further wash SO ₄ remaining in the composite hydroxide 1, it is preferable to use sodium hydroxide, sodium carbonate or the like as the washing solution.

(2) Nickel-manganese composite hydroxide 1 Since the composite hydroxide 1 obtained by the production method of the present embodiment can control the average particle size and the sparse density, the composite hydroxide 1 is used as a precursor. The non-aqueous electrolyte secondary battery containing the positive electrode active material used can easily control the balance between capacity and output characteristics. Further, since the composite hydroxide 1 is composed of the secondary particles 3 formed by agglomerating the primary particles 2, it is easy to control the average particle size and the sparse density. The composite hydroxide 1 is mainly composed of secondary particles 3 in which the primary particles 2 are aggregated, but the composite hydroxide obtained in the production method of the present embodiment is, for example, as secondary particles 3. It may contain a small amount of primary particles 2 such as the primary particles 2 that did not aggregate and the primary particles 2 that fell off from the secondary particles 3 after aggregation.

The composite hydroxide 1 is represented by the general formula (1): Ni _x Mn _y M _z (OH) _{2 + α} . In the above formula (1), M is at least one element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W, and x is 0.1. ≦ x ≦ 0.9, y is 0.05 ≦ y ≦ 0.8, z is 0 ≦ z ≦ 0.8, and x + y + z = 1.0 is satisfied, and α is 0 ≦ α ≦ 0. It is 4. Further, when M is Co, it is superior in battery capacity and output characteristics. In the above formula (1), α is a coefficient that changes according to the valence of the metal element contained in the composite hydroxide 1.

In the above formula (1), when y indicating the content of Mn in the composite hydroxide 1 is in the above range, the morphology (shape) of the primary particles 2 depends on the dissolved oxygen concentration in the reaction aqueous solution in the crystallization step. ) Can be adjusted, whereby the sparse density can be controlled within a desired range. Further, from the viewpoint of controlling the sparse density more precisely, y is preferably 0.1 ≦ y ≦ 0.8. Further, when the value of y is 0.2 or more, the sparse density of the secondary particles 3 can be controlled at a lower dissolved oxygen concentration, so that excessive oxidation of the transition metal can be prevented.

The particle size of the composite hydroxide 1 is not particularly limited and may be in a desired range, but when used as a precursor of a positive electrode active material, the volume average particle size (MV) may be 5 μm or more and 20 μm or less. It is more preferably 6 μm or more and 15 μm or less. When the volume average particle size (MV) is less than 5 μm, the filling property of one composite hydroxide particle is greatly lowered, and it is difficult to increase the battery capacity per weight when the positive electrode active material is used. On the other hand, when the volume average particle size (MV) exceeds 20 μm, the filling property does not deteriorate significantly, but the specific surface area decreases, so that the reactivity with the lithium raw material when making the positive electrode active material decreases, and the battery characteristics are high. The positive electrode active material with the above cannot be obtained. In this case, the synthesized positive electrode active material further deteriorates the cycle characteristics and the interface with the electrolytic solution, so that the resistance of the positive electrode increases and the output characteristics of the battery deteriorate. The volume average particle size (MV) can be measured by, for example, a laser diffraction / scattering type particle size distribution measuring device.

The composite hydroxide 1 preferably has an average sparse density of 0.5% or more and 40% or less obtained from the image analysis result of the particle cross-sectional SEM image. When the average sparse density exceeds 40%, the composite hydroxide 1 particles are fragile and easily crumble, so that the filling property of the composite hydroxide 1 and the filling property of the positive electrode active material obtained by using the composite hydroxide 1 are lowered. do. Therefore, a high volumetric energy density cannot be obtained when the positive electrode active material is used. Further, since such a positive electrode active material has a collapsed shape, the contact surface with the conductive auxiliary agent or the like becomes small, and as a result, the resistance also increases and the output characteristics of the battery deteriorate.

The composite hydroxide 1 preferably has a [D90-D10] / volume average particle size, which is an index indicating the spread of the particle size distribution, of 0.7 or more. When [D90-D10) / volume average particle size] is less than 0.7, the uniformity of the particle size becomes high and the battery capacity per weight tends to be high, but the particle filling property is lowered and the volume is reduced. Energy density may be low. [D90-D10) / volume average particle size] is determined by, for example, mixing composite hydroxides 1 having different particle sizes or producing the composite hydroxide 1 by using a continuous crystallization method. It can be adjusted to the above range. In the above [(D90-D10) / volume average particle size], D10 accumulates the number of particles in each particle size from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles. D90 also means a particle size in which the number of particles is accumulated and the accumulated volume is 90% of the total volume of all the particles. Further, the average particle size is a volume average particle size MV, which means an average particle size weighted by volume. The volume average particle size MV and D90 and D10 can be measured by using a laser light diffraction / scattering type particle size analyzer.

The tap density of the composite hydroxide 1 is preferably in the range of 1.0 g / cm ³ or more and 2.5 g / cm ³ or less, and preferably in the range of 1.8 g / cm ³ or more and 2.3 g / cm ³ or less. Is more preferable. When the tap density is in the above range, the filling property of the positive electrode active material using the composite hydroxide 1 as a precursor is excellent, and the battery capacity can be improved.

The specific surface area of the composite hydroxide 1 is preferably in the range of 2.5 m ² / g or more and 50 m ² / g or less, and preferably in the range of 4 m ² / g or more and 15 m ² / g or less. When the specific surface area is in the above range, it is more excellent in the output characteristics of the positive electrode active material using the composite hydroxide 1 as a precursor. The tap density and specific surface area can be set in the above range by adjusting the particle size distribution including the volume average particle size (MV) of the composite hydroxide 1 and the sparse density.

(3) Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery FIG. 7 is a diagram showing an example of a method for producing a positive electrode active material according to the present embodiment. As shown in FIG. 7, the method for producing the positive electrode active material of the present embodiment is described in the general formula (2): Li _{1 + t} Ni _x Mn _y M _z O _{2 + β} (in the formula (2), M is Co, Ti, V. , Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, which are at least one additive element, where t is −0.05 ≦ t ≦ 0.5 and x is 0.1. ≦ x ≦ 0.9, y is 0.05 ≦ y ≦ 0.8, z is 0 ≦ z ≦ 0.8, and x + y + z = 1.0 is satisfied, and β is 0 ≦ β ≦. It is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is represented by (0.5) and contains a lithium nickel-manganese composite oxide composed of secondary particles in which primary particles are aggregated, and is the above-mentioned production method. The present invention comprises a step of mixing the composite hydroxide 1 obtained in the above method and a lithium compound to obtain a mixture, and a firing step of firing the mixture to obtain a lithium nickel-manganese composite oxide. The positive electrode active material obtained by using the above-mentioned composite hydroxide 1 as a precursor can easily control the capacity and output characteristics of the secondary battery using the positive electrode active material, and therefore has extremely high industrial value. Hereinafter, a method for producing a positive electrode active material will be described.

(Mixing process)
First, the above-mentioned composite hydroxide 1 and a lithium compound are mixed to form a mixture. As the lithium compound, a known lithium compound can be used without particular limitation, and for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferably used from the viewpoint of easy availability. .. Among these, as the lithium compound, lithium oxide or lithium carbonate is more preferable from the viewpoint of ease of handling and stability of quality. Before the mixing step, the composite hydroxide 1 may be oxidized to form at least a part of the nickel-manganese composite oxide, and then mixed.

The composite hydroxide 1 and the lithium compound are the sum of the atomic numbers of metals other than lithium in the lithium mixture, that is, the sum of the atomic numbers of nickel, cobalt and additive elements (Me), and the atomic number of lithium (Li). The mixture is mixed so that the ratio (Li / Me) is 0.95 or more and 1.50 or less, preferably 0.95 or more and 1.20 or less. That is, since Li / Me does not change before and after firing, the Li / Me ratio mixed in this mixing step is the Li / Me ratio in the positive electrode active material, so that the Li / Me in the lithium mixture is the positive electrode activity to be obtained. It is mixed so as to be the same as Li / Me in the substance.

Further, a general mixer can be used for mixing, and a shaker mixer, a ladyge mixer, a juria mixer, a V blender, or the like can be used, and it is sufficient that the skeleton of the composite hydroxide 1 is not destroyed. It may be mixed.

(Baking process)
The lithium mixture is then calcined to give a lithium nickel-nickel-manganese composite oxide. Firing is performed, for example, in an oxidizing atmosphere at 700 ° C. or higher and 1100 ° C. or lower. If the firing temperature is less than 700 ° C., firing may not be sufficiently performed and the tap density may decrease. Further, when the firing temperature is less than 700 ° C., the diffusion of lithium does not proceed sufficiently, excess lithium remains, the crystal structure is not arranged, and the composition of nickel, manganese, etc. inside the particles is sufficiently uniform. In some cases, sufficient characteristics may not be obtained when used in a battery. On the other hand, if the temperature exceeds 1100 ° C., the sparse portion of the particle surface may become dense. In addition, intense sintering may occur between the particles of the lithium nickel-manganese composite oxide and abnormal grain growth may occur. Therefore, the particles after firing may become coarse and may not be able to maintain a substantially spherical particle morphology. There is sex. Since such a positive electrode active material has a reduced specific surface area, when used in a battery, there arises a problem that the resistance of the positive electrode increases and the battery capacity decreases. The firing time is not particularly limited, but is about 1 hour or more and 24 hours or less.

From the viewpoint of uniformly reacting the composite hydroxide 1 or the nickel-manganese composite oxide obtained by oxidizing the composite hydroxide with the lithium compound, the temperature rising rate is, for example, 1 ° C./min or more and 10 ° C. It is preferable to raise the temperature to the above-mentioned firing temperature in the range of / min or less. Further, by holding the lithium compound at a temperature near the melting point for about 1 hour to 10 hours before firing, the reaction can be carried out more uniformly.

In the method for producing the positive electrode active material of the present embodiment, the composite oxide used did not aggregate as the secondary particles 3 other than the composite hydroxide 1 composed of the secondary particles 3 in which the primary particles 2 aggregated. It may contain a single primary particle 2 such as a primary particle 2 or a primary particle 2 that has fallen off from the secondary particle 3 after aggregation. Further, the composite oxide used may contain a composite hydroxide produced by a method other than the above, or a composite oxide obtained by oxidizing the composite hydroxide, as long as the effect of the present invention is not impaired. The positive electrode active material obtained is mainly composed of lithium nickel-manganese composite oxide composed of secondary particles in which primary particles are aggregated, but primary particles that are not aggregated as secondary particles and secondary particles after aggregation. It may contain a single primary particle such as a primary particle shed from.

Specific examples of the present invention will be described below. However, the present invention is not limited to these examples.

(Example 1)
[Preparation of composite hydroxide]
A predetermined amount of pure water was put into the reaction tank (60 L), and the stirring power was adjusted to 6.0 kW / m ³ . Next, the temperature (liquid temperature) in the reaction vessel was set to 45 ° C. while stirring. At this time, nitrogen gas (N ₂ ) was supplied into the reaction vessel, and the N ₂ flow rate was adjusted so that the dissolved oxygen concentration in the reaction vessel liquid became 2.8 mg / L. A mixed aqueous solution of 2.0 mol / L in which nickel sulfate, cobalt sulfate and manganese sulfate are dissolved so that the molar ratio of nickel: cobalt: manganese is 35:35:30 in this reaction vessel, and 25 mass of an alkaline solution. % Sodium hydroxide aqueous solution and 25 mass% ammonia water as a complexing agent were continuously added to the reaction vessel at the same time to form a reaction aqueous solution, and a neutralization crystallization reaction was carried out. The pH value and the ammonium ion concentration were adjusted so that the dissolved nickel concentration was constant at 1080 mg / L. At this time, the ammonium ion concentration in the reaction vessel was in the range of 12 to 15 g / L. Further, the total flow rate of the mixed solution, the sodium hydroxide aqueous solution and the ammonia water was controlled so that the residence time of the metal salt contained in the mixed aqueous solution was 8 hours. After the reaction vessel became stable, the slurry containing the nickel-manganese composite hydroxide was recovered from the overflow port, and then suction filtration was performed to obtain a nickel-manganese composite hydroxide cake. After filtration, impurities were washed by suction filtration while supplying 1 L of pure water to 140 g of the nickel-cobalt-manganese composite hydroxide cake in the filter. Further, the washed nickel-manganese composite hydroxide cake was air-dried at 120 ° C. to obtain a nickel-manganese composite hydroxide.

The particle size distribution of the obtained nickel-cobalt-manganese composite hydroxide was measured using a laser diffraction / scattering type particle size distribution measuring device. As a result, the volume average particle size MV was 10.1 μm, and [(D90-D10) / volume average particle size] was 0.86. The tap density was measured using a tapping device (KYT3000 manufactured by Seishin Corporation), and after tapping 500 times, it was calculated from the volume and the sample weight. As a result, the tap density was 2.12 g / cm ³ . The specific surface area was measured by the BET method by nitrogen adsorption.

The surface and cross-sectional structure of the obtained nickel-cobalt-manganese composite hydroxide were observed with a scanning electron microscope. 3A and 3B show the surface (FIG. 3A) and the cross-sectional structure (FIG. 3B) of the obtained nickel-manganese composite hydroxide. From the results of surface observation, it was confirmed that highly spherical secondary particles composed of plate-shaped primary particles were obtained. From the results of cross-sectional observation, it was confirmed that the inside of the particles had a very dense structure. In addition, in order to evaluate the sparse density, the particle cross-sectional area and the void area inside the particle were obtained using image analysis software (WinLoof 6.1.1), and [(void area inside the particle) / (particle cross-sectional area) ×. The sparse density was calculated from the formula of 100] (%). Twenty cross sections of secondary particles having a volume average particle size (MV) of 80% or more are randomly selected, the sparse densities of the cross sections of these secondary particles are measured, and the average value (average sparse density) is measured. ) Was calculated, and the sparse density was 1.8%.

The obtained nickel-manganese composite hydroxide was dissolved with an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was Ni _0.35 Co _0.35 Mn _0.30 (OH) ₂ . , It was confirmed that the particles having the desired composition were obtained. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1.

(Example 2)
The stirring power in the crystallization step was adjusted to 5.8 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction vessel was 970 mg / L and the dissolved oxygen concentration was 4.5 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except for the above. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. 3C and 3D show the surface (FIG. 3C) and cross-sectional structure (FIG. 3D) of the obtained nickel-manganese composite hydroxide. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 3)
The stirring power in the crystallization step was adjusted to 5.5 kW / m ³ , and the dissolved nickel concentration in the reaction aqueous solution was changed to 410 mg / L, and the dissolved oxygen concentration was changed to N ₂ so that the dissolved oxygen concentration was 5.8 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except that the mixed gas with ₂ was supplied and the flow rate and pH value were adjusted. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. 3E and F show the surface (FIG. 3E) and cross-sectional structure (FIG. 3F) of the obtained nickel-manganese composite hydroxide. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 4)
The stirring power in the crystallization step was adjusted to 5.2 kW / m ³ , and air was supplied in place of N ₂ so that the concentration of dissolved nickel in the reaction aqueous solution was 300 mg / L and the concentration of dissolved oxygen was 6.2 mg / L. Then, a nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except that the flow rate and the pH value were adjusted. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. 3G and H show the surface (FIG. 3G) and cross-sectional structure (FIG. 3H) of the obtained nickel-manganese composite hydroxide. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 5)
The stirring power in the crystallization step was adjusted to 6.0 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction aqueous solution was 1080 mg / L and the dissolved oxygen concentration was 0.3 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except for the above. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 6)
The stirring power in the crystallization step was adjusted to 5.2 kW / m ³ , and air was supplied in place of N ₂ so that the concentration of dissolved nickel in the reaction aqueous solution was 200 mg / L and the concentration of dissolved oxygen was 8.5 mg / L. Then, a nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except that the flow rate and the pH value were adjusted. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 7)
The stirring power in the crystallization step was adjusted to 5.8 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction aqueous solution was 1700 mg / L and the dissolved oxygen concentration was 3.0 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except for the above. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 8)
The stirring power in the crystallization step was adjusted to 5.8 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction aqueous solution was 8 mg / L and the dissolved oxygen concentration was 0.3 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except for the above. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 9)
The stirring power in the crystallization step was adjusted to 1.8 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction aqueous solution was 970 mg / L and the dissolved oxygen concentration was 4.5 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except for the above. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 10)
The stirring power in the crystallization step was adjusted to 7.2 kW / m ³ , and air was supplied in place of N ₂ so that the concentration of dissolved nickel in the reaction aqueous solution was 300 mg / L and the concentration of dissolved oxygen was 6.2 mg / L. Then, a nickel-manganese composite hydroxide was prepared in the same manner as in Example 1 except that the flow rate and the pH value were adjusted. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 11)
[Preparation of composite hydroxide]
A predetermined amount of pure water was put into the reaction tank (60 L), and the stirring power was adjusted to 6.0 kW / m ³ . Next, the temperature (liquid temperature) in the reaction vessel was set to 45 ° C. while stirring. At this time, nitrogen gas (N ₂ ) was supplied into the reaction vessel, and the N ₂ flow rate was adjusted so that the dissolved oxygen concentration in the reaction vessel liquid became 3.5 mg / L. A mixed aqueous solution of 2.0 mol / L in which nickel sulfate, cobalt sulfate and manganese sulfate are dissolved so that the molar ratio of nickel: cobalt: manganese is 60:20:20 in this reaction vessel, and 25 mass of an alkaline solution. % Sodium hydroxide aqueous solution and 25 mass% ammonia water as a complexing agent were continuously added to the reaction vessel at the same time to form a reaction aqueous solution, and a neutralization crystallization reaction was carried out. The pH value and the ammonium ion concentration were adjusted so that the dissolved nickel concentration was constant at 720 mg / L. At this time, the ammonium ion concentration in the reaction vessel was in the range of 12 to 15 g / L. Further, the total flow rate of the mixed solution, the sodium hydroxide aqueous solution and the ammonia water was controlled so that the residence time of the metal salt contained in the mixed aqueous solution was 8 hours. After the reaction vessel became stable, the slurry containing the nickel-manganese composite hydroxide was recovered from the overflow port, and then suction filtration was performed to obtain a nickel-manganese composite hydroxide cake. After filtration, impurities were washed by suction filtration while supplying 1 L of pure water to 140 g of the nickel-cobalt-manganese composite hydroxide cake in the filter. Further, the washed nickel-manganese composite hydroxide cake was air-dried at 120 ° C. to obtain a nickel-manganese composite hydroxide. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. 5I and J show the surface (FIG. 5I) and cross-sectional structure (FIG. 5H) of the obtained nickel-manganese composite hydroxide. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 12)
The stirring power in the crystallization step was adjusted to 5.8 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction vessel was 350 mg / L and the dissolved oxygen concentration was 5.8 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 11. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. 5K and L show the surface (FIG. 5K) and cross-sectional structure (FIG. 5L) of the obtained nickel-manganese composite hydroxide. In addition, each evaluation was performed in the same manner as in Example 1.

(Example 13)
The stirring power in the crystallization step was adjusted to 5.5 kW / m ³ , and the N ₂ flow rate and pH value were adjusted so that the dissolved nickel concentration in the reaction vessel was 150 mg / L and the dissolved oxygen concentration was 7.8 mg / L. A nickel-manganese composite hydroxide was prepared in the same manner as in Example 11. The characteristics of the obtained nickel-manganese composite hydroxide are shown in Table 1. 5M and N show the surface (FIG. 5M) and cross-sectional structure (FIG. 5N) of the obtained nickel-manganese composite hydroxide. In addition, each evaluation was performed in the same manner as in Example 1.

(evaluation)
In Examples 1 to 13, the average particle size and the average sparse density in various ranges are controlled by adjusting the dissolved oxygen concentration, the dissolved nickel concentration, and the stirring power. Examples 1 to 7 (Ni: Co: Mn = 0.35: 0.35: 0.30) and Examples 11 to 13 (Ni: Co: Mn = 0.60: 0.20: 0.20). Has various average sparse densities by controlling to have substantially the same average particle size MV and adjusting the dissolved oxygen concentration, the dissolved nickel concentration and the stirring power. From Table 1, it is shown that physical properties such as tap density and specific surface area can be controlled by controlling the sparse density while keeping the volume average particle size constant.

From the above, by combining the dissolved nickel concentration, the dissolved oxygen concentration, and the stirring power, the powder characteristics and sparse density of the composite hydroxide 1 can be widely controlled, and the balance between the capacity and output characteristics of the obtained positive electrode active material can be precisely balanced. It becomes possible to control. Further, based on these measurement results, the average particle size and sparse density of the secondary particles can be controlled more precisely and easily within a desired range.

1 ... Nickel-manganese composite hydroxide 2 ... Primary particles 3 ... Secondary particles 4 ... Voids in the secondary particles d ... Particle size of the secondary particles

Claims (7)

General formula (1): Ni _x Mn _y M _z (OH) _{2 + α} (In the above formula (1), M is selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, W. At least one kind of additive element to be added, x is 0.1 ≦ x ≦ 0.9, y is 0.05 ≦ y ≦ 0.8, and z is 0 ≦ z ≦ 0.8. , And x + y + z = 1.0, α is represented by 0 ≦ α ≦ 0.4), and a nickel-manganese composite hydroxide composed of secondary particles in which a plurality of primary particles are aggregated. It ’s a manufacturing method,
It comprises a crystallization step of neutralizing salts containing at least nickel and manganese in the reaction aqueous solution to form a nickel-manganese composite hydroxide.
The crystallization step includes a step of continuously adding a mixed aqueous solution containing nickel and manganese to the reaction vessel to neutralize and overflow the slurry containing the nickel-manganese composite hydroxide particles to recover the particles. ,
In the crystallization step,
For the sparse density represented by [(void area inside the secondary particle / cross-sectional area of the secondary particle) × 100] (%) at an arbitrary volume average particle size of the nickel-manganese composite hydroxide , the above Based on the relationship that the dissolved oxygen concentration in the reaction aqueous solution has a positive correlation, and the dissolved nickel concentration in the reaction aqueous solution and the stirring power loaded on the reaction aqueous solution each have a negative phase.
The dissolved oxygen concentration in the reaction aqueous solution is within the range of 0.2 mg / L or more and 8.0 mg / L or less, and the fluctuation range is within the range of ± 0.2 mg / L.
The concentration of dissolved nickel in the reaction aqueous solution is within the range of 10 mg / L or more and 1500 mg / L or less, and
By adjusting the stirring power applied to the reaction aqueous solution within the range of 0.5 kW / m ³ or more and 15 kW / m ³ or less,
The volume average particle size is controlled within a range of 5 μm or more and 20 μm or less, and the sparse density is controlled within a range of 0.5% or more and 40% or less, respectively.
A method for producing a nickel-manganese composite hydroxide. The method for producing a nickel-manganese composite hydroxide according to claim 1, wherein the sparse density is controlled by adjusting at least the dissolved oxygen concentration and the dissolved nickel concentration. The method for producing a nickel-manganese composite hydroxide according to claim 1 or 2, wherein the volume average particle size is controlled by adjusting at least the dissolved nickel concentration and the stirring power. The method for producing a nickel-manganese composite hydroxide according to any one of claims 1 to 3, wherein the temperature of the reaction aqueous solution is in the range of 35 ° C. or higher and 60 ° C. or lower in the crystallization step. The invention according to any one of claims 1 to 4, wherein in the crystallization step, the pH value measured based on the liquid temperature of the reaction aqueous solution at 25 ° C. is in the range of 10.0 or more and 13.0 or less. A method for producing a nickel-manganese composite hydroxide. The nickel-manganese composite according to claim 1, wherein [(D90-D10) / volume average particle size], which is an index showing the spread of the particle size distribution of the nickel-manganese composite hydroxide, is 0.7 or more. Method for producing hydroxide. General formula (2): Li _{1 + t} Ni _x Mn _y M _z O _{2 + β} (In formula (2), M is selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, W. At least one kind of additive element, t is −0.05 ≦ t ≦ 0.5, x is 0.1 ≦ x ≦ 0.9, and y is 0.05 ≦ y ≦ 0. 8.8, z is 0 ≦ z ≦ 0.8, x + y + z = 1.0 is satisfied, and β is 0 ≦ β ≦ 0.5), and the primary particles are aggregated. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium nickel-manganese composite oxide composed of secondary particles.
A step of mixing a nickel-manganese composite hydroxide obtained by the production method according to any one of claims 1 to 6 and a lithium compound to obtain a mixture, and a step of calcining the mixture to obtain lithium nickel. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a step of obtaining a manganese composite oxide.

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