JP6895105B2 - A method for producing nickel-manganese composite hydroxide particles 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 nickel-manganese composite hydroxide particles 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, the development of a small and lightweight non-aqueous electrolyte secondary battery having a high energy density has been strongly desired. Further, it is strongly desired to develop a high output secondary battery as a battery for a power source for driving a motor, particularly a power source for transportation equipment.

As a secondary battery satisfying such a requirement, there is a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery. The non-aqueous electrolyte secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material for the negative electrode and the positive electrode.

Currently, research and development are being actively carried out on non-aqueous electrolyte secondary batteries. Among them, non-aqueous electrolyte secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode material are used. Since a high voltage of 4V class can be obtained, it is being put into practical use as a battery having a high energy density.

As such non-aqueous electrolyte secondary batteries, lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium transition metal composite oxide (LiNiO2) using nickel, which is cheaper than cobalt, and lithium nickel cobalt manganese are currently used. Lithium composite oxides such as composite oxides (LiNi1 / 3Co1 / 3Mn1 / 3O2), lithium manganese composite oxides using manganese (LiMn2O4), and lithium nickel manganese composite oxides (LiNi0.5Mn0.5O2) are used as positive electrode active materials. The lithium ion secondary battery used has been proposed.

Among the positive electrode active materials used in non-aqueous electrolyte secondary batteries, in recent years, the amount of cobalt, which has a small reserve, can be reduced, and the lithium transition metal composite oxide (LiNiO ₂ ), which has a high capacity, and further thermal stability. _{Lithium-nickel-cobalt-manganese composite oxide (LiNi 0.5} Mn _0.5 O ₂ ), which is also excellent, and _{lithium-nickel cobalt-manganese composite oxide (LiNi 1/3} Co), which has better cycle characteristics and high output with low resistance. _1/3 Mn _1/3 O ₂ ) is drawing attention. Examples of technical documents relating to active materials of non-aqueous electrolyte secondary batteries include Patent Documents 1 to 6.

Japanese Unexamined Patent Publication No. 8-321300 Japanese Unexamined Patent Publication No. 10-74516 Japanese Unexamined Patent Publication No. 10-83816 Japanese Unexamined Patent Publication No. 10-74517 Japanese Unexamined Patent Publication No. 2011-119092 Japanese Unexamined Patent Publication No. 2012-246199

By the way, some applications of lithium ion secondary batteries are expected to be used in a mode in which discharge at a high rate (rapid discharge) is repeated. A lithium ion secondary battery used as a vehicle power source, for example, a lithium secondary battery mounted on a hybrid vehicle in which a lithium ion secondary battery is used as a power source and another power source having a different operating principle such as an internal combustion engine is used in combination. The secondary ion battery is a typical example of a lithium ion secondary battery that is expected to be used in this way. However, even though a conventional general lithium-ion secondary battery exhibits relatively high durability for a low-rate charge / discharge cycle, it has an internal resistance for a charge / discharge cycle accompanied by a high-rate discharge. It was easy to cause performance deterioration such as an increase in the battery.

In order to improve the performance deterioration in such high-rate discharge, for example, Patent Document 1 describes a technique in which the positive electrode or the negative electrode of a lithium secondary battery is made of an active material having a porous hollow structure. According to the active material having such a porous hollow structure, the contact area with the electrolytic solution becomes large, the movement of lithium ions becomes easy, and the strain due to the volume expansion of the active material due to the insertion of lithium is suppressed. It is said that a lithium battery with high capacity and long life can be obtained by quick charging.

Further, in Patent Documents 2 to 4, composite oxide particles (lithium cobalt composite oxide particles or spinel type) which are hollow spherical secondary particles in which primary particles are aggregated and have a large number of gaps leading to the inside on the surface thereof. It is described that the utilization rate of the positive electrode active material can be improved by increasing the contact area with the non-aqueous electrolytic solution by using the lithium manganese composite oxide particles) as the positive electrode active material.

Patent Document 5 describes a hollow structure having a secondary particle in which a plurality of primary particles of a lithium transition metal oxide are aggregated and a hollow portion formed inside the secondary particle, thereby exhibiting performance suitable for high output and charging / discharging. It is described that active material particles with less deterioration due to the cycle can be obtained.

Further, Patent Document 6 describes a nucleation step in which nucleation is performed in an oxidizing atmosphere and a particle growth aqueous solution containing nuclei formed in the nucleation step having a pH value of 10 based on a liquid temperature of 25 ° C. By controlling the particle to be lower than the nucleation stage in the range of 5 to 12.0, and by switching from an oxidizing atmosphere to a mixed atmosphere of oxygen and an inert gas having an oxygen concentration of 1% by volume or less in the middle of the particle growth process. A precursor having a hollow structure and an active material obtained by calcining the precursor have been proposed.

However, the conventional active material has a low oil absorption amount, and when used as a positive electrode of a battery, the amount of the electrolytic solution contained in the active material is not sufficient, and a satisfactory output characteristic, particularly in high-rate discharge, can be obtained. There was a problem that there was no. Therefore, in order to improve the output characteristics, a positive electrode active material having a higher oil absorption amount has been required.

In view of the above-mentioned problems, the present invention provides a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which has a high oil absorption and can improve output characteristics when used in a non-aqueous electrolyte secondary battery. An object of the present invention is to provide a method for producing nickel-manganese composite hydroxide particles used as a precursor of the positive electrode active material.

As a result of diligent studies on a lithium transition metal composite oxide capable of exhibiting excellent output characteristics when used as a positive electrode active material for a non-aqueous electrolyte secondary battery, the present inventor performs nucleation based on the pH value of the reaction solution. In the production method of obtaining a precursor of the positive electrode active material by separating the nucleation step and the particle growth step for growing the nuclei, the density of seed particles formed by the initial stage of the nucleation step and the particle growth step is controlled. It was found that the positive electrode active material produced by using the precursor has a high oil absorption and the output characteristics when used in a non-aqueous electrolyte secondary battery are improved. The present invention was completed.

In other words, the general formula of the present _{invention: Ni x Mn y Co z M} t (OH) 2 + α (x + y + z + t = 1,0.3 ≦ x ≦ 0.7,0.1 ≦ y ≦ 0.55,0 ≦ z ≦ 0 .4, 0 ≦ t ≦ 0.1, 0 ≦ α ≦ 0.5, M is an additive element and is selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W 1 A method for producing nickel-cobalt-manganese composite hydroxide particles, which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery represented by (additional elements of more than one species).
The nucleation aqueous solution containing at least a metal compound containing nickel and a metal compound containing manganese and an ammonium ion feeder is controlled so that the pH value becomes 12.0 to 14.0 based on a liquid temperature of 25 ° C. A nucleation step in which nucleation is performed in an oxidizing atmosphere with an oxygen concentration of more than 1% by volume.
A metal compound containing at least nickel, a metal compound containing manganese, and an ammonium ion feeder are supplied to the aqueous solution for particle growth containing nuclei formed in the nucleation step, and the pH value at a liquid temperature of 25 ° C. is adjusted. A seed particle generation step in which seed particles are generated by controlling the pH value to be 10.5 to 12.0 and lower than the pH value in the nucleus generation step.
A metal compound containing at least nickel, a metal compound containing manganese, and an ammonium ion feeder are supplied to the particle growth slurry containing the seed particles formed in the seed particle generation step, and oxygen is generated from the oxidizing atmosphere. It is provided with a particle growth step of switching to a non-oxidizing atmosphere having a concentration of 1% by volume or less and growing the seed particles.
The centrifugal sedimentation density of the seed particles obtained by dividing the solid content density (g / L) of the slurry ^{by the centrifuge sedimentation volume (cm 3} / L) of the slurry is controlled to ^{0.39 g / cm 3 or less.} It is characterized by that.

The time of the seed particle generation step is preferably 40% or less of the total time of the seed particle generation step and the particle growth step.

The oxygen concentration in the oxidizing atmosphere is preferably 10% by volume or more, and the oxygen concentration in the non-oxidizing atmosphere is preferably 0.5% by volume or less.

The method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is described in the general formula: Li _{1 + u} Ni _x Mn _y Co _z M _t O _{2 + α} (−0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0). .3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is an additive element, and Al, Ti, V, Cr, Positive electrode activity for non-aqueous electrolyte secondary batteries represented by one or more elements selected from Zr, Nb, Mo, and W) and composed of a lithium nickel-manganese composite oxide having a hexagonal crystal structure having a layered structure. It ’s a method of manufacturing substances.
A mixing step of mixing nickel-manganese composite hydroxide particles obtained by the above production method and a lithium compound to form a lithium mixture, and a firing step of firing the mixture formed in the mixing step in an oxidizing atmosphere. It is characterized by having and.

In the mixing step, it is preferable to adjust the ratio of the sum of the atomic numbers of the metals other than lithium contained in the lithium mixture to the atomic number of lithium to 0.95 to 1.5.

In the firing step, it is preferable to fire at a temperature of 800 ° C. to 1000 ° C., and in the firing step, it is preferable to perform calcining in advance at a temperature of 350 ° C. to 800 ° C. and a temperature lower than the firing temperature. ..

The positive electrode active material for a non-aqueous electrolyte secondary battery produced by using the nickel-manganese composite hydroxide particles obtained by the present invention as a precursor has a high oil absorption and can improve the output characteristics when used in a battery. And its industrial value is extremely large.

FIG. 1 is a schematic flowchart of a process for producing nickel-manganese composite hydroxide particles of the present invention. FIG. 2 is a schematic flowchart of a process for producing a lithium nickel-manganese composite oxide which is a positive electrode active material from the nickel-manganese composite hydroxide particles of the present invention.

The present invention relates to a method for producing nickel-manganese composite hydroxide particles and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. In order to improve the performance of a non-aqueous electrolyte secondary battery (hereinafter, may be referred to as a "secondary battery" or "battery"), a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, may be referred to as a "battery") is used. Hereinafter, it may be referred to as “positive electrode active material”). In order to obtain a secondary battery having excellent output characteristics, a positive electrode active material having a high oil absorption is required. Each of the present inventions will be described in detail below. First, a method for producing nickel-manganese composite hydroxide particles, which is the greatest feature of the present invention, will be described.

(1) The method of producing a nickel-manganese composite hydroxide particles of the manufacturing method of the present invention a nickel-manganese composite hydroxide particles represented by the general _{formula: Ni x Mn y Co z M} t (OH) 2 + α (x + y + z + t = 1,0. 3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ α ≦ 0.5, M is an additive element, and Al , Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), nickel cobalt, which is a precursor of the positive electrode active material for non-aqueous electrolyte secondary batteries. A method for producing manganese composite hydroxide particles.
The nucleation aqueous solution containing at least a metal compound containing nickel and a metal compound containing manganese and an ammonium ion feeder is controlled so that the pH value becomes 12.0 to 14.0 based on a liquid temperature of 25 ° C. A nucleation step in which nucleation is performed in an oxidizing atmosphere with an oxygen concentration of more than 1% by volume.
A metal compound containing at least nickel, a metal compound containing manganese, and an ammonium ion feeder are supplied to the aqueous solution for particle growth containing nuclei formed in the nucleation step, and the pH value at a liquid temperature of 25 ° C. is adjusted. A seed particle generation step in which seed particles are generated by controlling the pH value to be 10.5 to 12.0 and lower than the pH value in the nucleus generation step.
A metal compound containing at least nickel, a metal compound containing manganese, and an ammonium ion feeder are supplied to the particle growth slurry containing the seed particles formed in the seed particle generation step, and oxygen is generated from the oxidizing atmosphere. It is provided with a particle growth step of switching to a non-oxidizing atmosphere having a concentration of 1% by volume or less and growing the seed particles.
The centrifugal sedimentation density of the seed particles obtained by dividing the solid content density (g / L) of the slurry ^{by the centrifuge sedimentation volume (cm 3} / L) of the slurry is controlled to ^{0.39 g / cm 3 or less.} It is characterized by that.

In the present invention, it is important to control the centrifugal sedimentation density of the seed particles to 0.39 g / cm ^{3 or less.} The nickel-cobalt-manganese composite hydroxide particles obtained by the above production method (hereinafter, may be referred to as "composite hydroxide particles") are composed of secondary particles formed by agglomeration of primary particles, and are secondary particles. An aggregate of fine and coarse primary particles existing in the central part of the body (hereinafter, may be referred to as "central part") and an aggregate of fine primary particles surrounding the aggregate of primary particles (hereinafter, "outer shell part"). There are times when.) Is provided. In the sintering process of the positive electrode active material manufacturing process, this composite hydroxide proceeds from a lower temperature in the central portion than in the outer shell portion, and the primary particles in the central portion proceed in sintering from the center of the secondary particles. It contracts toward the slow outer shell. Further, since the central portion has a low density, the shrinkage rate is also large, the central portion becomes a space having a sufficient size, and a hollow portion is formed inside the positive electrode active material.

That is, the seed particles generated in the seed particle generation step form the central portion, and ^{by controlling the centrifugal sedimentation density of the seed particles to 0.39 g / cm 3} or less, the central portion is sufficient. The structure has a larger number of gaps in which fine primary particles are connected to each other, and a large amount of shrinkage is exhibited in the sintering step, and the obtained positive electrode active material has a hollow portion having a sufficiently large size. Further, since the number of fine primary particles increases in the central portion, the size of the primary particles in the outer shell portion also decreases, and the outer portion of the positive electrode active material becomes thin. As a result, the amount of oil absorbed by the positive electrode active material becomes large, and when used in a battery, it exhibits excellent output characteristics.

In the specification of the present invention, "oil absorption" means the amount of DBP absorbed measured in accordance with JIS K6217-4: 2008.

For the centrifugal sedimentation density, the solid content density (g / L) of the particle growth slurry containing the seed particles formed in the seed particle generation step is ^{divided by the centrifuge sedimentation volume (cm 3} / L) of the slurry. It is obtained by doing so. For the solid content density, the particle growth slurry is solid-liquid separated and the mass of the solid content is measured, or the amount of hydroxide is calculated from the total amount of metal salts supplied by the end of the seed particle generation step. It can be obtained by dividing the mass of the solid content in the slurry obtained by the above method by the volume of the slurry. Further, the centrifuge sedimentation volume can be determined by sedimenting the solid content in the slurry with a centrifuge to determine the volume of the solid content, and dividing by the volume of the slurry sedimented with the centrifuge.

When the centrifugal sedimentation density ^{exceeds 0.39 g / cm 3} , it is shown that the primary particles forming the central portion of the composite hydroxide are not sufficiently fine and the gaps are also reduced, which is sufficient for the positive electrode active material. A hollow part of a large size cannot be obtained.

The centrifugal sedimentation density can be controlled by the crystallization conditions of the nucleation step and the seed particle formation step, particularly the pH value, the ammonia concentration, and the slurry concentration. Specifically, the centrifugal sedimentation density can be controlled ^{to 0.39 g / cm 3} or less by increasing the pH value, decreasing the ammonia concentration, or decreasing the slurry concentration within the range of each step. Here, the slurry density is equivalent to the solid content density. Hereinafter, a method for producing nickel-manganese composite hydroxide particles will be described.

The method for producing composite hydroxide particles of the present invention is a method for producing nickel-manganese composite hydroxide particles by a crystallization reaction, in which a) a nucleation step for nucleation and b) seed particles are produced. It is composed of a seed particle generation step and c) a particle growth step of growing the seed particles generated in the seed particle generation step.

That is, in the conventional continuous crystallization method, the nucleation reaction and the particle growth reaction proceed simultaneously in the same tank, so that the particle size distribution of the obtained composite hydroxide particles becomes wide. On the other hand, in the method for producing composite hydroxide particles of the present invention, the time when the nucleation reaction mainly occurs (nuclear generation step) and the time when the particle growth reaction mainly occurs (particle growth step) are clearly separated. As a result, the obtained composite hydroxide particles are characterized in that they achieve a narrow particle size distribution. Further, the particle structure of the composite hydroxide particles obtained by controlling the atmosphere during the crystallization reaction is composed of a central portion composed of fine primary particles and an outer shell portion composed of primary particles larger than the central portion. It is characterized by the fact that it is made.

First, an outline of the method for producing composite hydroxide particles of the present invention will be described with reference to FIG. In FIGS. 1 and 2, (A) corresponds to the nucleation step, (B) corresponds to the seed particle forming step, and (C) corresponds to the particle growth step.

(Nucleation process)
As shown in FIG. 1, first, a plurality of metal compounds containing nickel and manganese are dissolved in water at a predetermined ratio to prepare a mixed aqueous solution. In the method for producing composite hydroxide particles of the present invention, the composition ratio of each metal in the obtained composite hydroxide particles is the same as the composition ratio of each metal in the mixed aqueous solution.

Therefore, the ratio of the metal compound to be dissolved in water is adjusted so that the composition ratio of each metal in the mixed aqueous solution is the same as the composition ratio of each metal in the composite hydroxide particles of the present invention. Make a mixed aqueous solution.

On the other hand, an alkaline aqueous solution such as an aqueous sodium hydroxide solution, an aqueous ammonia solution containing an ammonium ion feeder, and water are supplied to the reaction vessel and mixed to form an aqueous solution. The pH value of this aqueous solution (hereinafter referred to as "reaction aqueous solution") is adjusted to 12.0 to 14.0, preferably 12.3 to 13 based on a liquid temperature of 25 ° C. by adjusting the supply amount of the alkaline aqueous solution. Adjust so that it is in the range of 5.5, more preferably 12.5 to 13.0. Further, the concentration of ammonium ions in the pre-reaction aqueous solution is adjusted to 3 to 25 g / L, preferably 5 to 20 g / L by adjusting the supply amount of the aqueous ammonia solution. The temperature of the reaction aqueous solution is also adjusted to preferably 20 ° C. or higher, more preferably 20 to 60 ° C. At this time, the atmosphere in the reaction vessel is adjusted to an oxidizing atmosphere. The pH value of the aqueous solution in the reaction vessel and the concentration of ammonium ions can be measured with a general pH meter and ion meter, respectively.

When the temperature and pH of the reaction aqueous solution are adjusted in the reaction vessel, the mixed aqueous solution is supplied into the reaction vessel while stirring the reaction aqueous solution. As a result, a reaction aqueous solution mixed with the mixed aqueous solution, that is, a nucleation aqueous solution which is a reaction aqueous solution in the nucleation step is formed in the reaction vessel, and fine nuclei of the composite hydroxide are formed in the nucleation aqueous solution. Will be generated. At this time, since the pH value of the nucleation aqueous solution is in the above range, the nucleated nuclei hardly grow, and the nucleation occurs preferentially.

Since the pH value and the concentration of ammonium ions of the nucleation aqueous solution change with the nucleation caused by the supply of the mixed aqueous solution, an alkaline aqueous solution and an ammonia aqueous solution are supplied to the nucleating aqueous solution together with the mixed aqueous solution. The pH value of the aqueous solution for nucleation is controlled to be maintained in the range of 12.0 to 14.0 based on the liquid temperature of 25 ° C., and the concentration of ammonium ions is controlled to be maintained in the range of 3 to 25 g / L.

By supplying the mixed aqueous solution, the alkaline aqueous solution and the ammonia aqueous solution to the nucleation aqueous solution, the generation of new nuclei is continuously continued in the nucleation aqueous solution. Then, when a predetermined amount of nuclei are generated in the nucleation aqueous solution, the nucleation step is completed. Whether or not a predetermined amount of nuclei have been generated is determined by the amount of metal salt added to the nucleation aqueous solution.

(Seed particle generation process)
After the completion of the nucleation step, the pH value of the aqueous solution for nucleation is adjusted to 10.5 to 12.0, preferably 11.0 to 12.0 based on a liquid temperature of 25 ° C. while maintaining an oxidizing atmosphere. To obtain an aqueous solution for particle growth, which is a reaction aqueous solution in the particle growth step. Specifically, the pH at the time of this adjustment is controlled by adjusting the supply amount of the alkaline aqueous solution.

By setting the pH value of the aqueous particle growth solution in the above range, the nuclear growth reaction takes precedence over the nuclear formation reaction. Therefore, in the seed particle generation step, a new nucleus is added to the particle growth aqueous solution. Nuclei grow and seed particles are formed with little formation.

Similarly, since the pH value of the aqueous solution for particle growth and the concentration of ammonium ions change with the formation of seed particles by supplying the mixed aqueous solution, the aqueous solution for particle growth is also supplied with the alkaline aqueous solution and the ammonia aqueous solution together with the mixed aqueous solution. Then, the pH value of the aqueous solution for particle growth is controlled to be maintained in the range of 10.5 to 12.0 and the concentration of ammonium ions is maintained in the range of 3 to 25 g / L based on the liquid temperature of 25 ° C. Then, when the seed particles have grown to a predetermined particle size, the seed particle generation step is terminated.

(Particle growth process)
After the completion of the seed particle generation step, the reaction is carried out while maintaining the pH value of the aqueous solution for particle growth at 10.5 to 12.0, preferably 11.0 to 12.0 based on the liquid temperature of 25 ° C. The atmosphere in the tank is switched from the oxidizing atmosphere to the atmosphere in the range of weakly oxidizing to non-oxidizing. By switching the atmosphere, the above-mentioned particle structure having a seed particle, that is, an outer shell portion composed of plate-shaped primary particles larger than the fine primary particles, is formed outside the central portion of the composite hydroxide particles formed by the fine primary particles. Can be formed.

Even in the particle growth step, seed particles grow (particle growth) in the particle growth aqueous solution with almost no new nuclei, and composite hydroxide particles having a predetermined particle size are formed. Similarly, the pH value of the aqueous solution for particle growth and the concentration of ammonium ions change with the growth of particles by supplying the mixed aqueous solution. Therefore, the aqueous solution for particle growth is also supplied with an alkaline aqueous solution and an aqueous ammonia solution together with the mixed aqueous solution. Therefore, the pH value of the aqueous solution for particle growth is controlled to be maintained in the range of 10.5 to 12.0 and the concentration of ammonium ions is maintained in the range of 3 to 25 g / L based on the liquid temperature of 25 ° C.

Then, when the composite hydroxide particles have grown to a predetermined particle size, the particle growth step is terminated. For the particle size of the composite hydroxide particles, the relationship between the amount of metal salt added to each reaction aqueous solution and the obtained particles in each step of the nucleation formation step, the seed particle formation step, and the particle growth step was determined by a preliminary test. If it is set, it can be easily judged from the amount of metal salt added in each process.

As described above, in the case of the above-mentioned method for producing composite hydroxide particles, nucleation occurs preferentially in the nucleation step, and nuclei growth hardly occurs. On the contrary, particles in the seed particle formation step and the particle growth step. Only growth occurs and few new nuclei are produced. Therefore, in the nucleation step, the range of particle size distribution is narrow and a homogeneous nucleus can be formed, and in the particle growth step, the nucleus can be grown homogeneously. Therefore, in the above method for producing composite hydroxide particles, nickel-manganese composite hydroxide particles having a narrow particle size distribution range and being homogeneous can be obtained. Further, by switching the atmosphere as described above, it is possible to obtain a particle structure including a central portion formed of fine primary particles and an outer shell portion formed of primary particles larger than the fine primary particles.

In the case of the above production method, since the metal ions crystallize as a composite hydroxide in both steps, the ratio of the liquid component to the metal component in each reaction aqueous solution increases. In this case, the concentration of the supplied mixed aqueous solution apparently decreases, and there is a possibility that the composite hydroxide particles do not grow sufficiently, especially in the particle growth step.

Therefore, in order to suppress the increase of the liquid component, it is preferable to discharge a part of the liquid component in the aqueous solution for particle growth to the outside of the reaction vessel from the end of the nucleation step to the middle of the particle growth step. Specifically, the supply and stirring of the mixed aqueous solution, the alkaline aqueous solution and the ammonia aqueous solution with respect to the aqueous solution for particle growth are stopped, the nuclei and the composite hydroxide particles are precipitated, and the supernatant of the aqueous solution for particle growth is discharged. Thereby, the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth can be increased. Then, since the composite hydroxide particles can be grown in a state where the relative concentration of the mixed aqueous solution is high, the particle size distribution of the composite hydroxide particles can be narrowed, and the secondary of the composite hydroxide particles can be narrowed. The density of the particles as a whole can also be increased.

Further, in the embodiment shown in FIG. 1, the pH of the nucleation aqueous solution for which the nucleation step has been completed is adjusted to form a particle growth aqueous solution, and the nucleation step is followed by the particle growth step. There is an advantage that the transition to the particle growth process can be performed quickly. Further, the transition from the nucleation step to the particle growth step can be performed only by adjusting the pH of the reaction aqueous solution, and the pH can be easily adjusted by temporarily stopping the supply of the alkaline aqueous solution. There is. The pH of the reaction aqueous solution can also be adjusted by adding sulfuric acid to the reaction aqueous solution in the case of an inorganic acid of the same type as the acid constituting the metal compound, for example, sulfate.

However, separately from the aqueous solution for nucleation, a component-adjusted aqueous solution adjusted to a pH and ammonium ion concentration suitable for the particle growth step is formed, and the component-adjusted aqueous solution is subjected to a nucleation step in another reaction vessel. An aqueous solution containing nuclei (an aqueous solution for nucleation, preferably an aqueous solution for nucleation from which a part of a liquid component is removed) is added to obtain a reaction aqueous solution, and this reaction aqueous solution is used as an aqueous solution for particle growth for particle growth. The process may be performed. It is also possible to carry out the seed particle generation step in another reaction tank.

When the particle growth step is carried out in another reaction tank, the nucleation step and the particle growth step can be separated more reliably, so that the state of the reaction aqueous solution in each step is the optimum condition for each step. be able to. In particular, the pH of the aqueous particle growth solution can be set as the optimum condition from the start of the particle growth step. The nickel-manganese composite hydroxide particles formed in the particle growth step can have a narrower particle size distribution range and be homogeneous. Next, the control of the reaction atmosphere in each step, the substances and solutions used in each step, and the reaction conditions will be described in detail.

(Reaction atmosphere)
The particle structure of the nickel-manganese composite hydroxide particles of the present invention is formed by controlling the atmosphere in the reaction vessel in the nucleation generation step, the seed particle formation step, and the particle growth step. Therefore, the atmosphere control in each step of the manufacturing method has an important meaning. When the inside of the reaction vessel during the crystallization reaction is in an oxidizing atmosphere, the growth of the primary particles forming the nickel-manganese composite hydroxide particles is controlled, and low-density particles formed by fine primary particles and having many voids are formed. In a weakly oxidizing atmosphere to a non-oxidizing atmosphere, the primary particles are large, and dense and dense particles are formed.

That is, by setting the nucleation step and the seed particle formation step to an oxidizing atmosphere, a central portion composed of fine primary particles is formed, and in the subsequent particle growth step, the atmosphere is switched from the oxidizing atmosphere to weakly oxidizing to non-oxidizing. By setting the atmosphere in the range, it is possible to form the above-mentioned particle structure having an outer shell portion composed of plate-shaped primary particles larger than the fine primary particles on the outside of the central portion.

In the atmosphere-controlled crystallization reaction, the primary particles in the central portion usually have a fine plate-like shape and / or needle-like shape, and the primary particles in the outer shell portion have a plate-like shape. However, the primary particles of the nickel-manganese composite hydroxide may have shapes such as a rectangular parallelepiped, an ellipse, and a ridge surface depending on the composition.

The oxidizing atmosphere for forming the central portion in the present invention is defined as an atmosphere in which the oxygen concentration in the reaction vessel space exceeds 1% by volume. An oxidizing atmosphere having an oxygen concentration of more than 2% by volume is preferable, an oxidizing atmosphere having an oxygen concentration of more than 10% by volume is more preferable, and an air atmosphere (oxygen concentration: 21% by volume) that is easy to control is particularly preferable. By creating an atmosphere in which the oxygen concentration exceeds 1% by volume, the average particle size of the primary particles can be set to 0.01 to 0.3 μm. When the oxygen concentration is 1% by volume or less, the average particle size of the primary particles in the central portion may exceed 0.3 μm. The upper limit of the oxygen concentration is not particularly limited, but if it exceeds 30% by volume, the average particle size of the primary particles may be less than 0.01 μm, which is not preferable.

On the other hand, the atmosphere in the range of weakly oxidizing to non-oxidizing for forming the outer shell portion in the present invention is defined as an atmosphere in which the oxygen concentration in the space inside the reaction vessel is 1% by volume or less. The mixed atmosphere of oxygen and an inert gas is controlled so that the oxygen concentration is preferably 0.5% by volume or less, more preferably 0.2% by volume or less. By growing the particles with the oxygen concentration in the reaction tank space set to 1% by volume or less, unnecessary oxidation of the particles is suppressed, the growth of the primary particles is promoted, and the average particle size is larger than the central portion of 0.3 to 3 μm. It is possible to obtain secondary particles having a dense and high-density outer shell portion having a uniform particle size with a primary particle size. As a means for maintaining the space inside the reaction tank in such an atmosphere, it is possible to distribute an inert gas such as nitrogen to the space inside the reaction tank, and to bubbling the inert gas in the reaction solution. ..

The atmosphere is switched in the particle growth step at the center of the nickel-manganese composite hydroxide particles so that a hollow portion is obtained in the finally obtained positive electrode active material to the extent that fine particles are not generated and the cycle characteristics are not deteriorated. The timing is determined in consideration of the size of. For example, the total particle growth step time is in the range of 0 to 40%, preferably 0 to 30%, and more preferably 0 to 25% from the start of the particle growth step. If the above switching is performed when the total particle growth process time exceeds 30%, the formed central portion becomes large, and the thickness of the outer shell portion relative to the particle size of the secondary particles may become too thin. is there. On the other hand, if the above switching is performed before the start of the particle growth step, that is, during the nucleation step, the central portion becomes too small or secondary particles having the above structure are not formed.

(PH control)
As described above, in the nucleation step, it is necessary to control the pH value of the reaction aqueous solution to be in the range of 12.0 to 14.0, preferably 12.3 to 13.5 based on the liquid temperature of 25 ° C. There is. When the pH value exceeds 14.0, there is a problem that the generated nuclei become too fine and the reaction aqueous solution gels. On the other hand, if the pH value is less than 12.0, the growth reaction of the nucleus occurs along with the nucleation, so that the range of the particle size distribution of the formed nucleus becomes wide and becomes inhomogeneous. That is, in the nucleation step, by controlling the pH value of the reaction aqueous solution within the above range, the growth of nuclei can be suppressed and almost only nucleation can occur, and the nuclei formed are also in the range of homogeneous and particle size distribution. Can be narrow.

On the other hand, in the seed particle generation step and the particle growth step, the pH value of the reaction aqueous solution is controlled to be in the range of 10.5 to 12.0, preferably 11.0 to 12.0 based on the liquid temperature of 25 ° C. There is a need to. When the pH value exceeds 12.0, the number of newly generated nuclei increases and fine secondary particles are generated, so that hydroxide particles having a good particle size distribution cannot be obtained. Further, when the pH value is less than 10.5, the solubility of ammonia ions is high, and the amount of metal ions remaining in the liquid without precipitation increases, so that the production efficiency deteriorates. That is, in the particle growth step, by controlling the pH of the reaction aqueous solution within the above range, only the growth of the nuclei generated in the nucleation step can be preferentially caused, and new nucleation can be suppressed. The nickel-manganese composite hydroxide particles to be obtained can be made homogeneous and have a narrow range of particle size distribution.

In any of the nucleation step, the seed particle forming step, and the particle growing step, the fluctuation range of pH is preferably within 0.2 above and below the set value. When the pH fluctuation range is large, nucleation and particle growth may not be constant, and uniform manganese composite hydroxide particles having a narrow particle size distribution range may not be obtained.

When the pH value is 12, it is a boundary condition between nucleation and nucleation. Therefore, depending on the presence or absence of nuclei present in the reaction aqueous solution, either the nucleation step or the seed particle formation step can be used. it can.

That is, if the pH value in the nucleation step is set to higher than 12 to generate a large amount of nuclei and then the pH value is set to 12 in the seed particle generation step, a large amount of nuclei are present in the reaction aqueous solution, so that nucleation grows. It occurs preferentially, and the hydroxide particles having a narrow particle size distribution and a relatively large particle size can be obtained.

On the other hand, when there are no nuclei in the reaction aqueous solution, that is, when the pH value is set to 12 in the nucleation step, nucleation occurs preferentially because there are no nuclei to grow, and the pH value in the particle growth step is set to 12. By making the size smaller, the generated nuclei grow and good hydroxide particles are obtained.

In either case, the pH values of the seed particle generation step and the particle growth step may be controlled to be lower than the pH value of the nucleation step, and in order to clearly separate the nucleation and the particle growth, the seed particle generation The pH value of the step and the particle growth step is preferably 0.5 or more lower than the pH value of the nucleation step, and more preferably 1.0 or more.

(Nucleation amount)
The amount of nuclei produced in the nucleation step is not particularly limited, but in order to obtain composite hydroxide particles having a good particle size distribution, the total amount, that is, to obtain composite hydroxide particles It is preferably 0.1% to 2%, more preferably 1.5% or less of the total metal salt to be supplied.

(Control of particle size of composite hydroxide particles)
Since the particle size of the composite hydroxide particles can be controlled by the total time of the seed particle generation step and the particle growth step, if the particle growth step is continued until the particles grow to the desired particle size, the desired particle size can be obtained. Composite hydroxide particles can be obtained.

Further, the particle size of the composite hydroxide particles can be controlled not only by the seed particle generation step and the particle growth step, but also by the pH value of the nucleation step and the amount of raw material input for nucleation.

That is, by setting the pH at the time of nucleation to the high pH value side or by lengthening the nucleation time, the amount of raw material to be input is increased and the number of nuclei to be produced is increased. As a result, the particle size of the composite hydroxide particles can be reduced even when the particle growth step is the same condition.

On the other hand, if the number of nucleated particles is controlled to be small, the particle size of the obtained composite hydroxide particles can be increased.

Conditions such as the metal compound, the concentration of ammonia in the reaction aqueous solution, and the reaction temperature will be described below, but the difference between the nucleation step and the particle growth step is only in the range of controlling the pH of the reaction aqueous solution and the atmosphere in the reaction vessel. Yes, the conditions such as the metal compound, the concentration of ammonia in the reaction solution, and the reaction temperature are substantially the same in both steps.

(Metal compound)
As the metal compound, a compound containing the target metal is used. The compound to be used is preferably a water-soluble compound, and examples thereof include nitrates, sulfates, and hydrochlorides. For example, nickel sulfate, manganese sulfate, and cobalt sulfate are preferably used.

(Additional element)
As the additive element (one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W), it is preferable to use a water-soluble compound, for example, titanium sulfate, peroxo. Ammonium titanate, potassium titanium oxalate, 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. ..

When such an additive element is uniformly dispersed inside the composite hydroxide particles, an additive containing the additive element may be added to the mixed aqueous solution, and the additive element may be uniformly dispersed inside the composite hydroxide particles. It can be co-sunk in a dispersed state.

When the surface of the composite hydroxide particles is coated with an additive element, for example, the composite hydroxide particles are slurried with an aqueous solution containing the additive element, and the pH is controlled to a predetermined pH. If an aqueous solution containing one or more of the additive elements is added and the additive elements are precipitated on the surface of the composite hydroxide particles by a crystallization reaction, the surface can be uniformly coated with the additive elements. In this case, an alkoxide solution of the additive element may be used instead of the aqueous solution containing the additive element. Further, the surface of the composite hydroxide particles can be coated with the additive element by spraying an aqueous solution or a slurry containing the additive element on the composite hydroxide particles to dry the composite hydroxide particles. Further, the slurry in which the composite hydroxide particles and the salt containing the one or more additive elements are suspended is spray-dried, or the composite hydroxide and the salt containing the one or more additive elements are mixed by the solid phase method. It can be coated by a method such as

When the surface is coated with an additive element, the atomic number ratio of the metal ions of the composite hydroxide particles obtained by reducing the atomic number ratio of the additive element ions present in the mixed aqueous solution by the amount to be coated is reduced. Can be matched with. Further, the step of coating the surface of the particles with the additive element may be performed on the particles after heating the composite hydroxide particles.

(Concentration of mixed aqueous solution)
The total concentration of the mixed aqueous solution of the metal compounds is preferably 1 to 2.6 mol / L, preferably 1.5 to 2.2 mol / L. If the concentration of the mixed aqueous solution is less than 1 mol / L, the amount of crystallized substances per reaction vessel is small, so that the productivity is lowered, which is not preferable.

On the other hand, if the salt concentration of the mixed aqueous solution exceeds 2.6 mol / L, the saturation concentration at room temperature is exceeded, and there is a risk that crystals will reprecipitate and clog the equipment piping.

Further, the metal compound does not necessarily have to be supplied to the reaction tank as a mixed aqueous solution. For example, when a metal compound that reacts to form a compound when mixed is used, the total concentration of the total metal compound aqueous solution is within the above range. As such, an aqueous solution of a metal compound may be individually prepared and supplied into the reaction vessel at a predetermined ratio as an aqueous solution of the individual metal compounds at the same time.

Further, the amount of the mixed aqueous solution or the like or the aqueous solution of each metal compound supplied to the reaction vessel is such that the concentration of the crystallized product at the time when the crystallization reaction is completed is approximately 30 to 200 g / L, preferably 80 to 150 g / L. It is desirable to be. 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 200 g / L, the mixed aqueous solution to be added is sufficiently diffused in the reaction vessel. This is because the particle growth may be biased.

(Ammonia concentration)
The ammonia concentration in the reaction aqueous solution is preferably maintained at a constant value within the range of 3 to 25 g / L, preferably 5 to 20 g / L so as not to cause the following problems.

Since ammonia acts as a complexing agent, if the ammonia concentration is less than 3 g / L, the solubility of metal ions cannot be kept constant, and plate-shaped hydroxide primary particles with a uniform shape and particle size. Is not formed and gel-like nuclei are likely to be formed, so that the particle size distribution is likely to spread.

On the other hand, when the ammonia concentration exceeds 25 g / L, the solubility of the metal ions becomes too large, the amount of the metal ions remaining in the reaction aqueous solution increases, and the composition shifts.

Further, when the ammonia concentration fluctuates, the solubility of metal ions fluctuates and uniform hydroxide particles are not formed. Therefore, it is preferable to keep the value constant. For example, the ammonia concentration is preferably maintained at a desired concentration with the upper and lower limits set to about 5 g / L.

The ammonium ion feeder is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used.

(Reaction solution temperature)
In the reaction vessel, the temperature of the reaction solution is preferably set to 20 ° C. or higher, particularly preferably 20 to 60 ° C. When the temperature of the reaction solution is less than 20 ° C., the solubility is low, so that nucleation is likely to occur and control becomes difficult. On the other hand, if the temperature exceeds 60 ° 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.

(Alkaline aqueous solution)
The alkaline aqueous solution for adjusting the pH in the reaction aqueous solution is not particularly limited, and for example, an alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. In the case of such an alkali metal hydroxide, it may be directly supplied into the reaction aqueous solution, but it is preferable to add it as an aqueous solution to the reaction aqueous solution in the reaction tank because of the ease of pH control of the reaction aqueous solution in the reaction tank. ..

The method of adding the alkaline aqueous solution to the reaction vessel is not particularly limited, and the pH value of the reaction aqueous solution is predetermined by a pump such as a metering pump that can control the flow rate while sufficiently stirring the reaction aqueous solution. It may be added so as to be maintained in the range of.

(production equipment)
In the method for producing composite hydroxide particles of the present invention, an apparatus of a method in which the product is not recovered until the reaction is completed is used. For example, a commonly used batch reaction vessel equipped with a stirrer. When such a device is adopted, unlike a continuous crystallizer that recovers products by overflow, there is no problem that growing particles are recovered at the same time as the overflow liquid, so that the particle size distribution is narrow and the particle size is small. Aligned particles can be obtained.

Further, since it is necessary to control the reaction atmosphere, an atmosphere controllable device such as a closed type device is used. By using such an apparatus, the obtained composite hydroxide particles can have the above-mentioned structure, and the nucleation reaction and the particle growth reaction can proceed almost uniformly, so that the particle size distribution is excellent. It is possible to obtain fine particles, that is, particles having a narrow particle size distribution range.

The composition of the nickel-manganese composite hydroxide particles obtained by the above production method is adjusted so as to be represented by the following general formula. If a lithium nickel-manganese composite oxide is produced using nickel-manganese composite hydroxide particles having such a composition as a precursor, when an electrode using this lithium nickel-manganese composite oxide as a positive electrode active material is used in a battery. , The value of the measured positive electrode resistance can be lowered, excellent output characteristics can be exhibited, and the battery performance can be improved.

General formula: Ni _x Mn _y Co _z M _t (OH) _{2 + α}
(X + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ α ≦ 0.5, M Is an additive element, and is one or more additive elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W).
In the present invention, when a positive electrode active material having a hollow structure is to be obtained, the nickel content and the manganese content of the nickel-manganese composite hydroxide particles, which are precursors thereof, are determined by the above general formulas, respectively. By adjusting so that 0.3 ≦ x ≦ 0.7 and 0.1 ≦ y ≦ 0.55 and setting the manganese content higher, the secondary particles from which the hollow structure can be easily obtained can be obtained. Can be a nickel composite hydroxide.

When a positive electrode active material is obtained from the composite hydroxide particles as a raw material, the composition ratio (Ni: Mn: Co: M) of the composite hydroxide particles is maintained even in the obtained positive electrode active material. Therefore, the composition ratio of the composite hydroxide of the present invention is adjusted to be similar to the composition ratio required for the positive electrode active material to be obtained.

(Average particle size)
The average particle size of the nickel-manganese composite hydroxide particles of the present invention is adjusted to a range of more than 1 μm and 15 μm or less, preferably an average particle size of more than 3 μm and 10 μm or less. By controlling the average particle size of the nickel composite hydroxide within such a range, the positive electrode active material obtained from the composite hydroxide particles as a raw material is adjusted to a predetermined average particle size (more than 1 μm and 15 μm or less). can do. As described above, since the particle size of the composite hydroxide particles correlates with the particle size of the obtained positive electrode active material, it affects the characteristics of the battery using this positive electrode active material as the positive electrode material.

When the average particle size of this composite hydroxide is 1 μm or less, the average particle size of the obtained positive electrode active material is also small, and a high output can be obtained by increasing the surface area, but the packing density of the positive electrode is lowered. The battery capacity per volume decreases, the dispersibility with the conductive auxiliary agent deteriorates when the electrode paste is confused, and the voltage applied to the particles in the electrode becomes non-uniform, which deteriorates when charging and discharging are repeated. , Capacity drops. On the contrary, when the average particle size of the composite hydroxide exceeds 15 μm, the specific surface area of the obtained positive electrode active material decreases and the interface with the electrolytic solution decreases, so that the resistance of the positive electrode increases and the battery The output characteristics of

(Particle size distribution)
The composite hydroxide particles of the present invention are adjusted so that [(d90-d10) / average particle size], which is an index showing the spread of the particle size distribution, is 1.0 or less, preferably 0.70 or less. ing. The particle size distribution of the positive electrode active material is strongly influenced by the composite hydroxide as a raw material. For example, when fine particles or coarse particles are mixed in the composite hydroxide particles, the positive electrode active material also has fine particles. Alternatively, coarse particles will be present. That is, when [(d90-d10) / average particle size] exceeds 1.0 and the particle size distribution is wide, fine particles or coarse particles are also present in the positive electrode active material.

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 lowers the safety of the battery and selectively deteriorates the fine particles. Therefore, the cycle characteristics of the battery deteriorate. 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.

The average particle size and d90 and d10 can be obtained from the volume integrated values measured by the laser light diffraction scattering type particle size analyzer. In the index [(d90-d10) / average particle size] indicating the spread of the particle size distribution, d10 accumulates the number of particles at each particle size from the smaller particle size side, and the cumulative volume is 10 of the total volume of all particles. It means the particle size to be%. Further, d90 means a particle size in which the number of particles is similarly accumulated and the accumulated volume is 90% of the total volume of all particles. As the average particle size, the volume average particle size MV may be used, and may be used.

(Particle structure)
The transition metal composite hydroxide particles of the present invention are composed of secondary particles formed by aggregating a plurality of primary particles. As the shape of the primary particles constituting the secondary particles, various forms such as a plate shape, a needle shape, a rectangular parallelepiped shape, an elliptical shape, and a ridge face shape can be adopted. Further, the agglutination state can be applied to the present invention not only in the case of agglutination in a random direction but also in the case of agglomeration of particles in the major axis direction radially from the center.

However, in the present invention, it is preferable that the plate-shaped and / or needle-shaped primary particles are aggregated in random directions to form secondary particles. In the case of such a structure, voids are formed almost uniformly between the primary particles, and when the lithium compound is mixed and fired, the molten lithium compound spreads into the secondary particles and the lithium is sufficiently diffused. Because it is done.

In the present invention, the average particle size of the primary particles constituting the secondary particles is preferably adjusted to the range of 0.3 to 3.0 μm. By adjusting the size of the primary particles in this way, appropriate voids are obtained between the primary particles, and sufficient diffusion of lithium into the secondary particles during firing is easily performed. The average particle size of the primary particles is more preferably 0.4 to 1.5 μm.

When the average particle size of the primary particles is less than 0.3 μm, the sintering temperature at the time of firing is lowered, the sintering between the secondary particles is increased, and the obtained positive electrode active material contains coarse particles. Become. On the other hand, if it exceeds 3 μm, it becomes necessary to raise the firing temperature in order to make the obtained positive electrode active material sufficiently crystalline, and firing at such a high temperature results in firing between secondary particles. Sintering will occur and the positive electrode active material will deviate from the appropriate particle size distribution.

In the present invention, as the structure of the secondary particles of the positive electrode active material, a hollow structure having a dense and thin outer shell and a hollow inside is adopted. On the other hand, as a precursor of the positive electrode active material having a hollow structure, a central portion, which is an aggregate of fine and coarse primary particles forming a hollow, and an outer shell portion, which is an aggregate of dense primary particles on the outer periphery surrounding the central portion, are used. Be prepared.

In such a particle structure, the properties of the primary particles have an effect. That is, it is preferable that fine primary particles are agglomerated in a random direction in the central portion, and larger primary particles are agglomerated in a random direction in the outer shell portion. Due to the aggregation in such random directions, the contraction of the central portion is uniformly generated, and a space having a sufficient size can be formed in the positive electrode active material.

In this case, the average particle size of the fine primary particles is preferably 0.01 to 0.3 μm, more preferably 0.1 to 0.3 μm. If the average particle size of the fine primary particles is less than 0.01 μm, a central portion of sufficient size may not be formed in the composite hydroxide particles, and if it exceeds 0.3 μm, the temperature at the start of sintering is lowered and shrinkage occurs. Is not enough, and a space of sufficient size may not be obtained after firing. The properties of the primary particles in the outer shell may be the same as described above.

The secondary particles constituting the positive electrode active material obtained from such composite hydroxide particles as a raw material have a hollow structure, and the ratio of the thickness of the outer shell portion to the particle diameter is the above-mentioned composite hydroxide secondary. The ratio of subatomic particles is generally maintained. Therefore, by setting the ratio of the thickness of the outer shell portion to the secondary particle size in the above range, a sufficient hollow portion can be formed in the lithium transition metal composite oxide.

The particle size of the fine primary particles in the center and the larger primary particles in the outer shell, and the thickness of the outer shell are observed by observing the cross section of the transition metal composite hydroxide using a scanning electron microscope. It can be measured by. For example, a plurality of transition metal composite hydroxides (secondary particles) are embedded in a resin or the like, and the cross-section of the particles can be observed by cross-section polisher processing or the like. For the particle size of the fine primary particles in the central portion and the primary particles in the outer shell portion, the maximum diameter of preferably 10 or more primary particle cross sections in the secondary particles is measured as the particle size, and the average value is calculated. Can be found at.

The ratio of the thickness of the outer shell to the secondary particle size can be obtained as follows. From the secondary particles in the resin, particles whose cross section can be observed at the center of the particles are selected, and the distance between the outer circumference of the outer shell and the inner circumference on the center side is set at three or more arbitrary points. The shortest distance between two points is measured to obtain the average thickness of the outer shell for each particle. The above ratio of the thickness of the outer shell portion for each particle is obtained by dividing the average thickness by using the distance between any two points having the maximum distance on the outer circumference of the secondary particle as the secondary particle diameter. Further, by averaging the ratio of each particle obtained for 10 or more particles, the ratio of the thickness of the outer shell portion to the secondary particle size in the nickel composite hydroxide can be obtained.

(2) Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery The method for producing the positive electrode active material of the present invention is a lithium mixture obtained by mixing nickel cobalt manganese composite hydroxide particles obtained by the above production method and a lithium compound. A mixing step of forming the above and a firing step of firing the mixture formed in the mixing step are included, but a heat treatment step of heat-treating the transition metal composite hydroxide may be added before the mixing step. That is, as shown in FIG. 2, a) a heat treatment step of heat-treating nickel-cobalt-manganese composite hydroxide particles which are precursors of a positive electrode active material, and b) a lithium compound is mixed with the heat-treated particles to form lithium. It may include a mixing step of forming a mixture, and c) a firing step of firing the mixture formed in the mixing step. Hereinafter, each step will be described.

a) Heat treatment step The heat treatment step is a step of heating the composite hydroxide particles obtained by the above method for producing nickel-cobalt-manganese composite hydroxide particles to a temperature of 105 to 750 ° C., preferably 105 to 400 ° C. for heat treatment. is there. By performing this heat treatment step, the water contained in the composite hydroxide particles is removed. By performing this heat treatment step, the amount of water remaining in the particles until the firing step can be reduced to a certain amount. Therefore, it is possible to prevent variations in the number of metal atoms and the ratio of lithium atoms in the obtained positive electrode active material.

It is only necessary to remove water to the extent that the number of metal atoms and the ratio of lithium atoms in the positive electrode active material do not vary, so it is not always necessary to convert all composite hydroxides to transition metal composite oxides. However, heat treatment at a temperature of 400 ° C. or lower is sufficient, but in order to further reduce the variation, all the composite hydroxides may be converted into composite oxides at a heating temperature of 400 ° C. or higher. In the firing step, which is a subsequent step, the oxide is converted to a composite oxide during heating, but the above variation can be suppressed by heat treatment.

In the heat treatment step, when the heating temperature is less than 105 ° C., excess water in the composite hydroxide cannot be removed, and the above variation may not be suppressed. On the other hand, when the heating temperature exceeds 750 ° C., the particles are sintered by the heat treatment and a composite oxide having a uniform particle size cannot be obtained. The above variation can be suppressed by determining the metal component contained in the composite hydroxide under the heat treatment conditions in advance by analysis and determining the ratio with the lithium compound.

The atmosphere in which the heat treatment is performed is not particularly limited and may be a non-reducing atmosphere, but it is preferably performed in an air stream that can be easily performed.

The heat treatment time is not particularly limited, but if it is less than 1 hour, the excess water of the composite hydroxide may not be sufficiently removed. Therefore, at least 1 hour or more is preferable, and 5 to 15 hours is more preferable.

The equipment used for the heat treatment is not particularly limited, as long as the composite hydroxide can be heated in a non-reducing atmosphere, preferably in an air stream, such as an electric furnace that does not generate gas. Is preferably used.

b) Mixing step The mixing step includes transition metal composite hydroxide particles, composite hydroxide particles heat-treated in the heat treatment step (hereinafter, may be referred to as “heat-treated particles”), and a substance containing lithium. For example, it is a step of mixing with a lithium compound to obtain a lithium mixture.

Here, the heat-treated particles include not only composite hydroxides from which residual water has been removed in the heat treatment step, but also composite oxides converted into oxides in the heat treatment step, or mixed particles thereof.

The transition metal composite hydroxide or heat-treated particles and the lithium compound are the sum of the number of atoms of a metal other than lithium in the lithium mixture, that is, the sum of the number of atoms of nickel, manganese, cobalt and additive elements (Me), and lithium. The mixture is mixed so that the ratio (Li / Me) to the number of atoms (Li) is 0.95 to 1.5, preferably 1-1.35, and more preferably 1-1.20. That is, since Li / Me usually does not change before and after the firing step, the Li / Me mixed in this mixing step becomes Li / Me in the positive electrode active material, so that the Li / Me in the lithium mixture is the positive electrode to be obtained. It is mixed so as to be the same as Li / Me in the active material.

The lithium compound used to form the lithium mixture is not particularly limited, but for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferable in that it is easily available. .. In particular, considering ease of handling and stability of quality, it is more preferable to use lithium hydroxide, lithium carbonate, or a mixture thereof.

The lithium mixture is preferably sufficiently mixed before firing. If the mixing is not sufficient, problems such as variations in Li / Me among the individual particles and insufficient battery characteristics may occur.

In addition, a general mixer can be used for mixing, for example, a shaker mixer, a ladyge mixer, a julia mixer, a V blender, or the like can be used, to the extent that the skeleton such as the transition metal composite hydroxide is not destroyed. Then, it is sufficient that the composite oxide or the heat-treated particles and the substance containing lithium are sufficiently mixed.

c) Firing step The firing step is a step of calcining the lithium mixture obtained in the above mixing step to form a lithium transition metal composite oxide. When the lithium mixture is fired in the firing step, the lithium in the lithium-containing substance diffuses into the transition metal composite hydroxide or the heat-treated particles, so that the lithium transition metal composite oxide is formed.

(Baking temperature)
Firing of the lithium mixture is carried out at 650-1000 ° C. If the calcination temperature is less than 650 ° C., the diffusion of lithium into the transition metal composite oxide is not sufficient, and excess lithium and unreacted transition metal composite oxide remain, or the crystal structure is not sufficiently arranged. Therefore, sufficient battery characteristics cannot be obtained when used in a battery. Further, if the temperature exceeds 1000 ° C., the lithium transition metal composite oxides are violently sintered, and abnormal grain growth occurs, so that the particles become coarse and the morphology of the spherical secondary particles cannot be maintained. In either case, not only the battery capacity is reduced, but also the value of the positive electrode resistance is increased.

The firing temperature is preferably 800 to 980 ° C, more preferably 850 to 950 ° C.

(Baking time)
Of the firing times, the holding time at a predetermined temperature is preferably at least 1 hour or more, and more preferably 2 to 10 hours. In less than one hour, the formation of the lithium transition metal composite oxide may not be sufficient.

(Temporary firing)
In particular, when lithium hydroxide or lithium carbonate is used as the lithium compound, the temperature is lower than the firing temperature and is 350 to 800 ° C., preferably 450 to 780 ° C. for 1 to 10 hours before the firing step. It is preferable to hold the mixture for about 3 to 6 hours for calcining. Alternatively, by slowing the rate of temperature rise until the firing temperature is reached, it is possible to obtain substantially the same effect as in the case of calcining. That is, it is preferable to perform calcining at the reaction temperature of lithium hydroxide or lithium carbonate and the transition metal composite oxide. In this case, if lithium hydroxide or lithium carbonate is kept near the above reaction temperature, lithium is sufficiently diffused into the heat-treated particles, and a uniform lithium transition metal composite oxide can be obtained.

(Baking atmosphere)
The atmosphere at the time of firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 10 to 100% by volume, and particularly preferably a mixed atmosphere of oxygen having an oxygen concentration and an inert gas. That is, it is preferable to carry out in the atmosphere or an oxygen stream. If the oxygen concentration is less than 10% by volume, oxidation may not be sufficient and the crystallinity of the lithium transition metal composite oxide may not be sufficient.

The furnace used for firing is not particularly limited as long as it can be heated in an air to oxygen stream, but from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas is used. Preferably, a batch or continuous furnace is used.

(Crushing)
The lithium transition metal composite oxide obtained by firing may be aggregated or slightly sintered. In this case, it may be crushed, whereby a lithium transition metal composite oxide, that is, the positive electrode active material of the present invention can be obtained. In addition, crushing means that mechanical energy is applied to an agglomerate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and the secondary particles themselves are hardly destroyed. It is an operation to separate secondary particles and loosen agglomerates.

The positive electrode active material obtained by the above production method has a general formula: Li _{1 + u} Ni _x Mn _y Co _z M _t O _{2 + α} (−0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0. 7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is an additive element, and Al, Ti, V, Cr, Zr, Nb, Mo, W It is represented by one or more elements selected from), and is composed of a lithium nickel-manganese composite oxide having a hexagonal crystal structure having a layered structure.

The value of s, which indicates an excess amount of lithium in the positive electrode active material, is in the range of −0.05 to 0.50. When the excess amount s of lithium is less than −0.05, the reaction resistance of the positive electrode in the non-aqueous electrolyte secondary battery using the obtained positive electrode active material becomes large, so that the output of the battery becomes low. On the other hand, when the excess amount s of lithium exceeds 0.50, the initial discharge capacity when the positive electrode active material is used for the positive electrode of the battery decreases, and the reaction resistance of the positive electrode also increases.

In order to further reduce the reaction resistance, the excess amount s of lithium is preferably 0 or more, more preferably 0 or more and 0.35 or less, and 0 or more and 0.20 or less. Is even more preferable. When x, which indicates the nickel content in the above general formula, is 0.7 or less and y is 0.1 or more, the excess lithium amount s is 0.10 or more from the viewpoint of increasing the capacity. Is more preferable.

The value of y indicating the manganese content is 0.1 or more and 0.55 or less. When the value of y is in such a range, the transition metal composite hydroxide as a precursor is composed of a central portion composed of fine primary particles and an outer portion composed of primary particles larger than the fine primary particles outside the central portion. It has a structure with a shell. When the manganese content exceeds 0.55, there is a problem that the capacity of the battery used as the positive electrode active material decreases and the resistance increases.

Further, as represented by the above general formula, it is more preferable that the positive electrode active material of the present invention is adjusted so that the lithium transition metal composite oxide contains an additive element. By containing the above-mentioned additive element, it is possible to improve the durability characteristics and output characteristics of a battery using the additive element as a positive electrode active material.

In particular, when the additive element is uniformly distributed on the surface or inside of the particles, the above effect can be obtained for the entire particle, and the above effect can be obtained with a small amount of addition, and the decrease in volume can be suppressed.

Further, in order to obtain the effect with a smaller addition amount, it is preferable to increase the concentration of the additive element on the particle surface rather than inside the particle.

If the atomic ratio t of the additive element A to all the atoms exceeds 0.1, the metal elements that contribute to the Redox reaction decrease, which is not preferable because the battery capacity decreases. Therefore, the additive element M is adjusted so that the atomic ratio t is within the above range.

(Average particle size)
The positive electrode active material of the present invention has an average particle size of more than 1 μm and less than 15 μm, preferably more than 3 μm and less than 10 μm. When the average particle size is 1 μm or less, the tap density decreases, the packing density of the particles decreases when the positive electrode is formed, and the battery capacity per volume of the positive electrode decreases. On the other hand, when the average particle size exceeds 15 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 deteriorate.

Therefore, if the positive electrode active material of the present invention is adjusted to the above range, the battery capacity per volume can be increased in the battery using this positive electrode active material as the positive electrode, and high safety and high output can be achieved. Excellent battery characteristics can be obtained.

(Particle size distribution)
The positive electrode active material of the present invention has a highly homogeneous lithium having an index [(d90-d10) / average particle size] of 1.0 or less, preferably 0.70 or less, which is an index showing the spread of the particle size distribution. It is composed of secondary particles of transition metal composite oxide. When the particle size distribution is wide, the positive electrode active material contains many fine particles having a very small particle size with respect to the average particle size and coarse particles having a very large particle size with respect to the average particle size. Become. 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 reduces thermal stability and selectively deteriorates the fine particles. Therefore, the cycle characteristics deteriorate. On the other hand, when the positive electrode is formed by using the positive electrode active material in which many coarse 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.

Therefore, by setting the particle size distribution of the positive electrode active material to 1.0 or less in the index [(d90-d10) / average particle size], the proportion of fine particles and coarse particles can be reduced, and this positive electrode active material can be used. The battery used for the positive electrode has excellent safety, good cycle characteristics, and battery output. The average particle size, d90, and d10 are the same as those used for the composite hydroxide particles described above, and the measurement can be performed in the same manner.

(Tap density)
^{The positive electrode active material preferably has a tap density of 1.0 g / cm 3} or more, which is an index of packing density when tapped, and more preferably 1.3 g / cm ³ or more. For consumer and electric vehicles, increasing the capacity is a very important issue in order to extend the battery usage time and mileage, and not only increasing the capacity of the active material itself, but also increasing the amount of active material as an electrode. It is required to fill a lot. On the other hand, the electrode thickness of the secondary battery is about several tens of microns due to the problem of packing of the entire battery and the problem of electron conductivity. In particular, when the tap density is ^{less than 1.0 g / cm 3} , the amount of active material that can be put into the limited electrode volume decreases, and the capacity of the entire secondary battery cannot be increased. The upper limit of the tap density is not particularly limited, but the upper limit under normal manufacturing conditions is about ^{3.0 g / cm 3.}

(Characteristic)
When the positive electrode active material is used for the positive electrode of a 2032 type coin battery, for example, a high initial discharge capacity of 150 mAh / g or more, a low positive electrode resistance, and a high cycle capacity retention rate can be obtained, and a non-aqueous electrolyte secondary It exhibits excellent properties as a positive electrode active material for batteries.

Hereinafter, examples and comparative examples of the present invention will be described in detail.
(Example 1)
(Nucleation process)
First, the temperature in the tank was set to 40 ° C. while adding half the amount of water to the reaction tank having a capacity of 60 L and stirring the mixture. The inside of the reaction vessel at this time had an oxidizing atmosphere (oxygen concentration: 21% by volume). An appropriate amount of 20% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water is added to the water in the reaction tank to adjust the pH value of the reaction aqueous solution in the tank to 13.0 based on the liquid temperature of 25 ° C. did. Further, the ammonia concentration in the reaction aqueous solution was adjusted to 10 g / L.

Next, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in water to prepare a 2 mol / L mixed aqueous solution. In this mixed aqueous solution, the element molar ratio of each metal was adjusted to be Ni: Mn: Co = 33: 33: 33. This mixed aqueous solution was supplied to the reaction aqueous solution in the reaction vessel at a predetermined ratio. At the same time, 25% by mass aqueous ammonia and 20% by mass aqueous sodium hydroxide solution are also added to the reaction aqueous solution at a constant rate, and the pH of the reaction aqueous solution (nuclear generation aqueous solution) is maintained at the above values. While controlling the value to 13.0 (nucleation pH value), crystallization was carried out for a predetermined time to perform nucleation.

(Seed particle generation process)
After the completion of nucleation, 64% by mass sulfuric acid was added until the pH value of the reaction aqueous solution reached 11.6 based on the liquid temperature of 25 ° C. After the pH value of the reaction aqueous solution reached 11.6, the supply of the 20 mass% sodium hydroxide aqueous solution was restarted to the reaction aqueous solution (particle growth aqueous solution), and the pH value was adjusted based on the liquid temperature of 25 ° C. 11. While controlling to 6, crystallization was continued for 180 minutes to grow nuclei and generate seed particles. The centrifugal sedimentation density of the slurry containing the seed particles was 0.296 g / cm ³ .

(Particle growth process)
After that, the supply liquid was temporarily stopped, and nitrogen gas was circulated at 100 L / min until the oxygen concentration in the reaction tank space became 0.1% by volume or less. Then, the liquid supply was restarted, and crystallization was performed for 210 minutes. Then, the product was washed with water, filtered, and dried to obtain composite hydroxide particles.

(Heat treatment, firing process)
The obtained composite hydroxide is heat-treated at 150 ° C. for 12 hours, and then commercially available lithium carbonate is added so that the molar ratio (Li / M ratio) of metal to lithium is 1.2, and a shaker mixer device (Shaker mixer device). It was thoroughly mixed using TURBULA Type T2C manufactured by Willy e Bacoffen (WAB) to obtain a mixture. This mixture was fired in an air (oxygen: 21% by volume) air stream at 950 ° C. and further crushed to obtain a positive electrode active material for a non-aqueous electrolyte secondary battery.

(Example 2)
The precursor and the positive electrode active material were prepared in the same manner as in Example 1 except that the pH value and the ammonia concentration in the reaction aqueous solution were adjusted and the centrifugal sedimentation density of the slurry containing the seed particles ^{was controlled to 0.327 g / cm 3.} Obtained.

(Example 3)
The precursor and the positive electrode active material were prepared in the same manner as in Example 1 except that the pH value and the ammonia concentration in the reaction aqueous solution were adjusted and the centrifugal sedimentation density of the slurry containing the seed particles ^{was controlled to 0.341 g / cm 3.} Obtained.

(Example 4)
The pH value and the concentration of ammonia in the reaction solution was adjusted, except that centrifugal sedimentation density of the slurry containing the seed particles was controlled to 0.345 g / cm ³ is the precursor and the cathode active material in the same manner as in Example 1 Obtained.

(Example 5)
The precursor and the positive electrode active material were prepared in the same manner as in Example 1 except that the pH value and the ammonia concentration in the reaction aqueous solution were adjusted and the centrifugal sedimentation density of the slurry containing the seed particles ^{was controlled to 0.369 g / cm 3.} Obtained.

(Example 6)
The precursor and the positive electrode active material were prepared in the same manner as in Example 1 except that the pH value and the ammonia concentration in the reaction aqueous solution were adjusted and the centrifugal sedimentation density of the slurry containing the seed particles ^{was controlled to 0.384 g / cm 3.} Obtained.

(Comparative Example 1)
The precursor and the positive electrode active material were prepared in the same manner as in Example 1 except that the pH value and the ammonia concentration in the reaction aqueous solution were adjusted and the centrifugal sedimentation density of the slurry containing the seed particles ^{was controlled to 0.392 g / cm 3.} Obtained.

(Comparative Example 2)
The pH value and the concentration of ammonia in the reaction solution was adjusted, except that centrifugal sedimentation density of the slurry containing the seed particles was controlled to 0.423 g / cm ³ is the precursor and the cathode active material in the same manner as in Example 1 Obtained.

(Evaluation results of Examples and Comparative Examples)
A positive electrode active material was obtained using the composite hydroxide particles obtained in Examples and Comparative Examples as precursors. The positive electrode active material was produced by mixing composite hydroxide particles and lithium carbonate to form a lithium mixture, and then firing the mixture. Table 1 shows the centrifugal sedimentation density of the seed particles in Examples and Comparative Examples and the oil absorption of the obtained positive electrode active material. The lower the centrifugal sedimentation density, the higher the oil absorption. It is considered that the lower the centrifugal sedimentation density, the larger the number of primary particles, and therefore the smaller the outer shell growth per particle, the thinner the outer shell and the higher the oil absorption.

Claims (4)

General formula: Ni x Mn y Coz M t (OH) 2 + α (x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, 0 ≦ α ≦ 0.5, and M are additive elements, and one or more additive elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W. ), Which is a method for producing nickel-cobalt-manganese composite hydroxide particles, which is a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery.
The nucleation aqueous solution containing at least a metal compound containing nickel and a metal compound containing manganese and an ammonium ion feeder is controlled so that the pH value becomes 12.0 to 14.0 based on a liquid temperature of 25 ° C. A nucleation step in which nucleation is performed in an oxidizing atmosphere with an oxygen concentration of more than 1% by volume.
A metal compound containing at least nickel, a metal compound containing manganese, and an ammonium ion feeder are supplied to the aqueous solution for particle growth containing nuclei formed in the nucleation step, and the pH value at a liquid temperature of 25 ° C. is adjusted. A seed particle generation step in which seed particles are generated by controlling the pH value to be 10.5 to 12.0 and lower than the pH value in the nucleus generation step.
A metal compound containing at least nickel, a metal compound containing manganese, and an ammonium ion feeder are supplied to the particle growth slurry containing the seed particles formed in the seed particle generation step, and oxygen is generated from the oxidizing atmosphere. It is provided with a particle growth step of switching to a non-oxidizing atmosphere having a concentration of 1% by volume or less and growing the seed particles.
The centrifugal sedimentation density of the seed particles obtained by dividing the solid content density (g / L) of the slurry by the centrifuge sedimentation volume (cm 3 / L) of the slurry is controlled to 0.39 g / cm 3 or less. A method for producing a nickel-manganese composite hydroxide. The method for producing nickel-manganese composite hydroxide particles according to claim 1, wherein the time of the seed particle generation step is 40% or less of the total time of the seed particle generation step and the particle growth step. The method for producing nickel-manganese composite hydroxide particles according to claim 1 or 2, wherein the oxygen concentration in the oxidizing atmosphere is 10% by volume or more. The method for producing nickel-manganese composite hydroxide particles according to any one of claims 1 to 3, wherein the oxygen concentration in the non-oxidizing atmosphere is 0.5% by volume or less.

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