JP7114876B2 - Transition metal composite hydroxide particles and manufacturing method thereof, positive electrode active material for lithium ion secondary battery and manufacturing method thereof, and lithium ion secondary battery - Google Patents

Description

The present invention provides transition metal composite hydroxide particles, a method for producing the same, a positive electrode active material for a lithium ion secondary battery using the transition metal composite hydroxide particles as a precursor, a method for producing the same, and the lithium ion secondary The present invention relates to a lithium ion secondary battery using a positive electrode active material for batteries.

In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, there is a strong demand for the development of small, lightweight secondary batteries with high energy density. Also, there is a strong demand for the development of high-output secondary batteries as power sources for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and intercalating lithium is used as an active material for the negative electrode and the positive electrode. As the electrolyte, a non-aqueous electrolytic solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent, or a non-aqueous electrolyte such as a nonflammable solid electrolyte having ion conductivity is used.

Such lithium ion secondary batteries are currently being actively researched and developed. Since the ion secondary battery can obtain a high voltage of the 4V class, it is being put to practical use as a battery having a high energy density.

Lithium-transition metal composite oxides mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, and lithium-nickel composite oxide using nickel, which is cheaper than cobalt ( LiNiO ₂ ), lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ ) and the like have been proposed.

By the way, in order to obtain a lithium-ion secondary battery having excellent cycle characteristics and output characteristics, it is preferable that the positive electrode active material is composed of particles having a small particle size and a narrow particle size distribution. A positive electrode active material composed of small-diameter particles has a large specific surface area, and can sufficiently secure a reaction area with an electrolytic solution. In addition, since the positive electrode can be made thin by using particles with a small particle diameter, the distance that lithium ions move inside the positive electrode or between the positive electrode active material and the electrolyte solution is shortened, and the positive electrode resistance is reduced. On the other hand, by using particles with a narrow particle size distribution, the voltage applied to each particle in the electrode is made uniform, and the decrease in battery capacity due to selective deterioration of the particles is suppressed.

In order to further improve the output characteristics, it is effective to form a space into which the electrolytic solution can enter inside the positive electrode active material. A positive electrode active material having such a structure has a larger reaction area with an electrolytic solution than a positive electrode active material with a solid structure having a particle diameter of approximately the same size, so that the positive electrode resistance can be significantly reduced. . It is known that the positive electrode active material inherits the properties of the transition metal composite hydroxide particles that serve as its precursor. That is, in order to obtain a positive electrode active material with such excellent properties, it is necessary to appropriately control the particle size, particle size distribution, particle structure, etc. of the transition metal composite hydroxide particles that are the precursor. becomes.

Japanese Patent Application Laid-Open No. 2012-246199 discloses that the pH value of an aqueous solution for nucleation containing at least a metal compound containing a transition metal and an ammonium ion donor is controlled to be in the range of 12.0 to 14.0. , the nucleation step for generating nuclei, and the pH value of the aqueous solution for particle growth containing the generated nuclei is lower than the pH value of the nucleation step and is in the range of 10.5 to 12.0. a grain growth step in which growth is controlled and controlled, the reaction atmosphere in the nucleus growth step is made an oxidizing atmosphere, and the oxidizing is in the range of 0% to 30% with respect to the entire grain growth step time from the start of the grain growth step. A method for producing transition metal composite hydroxide particles is disclosed, characterized in that the atmosphere is switched to a non-oxidizing atmosphere having an oxygen concentration of 1% or less. According to this method, it has a small particle size and a narrow particle size distribution, and has a central portion made of fine primary particles, and has an outer shell portion made of plate-shaped primary particles larger than the fine primary particles outside the central portion. Transition metal composite hydroxide particles are obtained.

The positive electrode active material, which uses transition metal composite hydroxide particles as a precursor, has a small particle size, a narrow particle size distribution, and a hollow structure. can be improved, but the packing density may decrease, resulting in a decrease in battery capacity per unit volume. In addition, in the grain growth process, it is necessary to switch the reaction atmosphere from an oxidizing atmosphere to a non-oxidizing atmosphere. , it is necessary to temporarily stop the supply of the raw material aqueous solution, etc., and there is room for improvement in terms of productivity.

On the other hand, in JP-A-2015-164123, an aqueous solution of a nucleating metal salt containing at least cobalt and an aqueous solution containing an ammonium ion donor are mixed, and the pH value is in the range of 12.0 to 14.0. A nucleation step in which nucleation is performed in an oxidizing atmosphere with an oxygen concentration exceeding 10% by volume, and the pH value of the aqueous solution containing the generated nuclei is set to a range of 10.5 to 12.0. An aqueous metal salt solution for particle growth containing at least nickel and cobalt and an aqueous solution containing an ammonium ion donor are supplied, and the oxygen concentration is 0.5% by volume or less in a non-oxidizing atmosphere. a particle growth step for growing nuclei, the content of cobalt ions in the metal ions contained in the aqueous metal salt solution for nucleation is set to 70 mol% or more, and the amount of nuclei generated in the nucleation step is Nickel-cobalt composite hydroxide particles characterized by controlling the total amount of metal elements contained in the aqueous metal salt solution for particle growth supplied through the particle growth process to a range of 4.0 mol % to 11.0 mol %. A method of manufacture is disclosed.

According to this method, it is possible to obtain a positive electrode active material having a small particle size, a narrow particle size distribution, and an extremely small porosity of 2% or less inside the secondary particles. , the battery capacity per unit volume can be improved.

However, the production method described in JP-A-2015-164123 also requires switching the reaction atmosphere from an oxidizing atmosphere to a non-oxidizing atmosphere in the crystallization step, and there is room for improvement in terms of productivity. In addition, since the cobalt ion content in the aqueous metal salt solution for nucleation is higher than the cobalt ion content in the aqueous metal salt solution for the particle growth step, the production method described in JP-A-2015-164123 is used. The resulting composite hydroxide particles have a high cobalt content portion with a high cobalt concentration in the center of the secondary particles, and a portion with a low cobalt content around the high cobalt content portion. Although the cobalt in the cobalt-rich portion diffuses during firing, it is difficult to distribute it uniformly in the secondary particles of the obtained positive electrode active material. As a result, a heterogeneous phase containing a large amount of cobalt is formed, and the crystallinity is lowered, and cracks are likely to occur starting from the heterophase due to repeated charging and discharging, which may deteriorate the cycle characteristics.

JP 2012-246199 A JP 2015-164123 A

In view of the above problems, the present invention provides a positive electrode active material that can simultaneously improve battery capacity, output characteristics, and cycle characteristics when configuring a secondary battery, and a transition that is a precursor thereof. It is an object of the present invention to provide metal composite hydroxide particles and to enable efficient production of these positive electrode active materials and transition metal composite hydroxide particles in industrial-scale production.

In the method for producing transition metal composite hydroxide particles of the present invention, a raw material aqueous solution containing at least a transition metal and an aqueous solution containing ammonium ions are supplied to a reaction vessel to form a reaction aqueous solution, followed by a crystallization reaction. A method for producing transition metal composite hydroxide particles as a precursor of a positive electrode active material for lithium ion secondary batteries by
A nucleation step of adjusting the pH value of the reaction aqueous solution in the range of 12.0 to 14.0 at a liquid temperature of 25 ° C. to generate nuclei;
The pH value of the reaction aqueous solution containing the nuclei obtained in the nucleation step at a liquid temperature of 25 ° C. is lower than the pH value in the nucleation step and is in the range of 10.5 to 12.0. a particle growth step of growing the nucleus under control of
Through the nucleation step and the particle growth step, an inert gas is blown into the reaction vessel at a flow rate of 0.2 L / min to 0.7 L / min per 1 L of the internal volume of the reaction vessel, and the nucleation step and the particles The reaction atmosphere in the growth step is a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less,
It is characterized by

The transition metal composite hydroxide particles of the present invention have the general formula (A): NixCoyMnzMt(OH) _2+a (where _x + _y + _z + _t =1, 0.3≤x≤0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ t ≤ 0.1, and 0 ≤ a ≤ 0.5, and M is Mg, Ca, Al, Ti, V, Cr, One or more additive elements selected from the group of Zr, Nb, Mo, Hf, Ta and W), transition metal composite hydroxide consisting of secondary particles formed by aggregation of a plurality of primary particles The secondary particles have an average particle size MV in the range of 2.0 μm to 3.0 μm, and an index indicating the spread of the particle size distribution [(d90−d10)/average particle size MV] is 0.45 or less, and the tap density is in the range of 1.2 g/cm ³ to 2.0 g/cm ³ ,
It is characterized by

In the transition metal composite hydroxide particles of the present invention, the secondary particles comprise solid particles formed by agglomeration of the plate-like primary particles, a central portion formed by agglomeration of the fine primary particles, and , and a two-layer particle composed of an outer shell portion formed by aggregation of the plate-like primary particles outside the center portion, and the existence ratio of the solid particles and the two-layer particles is It is preferably in the range of 1:9 to 9:1.

The method for producing the positive electrode active material for lithium ion secondary batteries of the present invention comprises:
a mixing step of mixing the transition metal composite hydroxide particles of the present invention with a lithium compound to form a lithium mixture;
a firing step of firing the lithium mixture at a temperature in the range of 650° C. to 980° C. in an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume;
characterized by comprising

The positive electrode active material for lithium ion secondary batteries of the present invention has the general formula (B): Li _1+u Ni _x Co _y Mn _z M _t O ₂ (−0.05≦u≦0.50, x+y+z+t=1, 0. 3≤x≤0.95, 0.05≤y≤0.55, 0≤z≤0.4, 0≤t≤0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta and W) and made of hexagonal lithium-transition metal composite oxide particles having a layered structure for a lithium ion secondary battery. The active material is composed of secondary particles formed by agglomeration of primary particles, and the secondary particles have an average particle size MV in the range of 2.0 μm to 4.0 μm and exhibit a broad particle size distribution. The index [(d90-d10)/average particle size MV] is 0.50 or less, the tap density is in the range of 1.2 g/cm ³ to 2.0 g/cm ³ , and the X-ray diffraction The crystallite diameter determined by the Scherrer formula from the (003) plane peak in is in the range of 1000 Å to 1400 Å,
It is characterized by

In the positive electrode active material for a lithium ion secondary battery of the present invention, solid secondary particles having a solid structure formed by aggregating a plurality of primary particles, and particles formed by aggregating a plurality of primary particles, and It consists of secondary particles composed of hollow secondary particles having a hollow structure having a hollow inside, and the existence ratio of the solid secondary particles and the hollow secondary particles is 1: 9 to 9: 1. A range is preferred.

A lithium ion secondary battery of the present invention comprises a positive electrode, a negative electrode, and an electrolyte, and is characterized in that the positive electrode active material for a lithium ion secondary battery of the present invention is used as a positive electrode material for the positive electrode. .

The secondary particles constituting the positive electrode active material of the present invention have an average particle size MV in the range of 2.0 μm to 4.0 μm, which is small, but has an extremely sharp particle size distribution and high crystallinity. In addition, it has a high tap density because it has a fine grain structure. When a lithium ion secondary battery is constructed using the positive electrode active material of the present invention having such particle characteristics as a positive electrode material, the battery capacity, output characteristics, and cycle characteristics can be improved at the same time. play.

Further, according to the present invention, it is possible to provide transition metal composite hydroxide particles, which are precursors thereof, having a particle structure that brings such particle properties to the positive electrode active material. Furthermore, according to the present invention, it becomes possible to efficiently produce these positive electrode active materials and transition metal composite hydroxide particles on an industrial scale.

Therefore, the present invention provides a lithium-ion secondary battery with excellent battery characteristics at low cost. Therefore, the industrial significance of the present invention is extremely large.

1 is a cross-sectional SEM image of the positive electrode active material obtained in Example 1. FIG. 2 is a cross-sectional SEM image of the positive electrode active material obtained in Comparative Example 1. FIG. 3 is a cross-sectional SEM image of the positive electrode active material obtained in Comparative Example 3. FIG. FIG. 4 is a schematic cross-sectional view of a 2032-type coin battery used for battery evaluation.

The present inventors have found a positive electrode active material for lithium ion secondary batteries (hereinafter referred to as "positive electrode active material") that can simultaneously improve battery capacity, output characteristics and cycle characteristics when used as a positive electrode material for lithium ion secondary batteries. ”) was earnestly examined.

In order to obtain a lithium-ion secondary battery with excellent cycle characteristics and output characteristics, the positive electrode active material needs to be composed of particles with a small particle size and a narrow particle size distribution. In particular, from the viewpoint of increasing the output, it is required that the average particle size MV of the secondary particles constituting the positive electrode active material be in the range of 2.0 μm to 4.0 μm. However, when the secondary particles have a particle size as small as this level, there is a problem that a sufficiently sharp particle size distribution and a tap density required for high output cannot be obtained in industrial-level operations.

Therefore, the present inventors have found that in a positive electrode active material having a small particle size in which the average particle size MV of the secondary particles is in the range of 2.0 μm to 4.0 μm, the particle size distribution is sufficiently narrow and the crystallinity is high. Furthermore, the inventors have considered that the desired battery characteristics of the lithium ion secondary battery can be obtained by configuring the secondary particles with dense secondary particles.

That is, the positive electrode active material is composed of secondary particles formed by aggregation of primary particles, and the secondary particles have an average particle size MV in the range of 2.0 μm to 4.0 μm, and the particle size distribution spreads. [(d90-d10)/average particle size MV], which is an index to show, is 0.50 or less, the tap density is 1.2 g/cm ³ to 2.0 g/cm ³ It has been found that these problems can be solved simultaneously by setting the crystallite diameter determined by the Scherrer formula from the (003) plane peak to 1000 Å to 1400 Å.

Furthermore, the present inventors investigated a method for producing transition metal composite hydroxide particles (hereinafter referred to as "composite hydroxide particles"), which is a precursor for obtaining a positive electrode active material having such a structure. . As a result, through the nucleation step and the particle growth step, an inert gas was blown into the reaction vessel at a flow rate of 0.2 L / min to 0.7 L / min per 1 L of the internal volume of the reaction vessel. Through the growth process, the reaction atmosphere is strictly regulated to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. It was found that composite hydroxide particles composed of particles can be obtained.

The present invention has been completed based on these findings.

1. Transition metal composite hydroxide particles 1-1. Transition Metal Composite Hydroxide Particles The composite hydroxide particles of the present invention have the general formula (A): _NixCoyMnzMt (OH) _2+a (where _x +y+ _z + _t =1, 0.3≦x≦0.3). 95, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, and 0≦a≦0.5, and M is Mg, Ca, Al, Ti , V, Cr, Zr, Nb, Mo, Hf, Ta and W), and consist of secondary particles formed by agglomeration of a plurality of primary particles characterized by In addition, the average particle diameter MV of the secondary particles of the composite hydroxide particles is in the range of 2.0 μm to 3.0 μm, which is an index showing the spread of the particle size distribution [(d90-d10) / average particle diameter MV] is 0.45 or less, and the tap density is in the range of 1.2 g/cm ³ to 2.0 g/cm ³ .

(1) Composition The composite hydroxide particles of the present invention have the general formula (A): Ni _x Co _{y Mnz} M _t (OH) _{2 + a} (where x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0 .05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, and 0≦a≦0.5, and M is Mg, Ca, Al, Ti, V, one or more additional elements selected from the group consisting of Cr, Zr, Nb, Mo, Hf, Ta and W). When a positive electrode active material is obtained using the composite hydroxide particles of the present invention as a raw material, the composition of the composite hydroxide particles is basically maintained in the resulting positive electrode active material. Therefore, the composition ratio of the composite hydroxide particles of the present invention is adjusted so as to be similar to the composition ratio required for the positive electrode active material to be obtained. However, it is necessary to consider the amount of elements that are inevitably incorporated in the manufacturing process of the composite hydroxide particles and the manufacturing process of the positive electrode active material, and the amount of the elements that are added in the manufacturing process of the positive electrode active material. Note that the contents of nickel (Ni), cobalt (Co), manganese (Mn), and the additional element M and their critical significance are the same as those of the positive electrode active material described later, so descriptions thereof are omitted here.

(2) Particle Structure The composite hydroxide particles of the present invention are composed of secondary particles formed by aggregation of a plurality of primary particles. Here, the term "substantially spherical secondary particles" refers to secondary particles in the form of rounded lumps such as spherical or elliptical spheres, and includes secondary particles having fine irregularities on the surface thereof.

In the present invention, it is sufficient that secondary particles having a highly dense particle structure are obtained in the finally obtained positive electrode active material. There is no particular limitation as long as the particles are highly cohesive.

The secondary particles can be composed of solid particles formed by aggregation of plate-like primary particles. Alternatively, the two are composed of a central portion formed by aggregating fine primary particles smaller than the plate-like primary particles, and an outer shell portion formed by aggregating the plate-like primary particles outside the central portion. It can also consist of layer particles. It is also within the scope of the present invention that these solid particles and bilayer particles are mixed.

When adopting a suitable configuration in which solid particles and two-layer particles are mixed, the ratio of the solid particles and the two-layer particles is preferably in the range of 1:9 to 9:1, preferably 2:8 to 8. :2, more preferably 3:7 to 7:3. Since this existence ratio and its critical significance are the same as those of the positive electrode active material described later, description thereof will be omitted here.

The plate-like primary particles preferably have an average particle size MV of 0.3 μm to 3 μm, and the fine primary particles preferably have an average particle size MV of 0.01 μm to 0.3 μm.

In bilayer particles, the average ratio of the outer diameter of the central portion to the particle size is preferably in the range of 10% to 50%, more preferably in the range of 20% to 40%, and more preferably in the range of 25% to 35%. % range is more preferred. When the average ratio of the outer diameter of the central portion to the particle size exceeds 50%, the hollow portion of the hollow secondary particles becomes too large in the obtained positive electrode active material, so that the positive electrode active material when filled as a positive electrode material. The occupied proportion becomes too small, and a sufficient charge/discharge capacity of the secondary battery cannot be ensured. On the other hand, if the average ratio of the outer diameter of the central portion to the particle size is less than 10%, the effect of reducing the reaction resistance due to the contact between the inner wall of the hollow portion and the electrolytic solution is not sufficiently large, so the internal resistance of the secondary battery is reduced. I can't.

Here, the average ratio of the outer diameter of the central part to the particle size of the bilayer particles is obtained by observing the cross section of the composite hydroxide particles with a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM). can be obtained by

Specifically, first, the cross section of the two-layer particle is observed in a field of view that allows the central portion and the outer shell portion of the two-layer particle among the secondary particles to be distinguished. The maximum length between any two points on the outer edge of the bilayer particle and the maximum length between any two points on the outer edge of the central part are measured, and these values are used as the particle size and the center of the bilayer particle, respectively. outside diameter of the part. By dividing the outer diameter of the central portion by the particle size of the two-layer particles, the ratio of the outer diameter of the central portion to the particle size of the two-layer particles is obtained. By performing the same measurement on 10 or more bilayer particles and calculating the number average value, the average ratio of the outer diameter of the central part to the particle size of the bilayer particles in the entire sample is finally calculated. decide.

(3) Average particle size MV of secondary particles
In the composite hydroxide particles of the present invention, the average particle size MV of the secondary particles is adjusted to 2.0 μm to 4.0 μm, preferably 2.4 μm to 3.6 μm, more preferably 2.5 μm to 3.5 μm. be done. The average particle size MV of the secondary particles correlates with the average particle size MV of the positive electrode active material using this composite hydroxide as a precursor. Therefore, by controlling the average particle size MV of the secondary particles in such a range, the average particle size MV of the positive electrode active material having the composite hydroxide particles as a precursor is controlled in a desired range, and the positive electrode It becomes possible to realize a further increase in output of the active material.

In the present invention, the mean particle size MV of the secondary particles means the volume-based mean particle size (Mean Volume Diameter). can be done.

(4) Particle size distribution In the composite hydroxide particles of the present invention, [(d90-d10)/average particle size MV], which is an index showing the spread of the particle size distribution, is 0.50 or less, preferably 0.48 or less. More preferably, it is adjusted to be 0.45 or less.

The particle size distribution of the positive electrode active material is strongly influenced by the particle size distribution of its precursor, the composite hydroxide particles. Therefore, when composite hydroxide particles containing many fine particles and coarse particles are used as a precursor, the obtained positive electrode active material also contains many fine particles and coarse particles. Safety, cycle characteristics and output characteristics cannot be sufficiently improved. On the other hand, if the [(d90-d10)/average particle diameter MV] of the composite hydroxide particles is adjusted to 0.50 or less, the particle size distribution of the positive electrode active material using this as a precursor can be narrowed, but in order to meet the recent demand for battery characteristics, even if the positive electrode active material has a small particle size with an average particle size MV in the range of 2 μm to 4 μm, [(d90-d10 )/average particle size MV] must be 0.50 or less. However, assuming industrial-scale production, as the composite hydroxide particles, [(d90-d10) / average particle diameter MV] is excessively small, that is, the particle size distribution is extremely sharp. is not realistic considering the product yield and process costs. Therefore, the lower limit of [(d90-d10)/average particle diameter MV] is preferably about 0.25.

Note that d10 is the particle size where the volume of individual particles is accumulated from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles (the cumulative curve of the particle size distribution with the total volume as 100%) d90 means the particle diameter at which the cumulative curve reaches 10%, and d90 means the particle diameter at which the cumulative curve reaches 90%. These values can be obtained from volume integrated values measured with a laser beam diffraction/scattering particle size analyzer.

1-2. Method for Producing Transition Metal Composite Hydroxide Particles In the method for producing composite hydroxide particles of the present invention, a raw material aqueous solution containing at least a transition metal and an aqueous solution containing ammonium ions are supplied into a reaction vessel to react. An aqueous solution is formed, and transition metal composite hydroxide particles are obtained by a crystallization reaction.

In the method for producing composite hydroxide particles of the present invention, the crystallization reaction is performed by adjusting the pH value of the reaction aqueous solution at a liquid temperature of 25° C. to a range of 12.0 to 14.0 to generate nuclei. The pH value of the reaction aqueous solution containing nuclei obtained in the step and the nucleation step is lower than the pH value in the nucleation step and in the range of 10.5 to 12.0 at a liquid temperature of 25 ° C. It is characterized by clearly distinguishing between two stages, namely, a particle growth process in which the nuclei are grown under control of the nuclei.

In particular, in the present invention, through the nucleation step and the particle growth step, an inert gas is blown into the reaction vessel at a flow rate of 0.2 L / min to 0.7 L / min per 1 L of the internal volume of the reaction vessel, and the nucleation step and the reaction atmosphere in the grain growth step is strictly regulated to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. Conventionally, the reaction atmosphere in the nucleation step and the grain growth step is basically a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, and part of the nucleation step and/or the grain growth step However, in the present invention, the reaction atmosphere is set to an oxygen concentration of 2 in the entire process from the start of the nucleation step to the end of the grain growth step. It is strictly regulated so that the non-oxidizing atmosphere is less than the volume %. Conventionally, when the reaction atmosphere is regulated to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, for example, an inert gas is blown into the reaction layer and then the reaction vessel is sealed. As the size of the device increases, the equipment cost for strictly maintaining the sealed state becomes excessive. Therefore, the conventional means cannot strictly control the reaction atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. In the present invention, an inert gas is continuously blown into the reaction vessel at a flow rate of 0.2 L / min to 0.7 L / min per 1 L of the internal volume of the reaction vessel, so that the reaction atmosphere has an oxygen concentration of 2% by volume or less. It is different from conventional means in that it is strictly regulated so that the atmosphere is non-oxidizing.

The method for producing composite hydroxide particles of the present invention is not limited by its composition as long as the structure, volume average particle diameter MV and particle size distribution described above can be realized. It can be suitably applied to the composite hydroxide particles to be processed.

(1) Crystallization reaction In the method for producing composite hydroxide particles of the present invention, the crystallization reaction is clearly separated into two stages: a nucleation step in which nuclei are mainly generated, and a particle growth step in which particles are mainly grown. . In addition, the crystallization conditions in each step should be adjusted, in particular, the reaction atmosphere should be a non-oxidizing atmosphere, and the amount of inert gas to be blown into the reaction vessel to create a non-oxidizing atmosphere should be adjusted to 0.00 per 1 L of the volume of the reaction vessel. By making it equivalent to 2 to 0.7 L/min, it is possible to obtain composite hydroxide particles having the above-described volume average particle size MV and particle size distribution. In addition, since the operations required for adjusting the crystallization conditions are basically the same as in the prior art, the method for producing composite hydroxide particles of the present invention can be easily applied to industrial-scale production. .

[Nucleation step]
In the nucleation step, first, an inert gas is blown into the reaction vessel at a flow rate equivalent to 0.2 to 0.7 L / min with respect to 1 L of the reaction vessel volume, and the atmosphere in the reaction vessel is adjusted to an oxygen concentration of 2% by volume. The following non-oxidizing atmosphere is adjusted, and an alkaline aqueous solution and an aqueous solution containing an ammonium ion donor are supplied and mixed in the reaction vessel, and the pH value at a liquid temperature of 25 ° C. is 12.0 to 14.0. , to prepare a pre-reaction aqueous solution having an ammonium ion concentration of 3 g/L to 25 g/L. The pH value of the pre-reaction aqueous solution can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

At the same time, a raw material aqueous solution is prepared by dissolving a transition metal compound as a raw material in the nucleation step in water. In addition, in the method for producing composite hydroxide particles of the present invention, the composition ratio of each transition metal in the obtained composite hydroxide particles substantially matches the composition ratio of each transition metal in the raw material aqueous solution. Therefore, the composition ratio of the transition metals in the raw material aqueous solution is adjusted so as to be the same as the composition ratio required for the composite hydroxide particles to be obtained.

Next, while stirring the pre-reaction aqueous solution, the raw material aqueous solution is supplied. As a result, an aqueous solution for nucleation, which is a reaction aqueous solution in the nucleation step, is formed in the reaction tank. Since the pH value of this aqueous solution for nucleation is within the range described above, the growth of nuclei is suppressed in the nucleation step, and the generation of nuclei occurs preferentially. However, the growth reaction of the nucleus also occurs partially. In the nucleation step, the pH value and the ammonium ion concentration of the aqueous solution for nucleation change along with the nucleation. For this reason, an appropriate amount of an alkaline aqueous solution and an ammonia aqueous solution are continuously supplied, and the pH value of the aqueous solution for nucleation at a liquid temperature of 25 ° C. is in the range of 12.0 to 14.0, and the ammonium ion concentration is 3 g / L to 25 g. It is necessary to control so as to keep it within the range of /L.

In such a nucleation step, new nuclei are continuously generated by supplying an aqueous solution containing a starting metal salt aqueous solution, an alkaline aqueous solution and an ammonium ion donor to the nucleating aqueous solution. Then, when the target amount of nuclei is generated in the nucleation aqueous solution, the nucleation step is terminated. At this time, the amount of nuclei generated can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the nucleation aqueous solution.

The amount of nuclei generated in the nucleation step is not particularly limited. However, in order to obtain composite hydroxide particles with a narrow particle size distribution, the amount of nuclei generated with respect to the metal element in the metal compound supplied through the nucleation step and the particle growth step should be 0.1 atomic % to 2 atomic %. and more preferably 0.1 atomic % to 1.5 atomic %.

[Particle growth step]
After the nucleation step is completed, the pH value of the aqueous solution for nucleation after nucleation is adjusted so that the pH value is in the range of 10.5 to 12.0 based on the liquid temperature of 25 ° C., and the ammonium ion concentration is By maintaining the concentration in the range of 3 g/L to 25 g/L, an aqueous solution for particle growth, which is the reaction aqueous solution in the particle growth step, is formed. At this time, the pH value of the aqueous solution for particle growth can be adjusted only by stopping the supply of the alkaline aqueous solution. It is preferable to adjust the pH value after stopping the supply. In this case, the pH value is adjusted by adding an inorganic acid of the same kind as the acid that constitutes the metal compound as a raw material, for example, sulfuric acid when sulfate is used as a raw material, to the aqueous solution for nucleation, and stirring the inside of the reaction vessel. It can be done by supplying while

Next, while continuing to blow inert gas into the reaction tank to maintain the atmosphere in the reaction tank in a non-oxidizing atmosphere, while stirring the aqueous solution for particle growth, the raw material aqueous solution and the aqueous ammonia solution are supplied. to resume. At this time, since the pH value of the aqueous solution for particle growth is within the range described above, almost no new nuclei are formed, nuclei (particles) grow, and composite hydroxide particles having a predetermined particle size are formed. be. However, even in the particle growth process, the pH value and ammonium ion concentration of the aqueous solution for particle growth change as the particles grow. It is necessary to maintain the ion concentration within the above range. In addition, in order to maintain the atmosphere in the reaction vessel as a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less, following the nucleation step, inert gas was added to the reaction vessel in an amount of 0.05 to 1 L of the volume of the reaction vessel. It is introduced at a flow rate equivalent to 2 L/min to 0.7 L/min.

(2) Supply aqueous solution [raw material aqueous solution]
In the method for producing composite hydroxide particles of the present invention, the composition ratio of the metal elements in the obtained composite hydroxide particles substantially matches the composition ratio of the metal elements in the raw material aqueous solution. Therefore, it is necessary to appropriately adjust the content of the metal element in the raw material aqueous solution according to the desired composition of the composite hydroxide particles. For example, when trying to obtain the composite hydroxide particles represented by the general formula (A) described above, the ratio of the metal elements in the raw metal salt aqueous solution is Ni: Co: Mn : M=x: y: z : t (However, x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ t ≤ 0.1) It is necessary to

As the source of the transition metal element, it is preferable to use a water-soluble metal compound, specifically sulfate, nitrate, chloride, etc. From the viewpoint of cost and prevention of halogen contamination, sulfate is preferably used. is particularly preferred.

In addition, the composite hydroxide contains an additive element M (M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) In this case, it is preferable to use a water-soluble metal compound, specifically sulfate, nitrate, chloride, etc., as the supply source of the additive element M, similarly to the supply source of the transition metal element. More specifically, for example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate , ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate, ammonium tungstate and the like can be preferably used.

The total concentration of the raw material aqueous solution is adjusted to preferably 1.0 mol/L to 2.6 mol/L, more preferably 1.5 mol/L to 2.2 mol/L, in terms of the total amount of metal compounds. If the concentration of the raw material aqueous solution is less than 1.0 mol/L, the amount of crystallized material per reaction tank is small, resulting in low productivity. On the other hand, when the concentration of the mixed aqueous solution exceeds 2.6 mol/L, it exceeds the saturation concentration at room temperature, and crystals of each metal compound re-precipitate especially at low temperature, which may clog pipes.

Note that the metal compound described above does not necessarily have to be supplied to the reaction vessel as the raw salt solution. For example, when using a metal compound that, when mixed, reacts in the raw material aqueous solution to produce a compound other than the target compound, separate Alternatively, an aqueous metal compound solution may be prepared in the above step and supplied to the reaction vessel at a predetermined ratio as individual aqueous metal compound solutions.

The amount of the raw material aqueous solution supplied is such that the concentration of the composite metal hydroxide in the reaction solution at the end of the particle growth step is preferably 30 g/L to 200 g/L, more preferably 80 g/L to 150 g/L. so that If the concentration of the composite metal hydroxide is less than 30 g/L, aggregation of primary particles may be insufficient. On the other hand, when it exceeds 200 g/L, the reaction aqueous solution is not sufficiently stirred in the reaction tank, and the aggregation conditions become non-uniform, which may cause uneven particle growth.

[Aqueous alkaline solution]
The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkaline metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. Although the alkali metal hydroxide can be directly added to the reaction aqueous solution in a solid state, it is preferably added as an aqueous solution from the viewpoint of ease of pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% to 50% by mass, more preferably 20% to 30% by mass. By adjusting the concentration of the alkali metal aqueous solution to such a range, the pH value is locally increased at the addition position in the reaction tank while suppressing the amount of solvent supplied to the reaction system, that is, the amount of water. can be prevented, and composite hydroxide particles with a narrow particle size distribution can be efficiently obtained.

The method of supplying the alkaline aqueous solution is not particularly limited as long as the pH value of the reaction aqueous solution does not become locally high and is maintained within a predetermined range. For example, while sufficiently stirring the reaction aqueous solution, it may be supplied by a pump capable of controlling the flow rate such as a metering pump.

[Aqueous solution containing ammonium ion donor]
The aqueous solution containing an ammonium ion donor is not particularly limited as long as it can supply ammonium ions in the reaction aqueous solution. Aqueous solutions can be used.

When aqueous ammonia is used as the ammonium ion donor, its concentration is preferably 20% to 30% by mass, more preferably 22% to 28% by mass. By controlling the concentration of ammonia water within such a range, the loss of ammonia due to volatilization can be minimized, and production efficiency can be improved.

The aqueous solution containing the ammonium ion donor can also be supplied by a pump whose flow rate can be controlled in the same manner as the alkaline aqueous solution.

(3) pH value In the method for producing composite hydroxide particles of the present invention, the pH value at a liquid temperature of 25° C. is in the range of 12.0 to 14.0 in the nucleation step, and in the particle growth step. Control within the range of 10.5 to 12.0 is required. In any step, the fluctuation range of the pH value during the crystallization reaction is preferably within ±0.2. If the fluctuation range of the pH value is large, the ratio of the amount of nucleation and particle growth will not be constant, making it difficult to obtain composite hydroxide particles with a narrow particle size distribution.

[Nucleation step]
In the nucleation step, the pH value of the reaction aqueous solution, that is, the aqueous solution for nucleation, is 12.0 to 14.0, preferably 12.3 to 13.5, more preferably 12.5 at a liquid temperature of 25 ° C. It is necessary to adjust to the range of ~13.3. As a result, it is possible to give priority to nucleation while suppressing the growth of nuclei, so that the nuclei generated in the nucleation step can be homogeneous and have a narrow particle size distribution. If the pH value is less than 12.0, not only nucleation but also nuclei (particles) tend to grow, so that the composite hydroxide particles to be obtained have non-uniform particle diameters and deteriorate in particle size distribution. On the other hand, when the pH value exceeds 14.0, the generated nuclei become too fine, which causes a problem of gelation of the aqueous solution for nucleation. However, even when the pH value of the aqueous solution for nucleation is within the range described above, the growth of nuclei (particles) occurs to some extent.

[Particle growth step]
In the particle growth step, the pH value of the reaction aqueous solution, that is, the aqueous solution for particle growth, is lower than the pH value in the nucleation step and is 10.5 to 12.0, preferably 11, at a liquid temperature of 25°C. .0 to 12.0, more preferably 11.5 to 12.0. As a result, the generation of new nuclei is suppressed, it becomes possible to give priority to particle growth, and the resulting composite hydroxide particles can be made homogeneous and have a narrow particle size distribution. On the other hand, if the pH is less than 10.5, the concentration of ammonium ions increases and the solubility of metal ions increases, which not only slows down the crystallization reaction but also increases the amount of metal ions remaining in the aqueous reaction solution. , productivity deteriorates. On the other hand, if the pH value exceeds 12.0, the amount of nuclei generated during the particle growth process increases, the particle size of the resulting composite hydroxide particles becomes non-uniform, and the particle size distribution deteriorates.

When the pH value is 12.0, it is a boundary condition between nucleation and nucleus growth, so depending on the presence or absence of nuclei in the reaction aqueous solution, the condition may be either the nucleation step or the particle growth step. can be done. That is, when the pH value of the nucleation step is set higher than 12.0 to generate a large amount of nuclei, and then the pH value of the particle growth step is set to 12.0, a large amount of nuclei are present in the reaction aqueous solution, resulting in particles Growth occurs preferentially, and composite hydroxide particles with a narrow particle size distribution can be obtained. On the other hand, when the pH value of the nucleation step is set to 12.0, since there are no growing nuclei in the reaction aqueous solution, nucleation occurs preferentially. , the generated nuclei grow and good composite hydroxide particles can be obtained. In any case, the pH value in the grain growth step should be controlled at a value lower than the pH value in the nucleation step. It is preferably 0.5 or more lower than the pH value of the production step, more preferably 1.0 or more lower.

(4) Reaction Atmosphere In the method for producing composite hydroxide particles of the present invention, control of the reaction atmosphere is of great significance as well as control of the pH value in each step. That is, the pH value in each process is controlled, and an inert gas is supplied to the reaction vessel at a rate of 0.2 L/min to 0.7 L/min per 1 L of the internal volume of the reaction vessel throughout the nucleation process and the particle growth process. The tap density and crystallite diameter of the composite hydroxide particles obtained by blowing in at a flow rate and strictly regulating the reaction atmosphere in the nucleation step and the particle growth step to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less can be controlled within an appropriate range.

[Non-oxidizing atmosphere]
In the method for producing composite hydroxide particles of the present invention, it is necessary to control the reaction atmosphere to a non-oxidizing atmosphere throughout the nucleation step and particle growth step. Specifically, the oxygen concentration in the reaction atmosphere is controlled to 2% by volume or less, preferably 1% by volume or less, more preferably 0.6% by volume or less. When the oxygen concentration in the reaction atmosphere exceeds 2% by volume, the excessively fine primary particles aggregate in an irregular shape to form secondary particles, so that the crystallinity of the resulting composite hydroxide particles is lost. problems such as In the present invention, the lower limit of the oxygen concentration in the reaction atmosphere is not limited as long as the flow rate of the inert gas described below is an appropriate value. However, the oxygen concentration in the reaction atmosphere is preferably 0.3% by volume or more, more preferably 0.4% by volume or more.

[Inert gas and its flow rate]
As the inert gas, for example, argon gas, carbon dioxide gas, nitrogen gas, or the like can be used, but it is particularly preferable to use nitrogen gas, which is inexpensive and easy to handle.

In the method for producing composite hydroxide particles of the present invention, an inert gas is introduced into the reaction vessel at a rate of 0.2 L/min to 0.7 L/min, preferably 0.2 L/min to 0.7 L/min per 1 L of the internal volume of the reaction vessel, through the nucleation step and the particle growth step. is blown at a flow rate of 0.3 L/min to 0.6 L/min, more preferably 0.4 L/min to 0.5 L/min, so that the reaction atmosphere in the nucleation step and the particle growth step is a non-oxidizing atmosphere. . If the flow rate of the inert gas is less than 0.2 L/min, the atmosphere in the reaction vessel cannot be made into a non-oxidizing atmosphere, and the tap density and crystallite size of the resulting composite hydroxide particles are reduced. In a positive electrode active material formed using composite hydroxide particles as a precursor, it is not possible to achieve a sufficiently dense particle structure while having a small particle size. When a secondary battery is constructed by using such a positive electrode active material having a small particle size but not a high density as a positive electrode material, there arises a problem that the packing density is lowered and the capacity per volume is lowered. On the other hand, when the flow rate of the inert gas exceeds 0.7 L/min, the resulting composite hydroxide particles become too dense, and the volume average particle diameter MV becomes as small as less than 2.0 μm, resulting in handling of the particles. becomes difficult. In a structure in which solid particles and double-layered particles are mixed, since the hollow part completely disappears inside all the particles, the reaction area with the electrolytic solution becomes smaller, the positive electrode resistance increases, and the output characteristics deteriorate. trend.

The method of supplying the inert gas into the reaction vessel is either a method of supplying to a space in the reaction vessel that is in contact with the reaction aqueous solution, or a method of supplying directly into the reaction aqueous solution using an air diffuser or the like. But it is possible.

(5) Ammonium ion concentration The ammonium ion concentration in the reaction aqueous solution is preferably maintained in the range of 3 g/L to 25 g/L, more preferably 5 g/L to 20 g/L throughout the nucleation step and particle growth step. Is required. Since ammonium ions function as a complexing agent in the reaction aqueous solution, if the ammonium ion concentration is less than 3 g/L, the solubility of the metal ions cannot be kept constant, and the reaction aqueous solution tends to gel, causing the shape and shape to change. It becomes difficult to obtain composite hydroxide particles with a uniform particle size. On the other hand, when the ammonium ion concentration exceeds 25 g/L, the solubility of the metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, causing compositional deviation and the like.

If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ions fluctuates and uniform composite hydroxide particles are no longer formed. For this reason, it is preferable to control the fluctuation width of the ammonium ion concentration within a certain range through the nucleation step and the grain growth step, and specifically, it is preferable to control the fluctuation width within ±5 g/L.

(6) Reaction temperature The temperature of the reaction aqueous solution (reaction temperature) must be controlled in the range of preferably 20°C or higher, more preferably 20°C to 60°C throughout the nucleation step and particle growth step. If the reaction temperature is lower than 20° C., the solubility of the reaction aqueous solution becomes low, and nucleation tends to occur, making it difficult to control the volume average particle diameter MV and particle size distribution of the resulting composite hydroxide particles. Become. The upper limit of the reaction temperature is not particularly limited, but if it exceeds 60° C., volatilization of ammonia is accelerated, and an ammonium ion supplier is supplied to control the ammonium ions in the reaction aqueous solution within a certain range. The amount of the aqueous solution containing is increased, and the production cost is increased.

(7) Production Apparatus In the method for producing composite hydroxide particles of the present invention, it is preferable to use an apparatus such as a batch reaction tank in which the product is not recovered until the reaction is completed. With such an apparatus, composite hydroxide particles with a narrow particle size distribution are not recovered at the same time as the growing particles, unlike a continuous crystallizer that recovers the product by an overflow method. can be easily obtained.

In addition, in the method for producing composite hydroxide particles of the present invention, it is necessary to strictly control the reaction atmosphere during the crystallization reaction. preferable. With such an apparatus, the reaction atmosphere in the nucleation step and the particle growth step can be appropriately controlled, so that composite hydroxide particles having the above-described particle structure and a narrow particle size distribution can be easily produced. Obtainable. However, when the method for producing composite hydroxide particles of the present invention is applied, it is sufficient to appropriately install a sealing mechanism for strictly maintaining the sealing property in the reaction vessel. It is not necessary to strictly design the sealing mechanism to the extent that the complete sealing of the entire device including the connecting portions is ensured. For this reason, it is possible to reduce the cost required for the seal mechanism that accompanies the enlargement of the manufacturing apparatus.

2. Positive electrode active material for lithium ion secondary battery 2-1. Positive electrode active material for lithium ion secondary battery The positive electrode active material of the present invention has the general formula (B): Li _1+u Ni _x Co _y Mn _z M _t O ₂ (−0.05≦u≦0.50, x+y+z+t=1 , 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, M is Mg, Ca, Al, Ti, V, One or more additional elements selected from the group consisting of Cr, Zr, Nb, Mo, Hf, Ta and W) hexagonal lithium transition metal composite oxide particles (hereinafter referred to as "lithium transition metal composite oxide (referred to as "matter particles"). This positive electrode active material consists of secondary particles formed by aggregation of a plurality of primary particles, and has an average particle size MV in the range of 2.0 μm to 4.0 μm, which is an index showing the spread of the particle size distribution [ (d90−d10)/average particle diameter MV] is 0.50 or less, the tap density is 1.2 g/cm ³ to 2.0 g/cm ³ , and the (003) plane peak in X-ray diffraction The crystallite diameter determined by the Scherrer formula is 1000 Å to 1400 Å.

(1) Composition The value of u, which indicates the excess amount of lithium (Li), is −0.05 or more and 0.50 or less, preferably 0 or more and 0.50 or less, more preferably 0 or more and 0.35 or less. By limiting the value of u to the above range, the output characteristics and capacity characteristics of the secondary battery can be improved. On the other hand, when the value of u is less than −0.05, the positive electrode resistance of the secondary battery becomes large, and the output characteristics cannot be improved. On the other hand, when it exceeds 0.50, not only the initial discharge capacity decreases, but also the positive electrode resistance increases.

Nickel (Ni) is an element that contributes to increasing the potential and capacity of a secondary battery. .9 or less. If the value of x is less than 0.3, the capacity characteristics of the secondary battery cannot be improved. On the other hand, if the value of x exceeds 0.95, the content of other elements will decrease and the effect cannot be obtained.

Manganese (Mn) is an element that contributes to the improvement of thermal stability, and the value of y indicating its content is 0 or more and 0.4 or less, preferably 0.10 or more and 0.35 or less . When the value of y exceeds 0.4 , Mn is eluted from the positive electrode active material during high-temperature operation, resulting in deterioration of charge-discharge cycle characteristics.

Cobalt (Co) is an element that contributes to the improvement of charge-discharge cycle characteristics, and the value of z indicating its content is 0.05 or more and 0.55 or less, preferably 0.10 or more and 0.40 or less. . When the value of z exceeds 0.55 , the initial discharge capacity of the secondary battery is significantly reduced.

In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material of the present invention may contain an additive element M in addition to the metal elements described above. Such additive elements M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum At least one selected from the group consisting of (Mo), hafnium (Hf), tantalum (Ta) and tungsten (W) can be used.

The value of t, which indicates the content of the additive element M, is preferably 0 or more and 0.1 or less, more preferably 0.001 or more and 0.05 or less. If the value of t exceeds 0.1, the metal element that contributes to the Redox reaction decreases, resulting in a decrease in battery capacity of the secondary battery.

The additive element M may be dispersed uniformly inside the particles of the positive electrode active material, or may coat the particle surfaces of the positive electrode active material. Furthermore, the surface may be coated after being uniformly dispersed inside the particles. In any case, it is necessary to control the content of the additive element M to be within the above range.

Further, when further improving the capacity characteristics of the secondary battery in the positive electrode active material represented by the general formula (B), the composition is represented by the general formula (B1): Li _1+u Ni _x Co _y Mnz _{M t} O ₂ (However, -0.05 ≤ u ≤ 0.20, x + y + z + t = 1, 0.7 < x ≤ 0.95, 0.05 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.2, 0 ≤ t ≤ 0.1, M is one or more additive elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo and W). preferable. In particular, when achieving compatibility with thermal stability, the value of x in the general formula (B1) is more preferably 0.7 < x ≤ 0.9, and 0.7 < x ≤ 0.85. is more preferred.

On the other hand, in order to further improve the thermal stability of the secondary battery, the composition thereof is represented by the general formula (B2): Li _1+u Ni _x Co _y Mn _z M _t O ₂ (where −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 Al, Ti, V , Cr, Zr, Nb, Mo, Hf, Ta and W).

(2) Particle Structure The positive electrode active material of the present invention is composed of secondary particles formed by aggregation of a plurality of primary particles. In the present invention, the positive electrode active material may be composed of secondary particles having a highly dense particle structure, and the particle structure itself is not particularly limited.

Such secondary particles can be composed of solid secondary particles having a solid structure formed by aggregation of a plurality of primary particles. Alternatively, it can be composed of hollow secondary particles having a hollow structure having a hollow inside the particle. However, it is preferable that these solid secondary particles and hollow secondary particles are mixed.

When the solid secondary particles and the hollow secondary particles are mixed, the existence ratio of the solid secondary particles and the hollow secondary particles is preferably in the range of 1:9 to 9:1, It is more preferably in the range of 2:8 to 8:2, even more preferably in the range of 3:7 to 7:3. If the abundance ratio is out of the above range and the number of solid secondary particles is too large, the reaction area with the electrolyte becomes relatively small, the positive electrode resistance of the secondary battery increases, and the output characteristics deteriorate. trend. On the other hand, when the number of hollow secondary particles is too large, the tap density becomes small, the filling density of the positive electrode active material is lowered, and the battery capacity per unit volume of the secondary battery tends to be lowered.

In the hollow secondary particles, the average ratio of the outer diameter of the hollow portion to the particle diameter is preferably in the range of 10% to 50%, more preferably in the range of 20% to 40%, and 25% to More preferably it is in the range of 35%. If the average ratio of the outer diameter of the hollow portion to the particle size exceeds 50%, the hollow portion becomes too large, and the ratio of the positive electrode active material when filled as the positive electrode material becomes too small, and the secondary battery is insufficient. sufficient charge/discharge capacity cannot be ensured. In addition, the strength of the particles may be lowered, and the particles may be broken and fine powder may be generated when forming the positive electrode of the secondary battery. On the other hand, if the average ratio of the outer diameter of the hollow portion to the particle size is less than 10%, the effect of reducing the reaction resistance due to the contact between the inner wall of the hollow portion and the electrolytic solution is not sufficiently large, so the internal resistance of the secondary battery is reduced. I can't. However, in the present invention, it is sufficient to treat such secondary particles having an average ratio of the outer diameter of the hollow portion to the particle diameter of less than 10% as solid secondary particles.

In addition, the average ratio of the outer diameter of the hollow portion to the particle size of the hollow secondary particles is determined by a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM), as in the case of the composite hydroxide particles. It can be obtained by observing the cross section.

(3) Average particle size MV of secondary particles
The positive electrode active material of the present invention has an average particle diameter MV of 2.0 μm to 4.0 μm, preferably 2.4 μm to 3.6 μm, more preferably 2.5 μm to 3.5 μm. If the average particle diameter MV of the positive electrode active material is in such a range, not only can the battery capacity per unit volume of the secondary battery be increased, but also the safety and output characteristics of the secondary battery can be improved. can be done. On the other hand, if the average particle size MV is less than 2.0 μm, the filling property of the positive electrode active material is lowered, and the battery capacity per unit volume of the secondary battery cannot be increased. On the other hand, when the average particle diameter MV exceeds 4.0 μm, the specific surface area of the positive electrode active material is reduced, and when a secondary battery is formed, the reaction area with the electrolyte solution is reduced, so the output of the secondary battery is reduced. Characteristics cannot be improved.

The average particle diameter MV of the positive electrode active material means the volume-based average particle diameter, as in the case of the composite hydroxide particles described above. can ask.

(4) Particle size distribution The positive electrode active material of the present invention is composed of small-sized lithium composite oxide particles having an average particle size MV in the range of 2.0 μm to 4.0 μm, but the lithium composite oxide particles [(d90-d10)/average particle size MV], which is an index showing the spread of the particle size distribution of , is 0.50 or less, preferably 0.47 or less, more preferably 0.45 or less, and a sharp particle size distribution have achieved Such a positive electrode active material has a low proportion of fine particles and coarse particles, and a secondary battery using the same maintains an excellent level of safety and cycle characteristics while increasing output characteristics. be able to.

On the other hand, when [(d90-d10)/average particle diameter MV] exceeds 0.50, the proportion of fine particles and coarse particles increases. For example, a secondary battery using a positive electrode active material with a large proportion of fine particles generates heat due to local reactions of fine particles, lowers safety, and selectively deteriorates fine particles. , the cycle characteristics are inferior. Such a problem becomes conspicuous as the output of the positive electrode active material is increased. In addition, a secondary battery using a positive electrode active material with a large proportion of coarse particles cannot secure a sufficient reaction area between the electrolyte and the positive electrode active material, resulting in inferior output characteristics.

On the other hand, assuming industrial-scale production, it is not realistic to use a positive electrode active material with an excessively small [(d90-d10)/average particle size MV]. Therefore, considering cost and productivity, the lower limit of [(d90-d10)/average particle size MV] is preferably about 0.25.

Note that the meanings of d10 and d90 in the index [(d90-d10)/average particle diameter MV] indicating the spread of the particle size distribution, and the method for obtaining these are the same as for the composite hydroxide particles described above, so here description is omitted.

(5) Tap Density The positive electrode active material of the present invention has a tap density of 1.2 g/cm ³ to 2.0 g/cm 3 , which is an index of the denseness of the lithium composite oxide particles constituting the positive electrode active material and the filling property of the particles. 0 g/cm ³ , preferably 1.3 g/cm ³ to 1.9 g/cm ³ , more preferably 1.4 g/cm ³ to 1.8 g/cm ³ . If the tap density of the positive electrode active material is within this range, the positive electrode active material can be made of small-sized lithium composite oxide particles with an average particle size MV in the range of 2.0 μm to 4.0 μm. Since it has a high energy density, not only can the battery capacity per unit volume of the secondary battery be increased, but also the cycle characteristics can be improved at the same time.

On the other hand, if the tap density is less than 1.2 g/cm ³ , the fillability of the positive electrode active material is low, and the overall capacity characteristics of the secondary battery may not be sufficiently improved. On the other hand, when the tap density exceeds 2.0 g/cm ³ , the specific surface area of the positive electrode active material is reduced, so that when a secondary battery is formed, the reaction area with the electrolyte solution is reduced. Output characteristics cannot be improved.

(6) Crystallite size In the positive electrode active material of the present invention, when the crystallite size of the primary particles is obtained using the Scherrer formula from the half-value width of the peak of the (003) plane by X-ray diffraction, the crystallite size is is in the range of 1000 Å to 1400 Å, preferably 1100 Å to 1300 Å, more preferably 1150 Å to 1250 Å. A positive electrode active material having a crystallite diameter within such a range has extremely high crystallinity, and can reduce the positive electrode resistance of a secondary battery and improve its output characteristics.

On the other hand, when the crystallite diameter of the (003) plane is less than 1000 Å, the primary particles are fine, and the pores existing between the primary particles in the positive electrode active material become too fine, resulting in Since it becomes difficult for the electrolyte to penetrate into the secondary battery, the reaction area with the electrolyte decreases, and the output characteristics of the secondary battery deteriorate. On the other hand, if the crystallite diameter of the (003) plane exceeds 1400 Å, the primary particles become too coarse, the ratio of pores in the secondary particles is extremely reduced, and the penetration path of the electrolyte is reduced. , the reaction area with the electrolyte decreases, and the output characteristics of the secondary battery deteriorate. In the stage of the positive electrode active material, it is sufficient to evaluate the particle properties of the primary particles constituting the lithium composite oxide particles based on the above crystallite size, but the average particle size MV of the primary particles is 0.1 μm. It is preferably in the range of ~0.5 μm.

2-2. Method for producing positive electrode active material for lithium ion secondary battery The method for producing the positive electrode active material of the present invention uses the composite hydroxide particles of the present invention as a precursor, is represented by the general formula (B), and has a hexagonal system. As long as it is possible to synthesize a positive electrode active material composed of lithium composite oxide particles and having the aforementioned particle structure, average particle size MV, particle size distribution, tap density and crystallite size, there is no particular limitation. However, by adopting the following method, such a positive electrode active material can be efficiently synthesized. That is, the method for producing a positive electrode active material of the present invention comprises a mixing step of mixing the composite hydroxide particles of the present invention and a lithium compound to obtain a lithium mixture, and and a firing step of firing with. In addition, if necessary, steps such as a heat treatment step, a calcining step, and a crushing step may be added to these steps. Hereinafter, the manufacturing method of the positive electrode active material of the present invention will be described step by step.

(1) Heat treatment step In the method for producing a positive electrode active material of the present invention, optionally, a heat treatment step may be provided before the mixing step, and the composite hydroxide particles may be mixed with the lithium compound after being treated as heat treated particles. . Here, the heat-treated particles include not only composite hydroxide particles from which excess moisture has been removed in the heat treatment step, but also transition metal composite oxide particles converted to oxides in the heat treatment step (hereinafter referred to as "composite oxide particles ), or mixtures thereof.

The heat treatment step is a step of removing excess moisture contained in the composite hydroxide particles by heating the composite hydroxide particles to a predetermined temperature for heat treatment. As a result, it is possible to reduce the amount of water remaining until after the baking process to a certain amount, so that variations in the composition of the obtained positive electrode active material can be suppressed.

The heating temperature in the heat treatment step is preferably 105°C to 750°C, more preferably 500°C to 700°C. If the heating temperature is less than 105° C., excess moisture in the composite hydroxide particles cannot be removed, and variations may not be sufficiently suppressed. On the other hand, if the heating temperature exceeds 750° C., the particles are sintered by the heat treatment, resulting in deterioration of the particle size distribution.

In the heat treatment step, it is sufficient to remove moisture to the extent that the number of atoms of each metal component in the positive electrode active material and the ratio of the number of Li atoms do not vary. There is no need to convert to oxide particles. However, in order to reduce the variation in the number of atoms of each metal component and the ratio of the number of Li atoms, all the composite hydroxide particles are converted into composite oxide particles by heating to 500 ° C. or higher. Conversion is preferred. In addition, depending on the heat treatment conditions, the metal components contained in the heat-treated particles are determined in advance by analysis, and based on this, the mixing ratio with the lithium compound is determined, so that the above-mentioned variations can be further suppressed. .

The atmosphere in which the heat treatment is performed is not particularly limited as long as it is a non-reducing atmosphere.

In addition, the heat treatment time is not particularly limited, but from the viewpoint of sufficiently removing excess moisture in the composite hydroxide particles, it is preferably at least 1 hour or more, and more preferably 5 hours to 15 hours.

Such a heat treatment step may be any one capable of heat-treating the composite hydroxide particles under the above conditions, and an electric furnace that does not generate gas can be suitably used.

(2) Mixing Step The mixing step is a step of mixing the above composite hydroxide particles or heat-treated particles with a lithium-containing substance such as a lithium compound to obtain a lithium mixture.

In the mixing step, the ratio (Li /Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, still more preferably 1.0 to 1.2. It is necessary to mix hydroxide particles or heat-treated particles with the lithium compound. That is, since Li/Me does not change before and after the firing process, the composite hydroxide particles or heat-treated particles and lithium It is necessary to mix the compounds.

Although the lithium compound used in the mixing step is not particularly limited, it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof in terms of availability. In particular, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate.

It is preferable that the composite hydroxide particles or the heat-treated particles and the lithium compound are sufficiently mixed to the extent that fine powder is not generated. Insufficient mixing may cause variations in Li/Me among individual particles, making it impossible to obtain sufficient battery characteristics. In addition, a general mixer can be used for mixing. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

(3) Calcination step When lithium hydroxide or lithium carbonate is used as the lithium compound, after the mixing step and before the firing step, the lithium mixture is heated to a temperature lower than the firing temperature described later and at a temperature of 350 ° C. or higher. A calcination step of calcining at a temperature in the range of 800° C., preferably 450° C. to 780° C., that is, at the reaction temperature of lithium hydroxide or lithium carbonate and composite hydroxide particles or heat-treated particles may be performed. . As a result, lithium can be sufficiently diffused in the composite hydroxide particles or heat-treated particles, and more uniform lithium composite oxide particles can be obtained.

The holding time at the above temperature is preferably 1 hour to 10 hours, more preferably 3 hours to 6 hours. The atmosphere in the calcining step is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume to 100% by volume, as in the firing step described later.

(4) Firing step In the firing step, the lithium mixture obtained in the mixing step is fired under predetermined conditions, lithium is diffused into the composite hydroxide particles or heat-treated particles, and lithium composite oxide particles (positive electrode active material ) is obtained.

In the firing step, among the composite oxide particles or the heat-treated particles, the fine primary particles that make up the center of the two-layer particles are more dense than the plate-like primary particles that make up the outer shell and solid particles of the two-layer particles. Start sintering from a low temperature. Moreover, the amount of shrinkage is greater than that of the outer shell portion or solid particles composed of plate-like primary particles. Therefore, of the two-layer particles, the fine primary particles that make up the central portion shrink toward the outer shell portion, where sintering progresses slowly. become hollow secondary particles. On the other hand, solid particles become solid secondary particles having a solid structure by firing.

The furnace used in the firing step is not particularly limited as long as it can heat the lithium mixture in the atmosphere or in an oxygen stream. However, from the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace can be suitably used. This also applies to furnaces used in the heat treatment process and the calcining process.

[Firing temperature]
The firing temperature of the lithium mixture is required to be 650°C to 980°C. If the firing temperature is less than 650 ° C., lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, and excess lithium or unreacted composite hydroxide particles or heat-treated particles remain, or the obtained lithium composite In some cases, the crystallinity of the oxide particles becomes insufficient. On the other hand, if the sintering temperature exceeds 980° C., intense sintering occurs between the lithium composite oxide particles, causing abnormal grain growth and increasing the proportion of amorphous coarse particles.

It should be noted that the firing temperature is preferably 650° C. to 900° C. in order to obtain the positive electrode active material represented by the general formula (B1) described above. On the other hand, when the positive electrode active material represented by the general formula (B2) is to be obtained, the firing temperature is preferably 800°C to 980°C.

In addition, the heating rate in the firing step is preferably 2° C./min to 10° C./min, more preferably 5° C./min to 10° C./min. Furthermore, during the firing step, it is preferable to hold the temperature near the melting point of the lithium compound for preferably 1 to 5 hours, more preferably 2 to 5 hours. Thereby, the composite hydroxide particles or the heat-treated particles and the lithium compound can be reacted more uniformly.

[Baking time]
Of the firing time, the retention time at the firing temperature described above is preferably at least 2 hours or longer, more preferably 4 to 24 hours. When the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, and excess lithium or unreacted composite hydroxide particles or heat-treated particles remain or are not obtained. The crystallinity of the lithium composite oxide particles obtained may become insufficient.

The cooling rate from the firing temperature to at least 200° C. after the holding time is preferably 2° C./min to 10° C./min, more preferably 33° C./min to 77° C./min. By controlling the cooling rate within such a range, it is possible to prevent damage to equipment such as a sagger due to rapid cooling while ensuring productivity.

[Firing atmosphere]
The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume to 100% by volume, and a mixed atmosphere of oxygen and an inert gas having the above oxygen concentration. Especially preferred. That is, it is preferable to carry out the calcination in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium composite oxide particles may be insufficient.

(5) Crushing step The lithium composite oxide particles obtained by the firing step may be aggregated or slightly sintered. In such a case, it is preferable to pulverize the aggregates or sintered bodies of the lithium composite oxide particles. Thereby, the average particle size MV and particle size distribution of the positive electrode active material to be obtained can be adjusted to a suitable range. Crushing means applying mechanical energy to agglomerates consisting of a plurality of secondary particles generated by sintering necking between secondary particles during firing, without almost destroying the secondary particles themselves. It means the operation of separating and loosening aggregates.

As a crushing method, known means can be used, for example, a pin mill or a hammer mill can be used. At this time, it is preferable to adjust the crushing force within an appropriate range so as not to destroy the secondary particles.

3. Lithium-Ion Secondary Battery The lithium-ion secondary battery of the present invention includes components such as a positive electrode, a negative electrode, and an electrolyte, which are the same as those of ordinary lithium-ion secondary batteries. In the following, a lithium ion secondary battery using a non-aqueous electrolytic solution obtained by dissolving a lithium salt, which is a supporting salt, in an organic solvent as an electrolyte will be described, but the lithium ion secondary battery of the present invention It is also possible to apply various modifications and improvements based on the embodiments described herein. In addition, a solid electrolyte secondary battery using a nonflammable and ionically conductive solid electrolyte such as Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ or Li ₂ S—SiS ₂ as the electrolyte. It is also applicable to lithium ion secondary batteries containing

(1) Components a) Positive Electrode Using the positive electrode active material for a lithium ion secondary battery obtained by the present invention, a positive electrode for a lithium ion secondary battery is produced, for example, as follows.

First, a powdered positive electrode active material is mixed with a conductive material and a binder, and if necessary, activated carbon and a solvent for adjusting viscosity are added, and the mixture is kneaded to prepare a positive electrode mixture paste. At that time, the mixing ratio of each component in the positive electrode mixture paste is also an important factor that determines the performance of the lithium ion secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass, similar to the positive electrode of a general lithium ion secondary battery, and the conductive material can be 1 part by mass to 20 parts by mass, and the content of the binder can be 1 part by mass to 20 parts by mass.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size depending on the intended battery, and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the above examples, and other methods may be used.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and Polyacrylic acid can be used.

Further, if necessary, a solvent for dispersing the positive electrode active material, the conductive material and the activated carbon and dissolving the binder can be added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. Activated carbon can also be added to the positive electrode mixture in order to increase the electric double layer capacity.

b) Negative electrode For the negative electrode, a negative electrode mixture is prepared by mixing a binder with a negative electrode active material such as metallic lithium or a lithium alloy, or a negative electrode active material capable of intercalating and deintercalating lithium ions, and adding an appropriate solvent to form a paste. , copper or other metal foil, which is coated on the surface of a current collector, dried, and compressed to increase the electrode density as required.

Examples of negative electrode active materials include materials containing lithium such as metal lithium and lithium alloys, natural graphite capable of intercalating and deintercalating lithium ions, artificial graphite, sintered organic compounds such as phenolic resins, and carbon materials such as coke. A powder can be used. In this case, as the negative electrode binder, similarly to the positive electrode, a fluorine-containing resin such as PVDF can be used. of organic solvents can be used.

c) Separator The separator is sandwiched between the positive electrode and the negative electrode, and has the function of separating the positive electrode and the negative electrode and retaining the electrolyte. As such a separator, for example, a thin film of polyethylene, polypropylene, or the like and having many fine pores can be used, but there is no particular limitation as long as it has the above function.

d) Non-aqueous Electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

Organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; and ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. can.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used.

Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(2) Lithium-Ion Secondary Battery A lithium-ion secondary battery composed of the positive electrode, negative electrode, separator, and non-aqueous electrolyte described above can have various shapes such as a cylindrical shape and a laminated shape.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and communicated with the positive electrode collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and sealed in a battery case to complete the lithium ion secondary battery.

(3) Characteristics of lithium ion secondary battery Since the lithium ion secondary battery of the present invention uses the positive electrode active material of the present invention as a positive electrode material as described above, it has excellent capacity characteristics, output characteristics and cycle characteristics. . Moreover, it can be said that the secondary battery is superior in thermal stability and safety even in comparison with a secondary battery using a positive electrode active material composed of conventional lithium-nickel-based oxide particles. Specifically, in the positive electrode active material of the present invention, although the average particle size MV is in the range of 2 μm to 4 μm, which is an extremely small particle size, it has a sharp particle size distribution and a high tap density (particle compactness and packing property). , and high crystallinity are realized, compared to the conventional lithium ion secondary battery, the high capacity characteristics of the initial discharge capacity of 160 mAh / g or more, the capacity after 500 cycles of 81% or more High cycle characteristics such as retention rate and excellent output characteristics such as positive electrode resistance of 6Ω or less are realized.

(4) Applications The lithium-ion secondary battery of the present invention, as described above, is excellent in capacity characteristics, output characteristics and cycle characteristics. (computers, mobile phone terminals, etc.). In addition, the lithium-ion secondary battery of the present invention is excellent in safety, and not only can it be made smaller and higher in output, but it can also simplify the expensive protection circuit, so the mounting space is limited. It can also be suitably used as a power source for transportation equipment that receives power.

The present invention will be described in detail below using examples and comparative examples. In the following examples and comparative examples, reagent special grade samples manufactured by Wako Pure Chemical Industries, Ltd. were used to prepare the composite hydroxide particles and the positive electrode active material, unless otherwise specified. In addition, throughout the nucleation step and the particle growth step, the pH of the reaction aqueous solution is measured by a pH controller (Nisshin Rika NPH-690D), and the supply amount of the sodium hydroxide aqueous solution is adjusted based on the measured value. , the fluctuation width of the pH of the reaction aqueous solution in each step was controlled within a range of ±0.2.

(Example 1)
(a) Production of composite hydroxide particles [Nucleation step]
First, 14 L of water was put into a 60 L reactor, and the temperature inside the reactor was set to 40° C. while stirring at 750 rpm. At this time, nitrogen gas was introduced into the reaction vessel at a flow rate of 20 L/min and allowed to flow for 30 minutes to create a non-oxidizing atmosphere with an oxygen concentration of 0.6% by volume. Subsequently, appropriate amounts of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water were supplied into the reaction tank so that the pH value was 12.5 at a liquid temperature of 25° C. and the ammonium ion concentration was 10 g/L. to form a pre-reaction aqueous solution.

At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were added so that the molar ratio of the respective metal elements was Ni:Mn:Co:Zr=33.1:33.1:33.1:0.2. It was dissolved in water to prepare a 2 mol/L starting metal salt aqueous solution.

Next, this raw material aqueous reaction solution was supplied to the pre-reaction aqueous solution at 100 ml/min to form an aqueous solution for the nucleation step, and nucleation was performed for 1 minute. At this time, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times to maintain the pH and ammonium ion concentration of the aqueous solution for nucleation within the ranges described above.

[Particle growth step]
After the nucleation is completed, the supply of all the aqueous solution is temporarily stopped, and sulfuric acid is added to adjust the pH to 11.2 based on the liquid temperature of 25° C., thereby forming an aqueous solution for particle growth. did. After confirming that the pH value reached a predetermined value, the starting metal salt aqueous solution and the sodium tungstate aqueous solution were supplied to grow the nuclei (particles) generated in the nucleation step.

In the particle growth process, similarly to the nucleation process, nitrogen gas was introduced into the reaction vessel at a flow rate of 20 L / min, and the stock solution aqueous solution was supplied while maintaining the non-oxidizing atmosphere. The grain growth process was terminated by stopping the supply of . The oxygen concentration in the reaction atmosphere was 0.5% by volume. Thereafter, the obtained product was washed with water, filtered and dried to obtain powdery composite hydroxide particles.

In the grain growth step, a 25% by mass sodium hydroxide aqueous solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times throughout the process to maintain the pH and ammonium ion concentration of the aqueous solution for particle growth within the ranges described above.

(b) Evaluation of composite hydroxide particles [Composition]
According to analysis using an ICP emission spectrometer, this positive electrode active material is represented by the general formula: Li _1.14 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 (OH) ₂ It was confirmed that

[Average particle size MV, particle size distribution and tap density]
Using a laser light diffraction scattering particle size analyzer (manufactured by Nikkiso Co., Ltd., Microtrac HRA), the average particle size MV of the composite hydroxide particles was measured, and d10 and d90 were measured. The value of [(d90-d10)/average particle diameter MV], which is an index showing the spread of the particle size distribution, was 0.42. Also, the tap density was measured with a tapping machine (KRS-406, Kuramochi Scientific Instruments Manufacturing Co., Ltd.). As a result, it was confirmed to be 1.34 g/cm ³ .

[Abundance ratio of solid particles and double-layered particles]
A sample of the obtained composite oxide particles was embedded in a resin and subjected to cross-section polisher processing (CP processing). Observation (magnification: 5000 times) was performed. From the SEM image, the numbers of solid particles and double-layered particles were measured, and the existing ratio was calculated to be 7:3.

(c) Production of positive electrode active material The composite hydroxide particles obtained as described above were heat-treated at 120°C for 12 hours in an air stream (oxygen concentration: 21% by volume), and then the Li/Me ratio was 1.0%. 14 was sufficiently mixed with lithium carbonate using a shaker mixer (TURBULA Type T2C manufactured by Willie & Bachoffen (WAB)) to obtain a lithium mixture (mixing step).

This lithium mixture is heated to 950° C. at a temperature elevation rate of 2.5° C./min in an air stream (oxygen concentration: 21% by volume), and is calcined by holding at this temperature for 4 hours. Cooled to room temperature at about 4°C/min. Aggregation or mild sintering occurred in the positive electrode active material thus obtained. Therefore, the positive electrode active material was pulverized to adjust the average particle size MV and the particle size distribution.

(d) Evaluation of positive electrode active material [Composition]
According to analysis using an ICP emission spectrometer, this positive electrode active material is represented by the general formula: Li _1.14 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ It was confirmed that it is.

[Average particle size MV, particle size distribution, and tap density]
The average particle size MV, d10 and d90 of the composite hydroxide particles were measured using a laser diffraction scattering particle size analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.). The average particle size MV was 3.10 μm, and the index [(d90−d10)/average particle size MV], which is an index showing the spread of the particle size distribution, was 0.44. Also, the tap density was measured with a tapping machine (KRS-406, Kuramochi Scientific Instruments Manufacturing Co., Ltd.). As a result, it was confirmed that the tap density was 1.47 g/cm ³ .

[Crystallite diameter]
Using an X-ray diffractometer (manufactured by PANalytical, X'Pert PRO), analysis is performed by powder X-ray diffraction using CuKα rays, and the diffraction peaks of the line diffraction pattern are excluded from the broadening of the diffraction peaks. was used to calculate the crystallite size of the (003) plane, which was 1191 Å.

[Proportion of solid secondary particles and hollow secondary particles]
The obtained composite oxide particles were similarly observed by SEM (magnification: 5000 times). The results are shown in FIG. Also, the number of solid secondary particles and hollow secondary particles was measured from the SEM image, and the abundance ratio was calculated to be 7:3.

(e) Preparation of secondary battery: 52.5 mg of the positive electrode active material obtained as described above, 15 mg of acetylene black, and 7.5 mg of PTEE were mixed, and the pressure was 100 MPa, and the diameter was 11 mm and the thickness was 11 mm. After press molding to 100 μm, it was dried at 120° C. for 12 hours in a vacuum dryer to prepare a positive electrode (1).

Next, using this positive electrode (1), a 2032-type coin battery (B) having the structure schematically shown in FIG. Lithium metal with a diameter of 17 mm and a thickness of 1 mm was used for the negative electrode (2) of this 2032 type coin battery, and the electrolyte was ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as the supporting electrolyte. (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used for the separator (3). The 2032-type coin battery (B) has a gasket (4) and is assembled into a coin-shaped battery with a positive electrode can (5) and a negative electrode can (6).

(f) Battery evaluation [initial discharge capacity]
A 2032-type coin battery was left for about 24 hours after it was produced, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA/cm ² and the cutoff voltage was set to 4.3 V. A charge/discharge test was performed to measure the discharge capacity when the battery was discharged to a cut-off voltage of 3.0 V after a 1-hour rest, and the initial discharge capacity was determined. As a result, it was confirmed that the initial discharge capacity was 160.2 mAh/g. A multi-channel voltage/current generator (R6741A, manufactured by Advantest Co., Ltd.) was used to measure the charge/discharge capacity.

[Positive resistance]
Using a 2032-type coin battery charged at a charging potential of 4.1 V, the resistance value was measured by the AC impedance method. For the measurement, a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron) were used to obtain a Nyquist plot. Since the plot appears as the sum of characteristic curves representing solution resistance, negative electrode resistance and capacity, and positive electrode resistance and capacity, fitting calculation was performed using an equivalent circuit to calculate the value of positive electrode resistance. As a result, it was confirmed that the positive electrode resistance was 5.31Ω.

[Cycle characteristics]
The charge/discharge test described above was repeated, and the 500th cycle capacity retention rate was calculated by measuring the 500th discharge capacity relative to the initial discharge capacity. As a result, it was confirmed that the 500-cycle capacity retention rate was 82.2%.

(Example 2)
In the nucleation step and the particle growth step, the composite hydroxide particles, the positive electrode active material and the two The following battery was obtained and evaluated. The results are shown in Tables 2 and 3.

(Example 3)
In the nucleation step and the particle growth step, the composite hydroxide particles, the positive electrode active material and the two The following battery was obtained and evaluated. The results are shown in Tables 2 and 3.

(Example 4)
In the nucleation step and the particle growth step, the composite hydroxide particles, the positive electrode active material and the two The following battery was obtained and evaluated. The results are shown in Tables 2 and 3.

(Comparative example 1)
In the nucleation step and the particle growth step, the composite hydroxide particles, the positive electrode active material and the two The following battery was obtained and evaluated. The results are shown in Tables 2 and 3 and FIG.

(Comparative example 2)
In the nucleation step and the particle growth step, the composite hydroxide particles, the positive electrode active material and the two The following battery was obtained and evaluated. The results are shown in Tables 2 and 3.

(Comparative Example 3)
In the nucleation step, air was introduced into the reaction tank at a flow rate of 2 L/min, the reaction atmosphere was an oxidizing atmosphere, the oxygen concentration was 21% by volume, and the time of the nucleation step was 30 minutes. , and the flow rate of the nitrogen gas introduced into the reaction vessel in the particle growth step was changed to 10 L/min in the same manner as in Example 1 to produce the composite hydroxide particles, the positive electrode active material and the secondary A battery was obtained and evaluated. The results are shown in Tables 2, 3 and FIG.

Claims (5)

A raw material aqueous solution containing at least a transition metal and an aqueous solution containing ammonium ions are supplied into a reaction vessel to form a reaction aqueous solution, and a precursor of a positive electrode active material for a lithium ion secondary battery is formed by a crystallization reaction. A method for producing transition metal composite hydroxide particles comprising
A nucleation step of adjusting the pH value of the reaction aqueous solution in the range of 12.0 to 14.0 at a liquid temperature of 25 ° C. to generate nuclei;
The pH value of the reaction aqueous solution containing the nuclei obtained in the nucleation step at a liquid temperature of 25 ° C. is lower than the pH value in the nucleation step and is in the range of 10.5 to 12.0. a particle growth step of growing the nucleus under control of
Through the nucleation step and the particle growth step, an inert gas is continuously blown into the reaction vessel at a flow rate of 0.2 L / min to 0.7 L / min per 1 L of the internal volume of the reaction vessel, and the nucleation step and the reaction atmosphere in the particle growth step is a non-oxidizing atmosphere with an oxygen concentration of 0.3 % by volume or more and 0.6% by volume or less,
A method for producing transition metal composite hydroxide particles. General formula (A): _NixCoyMnzMt (OH) _2+a (where _x + y + _z + _t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0 .4, 0≤t≤0.1 and 0≤a≤0.5, and M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W one or more additive elements selected from the group), transition metal composite hydroxide particles consisting of secondary particles formed by agglomeration of a plurality of primary particles,
The secondary particles have an average particle size MV in the range of 2.0 μm to 4.0 μm, and the index [(d90−d10)/average particle size MV], which is an index showing the spread of the particle size distribution, is 0.50 or less. with a tap density in the range of 1.2 g/cm ³ to 2.0 g/cm ³ ,
The secondary particles include solid particles formed by aggregation of plate-shaped primary particles, a central portion formed by aggregation of fine primary particles smaller than the plate-shaped primary particles, and an outer side of the central portion. and a two-layer particle composed of an outer shell portion formed by aggregating the plate-like primary particles,
The existence ratio of the solid particles and the bilayer particles is in the range of 2:8 to 8:2.
Transition metal composite hydroxide particles. A mixing step of mixing the transition metal composite hydroxide particles according to claim 2 and a lithium compound to form a lithium mixture;
a firing step of firing the lithium mixture at a temperature in the range of 650° C. to 980° C. in an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume;
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: General formula (B): Li _1+u Ni _x Co _y Mn _z M _t O ₂ (where −0.05≦u≦0.50, x+y+z+t=1, 0.3≦x≦0.95, 0.05≦ y≦0.55, 0≦z≦0.4, 0≦t≦0.1, M is the group of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W One or more additive elements selected from), a positive electrode active material for a lithium ion secondary battery composed of hexagonal lithium-transition metal composite oxide particles,
Consisting of secondary particles formed by aggregation of primary particles,
The secondary particles have an average particle size MV in the range of 2.0 μm to 4.0 μm, and the index [(d90−d10)/average particle size MV], which is an index showing the spread of the particle size distribution, is 0.50 or less. The tap density is in the range of 1.2 g/cm ³ to 2.0 g/cm ³ , and the crystallite diameter determined by the Scherrer formula from the (003) plane peak in X-ray diffraction is in the range of 1000 Å to 1400 Å. located in
The secondary particles are composed of solid secondary particles formed by agglomeration of a plurality of primary particles and hollow secondary particles having a hollow structure inside the particles,
The existence ratio of the solid secondary particles and the hollow secondary particles is in the range of 2:8 to 8:2,
Positive electrode active material for lithium ion secondary batteries. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode active material for a lithium ion secondary battery according to claim 4 is used as a positive electrode material for the positive electrode.

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