JP7183814B2 - Nickel-manganese-cobalt-containing composite hydroxide 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 relates to a nickel-manganese-cobalt-containing composite hydroxide that is a precursor of a positive electrode active material for a lithium-ion secondary battery, a method for producing the same, and lithium-nickel-manganese-cobalt obtained by using the nickel-manganese-cobalt-containing composite hydroxide as a precursor. The present invention relates to a positive electrode active material for lithium ion secondary batteries comprising a composite oxide, a method for producing the same, and a lithium ion secondary battery using the positive electrode active material for lithium ion secondary batteries as a positive electrode material.

In recent years, with the spread of mobile electronic devices such as smart phones, tablet terminals, digital cameras, 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. The lithium-ion secondary battery consists of a negative electrode, a positive electrode, a non-aqueous electrolyte or a solid electrolyte, etc. The active material used for the negative electrode and positive electrode is a material capable of desorbing and intercalating lithium. used. As the non-aqueous electrolyte , there is a non-aqueous electrolytic solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent. be.

Among these lithium ion secondary batteries, a lithium ion secondary battery using a lithium transition metal-containing composite oxide having a layered rock salt or spinel structure as a positive electrode material can obtain a voltage of 4V class, so it has high energy. Research and development and practical application are proceeding as a battery having a high density.

As a positive electrode material for such a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, lithium nickel manganese cobalt composite oxide (LiNi _1/3 Mn _1/3 Co _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 other lithium-transition metal-containing composite oxides have been proposed.

In recent years, among _these lithium-transition metal _- containing composite oxides, _at least nickel, _manganese , and A ternary positive electrode active material composed of a cobalt-containing lithium-nickel-manganese-cobalt-containing composite oxide (NMC) has excellent thermal stability, high capacity, good battery capacity cycle characteristics, and low resistance. It is attracting attention as a material that can obtain high output in Lithium-nickel-manganese-cobalt composite oxide is a compound having a layered crystal structure, like lithium-cobalt composite oxide and lithium-nickel composite oxide.

Regarding lithium-transition metal-containing composite oxides, emphasis is placed on the development of higher output by reducing internal resistance, and lithium-nickel-cobalt-aluminum-containing composite oxides ( NCA) is also drawing attention, but the lithium-nickel-manganese-cobalt-containing composite oxide is superior in weather resistance and easier to handle than the lithium-nickel-cobalt-aluminum-containing composite oxide. It is considered the most important in the development of lithium transition metal-containing composite oxides.

A ternary positive electrode active material composed of a lithium-nickel-manganese-cobalt-containing composite oxide is highly demanded to have a higher output due to a further reduction in internal resistance, particularly in power supply applications for electric vehicles.

In order to improve the output characteristics and cycle characteristics of the lithium-nickel-manganese-cobalt-containing composite oxide, first, the lithium-nickel-manganese-cobalt-containing composite oxide is composed of particles having a small particle size of about 3 μm to 10 μm and a narrow particle size distribution. It is necessary that By using particles with a small particle size, the specific surface area is large, and when used as a positive electrode active material, a sufficient reaction area with the electrolyte can be secured. - Since the moving distance between the negative electrodes can be shortened, it is possible to reduce the positive electrode resistance. In addition, by using particles with a narrow particle size distribution, the voltage applied to the particles in the electrode can be made uniform, so it is possible to suppress a decrease in battery capacity due to selective deterioration of the fine particles.

In addition, in order to further improve the output characteristics, research and development are also proceeding on improving the particle structure of lithium-nickel-manganese-cobalt-containing composite oxides. For example, in order to improve the output characteristics, it is considered effective to form a space into which the electrolyte can enter inside the positive electrode active material. By adopting such a structure, the positive electrode resistance can be significantly reduced because the reaction area with the electrolyte can be increased compared to a positive electrode active material with a solid structure having approximately the same particle size. It becomes possible. It is known that the positive electrode active material inherits the particle properties of the transition metal-containing composite hydroxide as its precursor. That is, in order to obtain the positive electrode active material described above, it is necessary to appropriately control the particle size, particle size distribution, particle structure, etc. of the secondary particles of the transition metal-containing composite hydroxide, which is the precursor thereof. .

For example, in WO2014/181891 and JP-A-2018-104275, an aqueous solution for nucleation containing at least a metal compound containing a transition metal and an ammonium ion donor has a pH value of 12.0 to 14.0. The pH value of the nucleation step for generating nuclei and the aqueous solution for particle growth containing the generated nuclei is lower than the pH value of the nucleation step and is 10.5 to 12.0. A non-oxidizing atmosphere is provided at the beginning of the nucleation step and the grain growth step, and at a predetermined timing in the grain growth step, the atmosphere is switched to an oxidizing atmosphere, Again, a method for producing a transition metal-containing composite hydroxide is disclosed, characterized in that the atmosphere is controlled twice to switch to a non-oxidizing atmosphere. According to this method, it has a small particle size and a narrow particle size distribution, and has a central portion formed by agglomeration of plate-like or needle-like primary particles, and is formed by agglomeration of fine primary particles outside the central portion. It is possible to obtain a transition metal-containing composite hydroxide composed of secondary particles having two laminated structures in which low-density layers formed by agglomeration of plate-like primary particles are alternately laminated. A positive electrode active material whose precursor is a transition metal-containing composite hydroxide having such a structure has a small particle size, a narrow particle size distribution, and a porous structure having spaces. In a secondary battery using such a positive electrode active material having a porous structure, it is possible to improve capacity characteristics, cycle characteristics, and output characteristics.

WO2014/181891 JP 2018-104275 A

However, according to the study of the present inventors, in order to further increase the energy density in the positive electrode active material composed of a lithium-nickel-manganese-cobalt-containing composite oxide composed of secondary particles having a porous structure, the nickel ratio can be increased. When compared with a lithium-nickel-manganese-cobalt-containing composite oxide in which the ratio of nickel, manganese, and cobalt is 1:1:1, contact with the electrolyte accelerates the deterioration of the grain structure, resulting in It has been found that the durability of the positive electrode active material is impaired, resulting in an increase in internal resistance (interfacial resistance of the positive electrode) and a decrease in output characteristics.

In view of such problems, the present invention improves the durability of a positive electrode active material made of a lithium-nickel-manganese-cobalt-containing composite oxide with an increased nickel ratio, and the effect of improving the output characteristics is sufficiently improved. realizing a guaranteed grain structure and a grain structure of a nickel-manganese-cobalt-containing composite hydroxide as a precursor for realizing such a positive electrode active material structure, and such An object of the present invention is to provide means for industrially efficiently producing a positive electrode active material having a similar structure and a precursor thereof.

The present invention provides a positive electrode active material precursor for a ternary lithium ion secondary battery comprising a lithium-nickel-manganese-cobalt-containing composite oxide (NMC) containing at least nickel, manganese, and cobalt as transition metals. A nickel-manganese-cobalt-containing composite hydroxide and its production method, a ternary positive electrode active material obtained by using the nickel-manganese-cobalt-containing composite hydroxide as a precursor, a production method thereof, and a positive electrode using the positive electrode active material It relates to a lithium ion secondary battery used as a material.

The nickel-manganese-cobalt-containing composite hydroxide according to the first aspect of the present invention is a precursor of a positive electrode active material for a lithium ion secondary battery, comprising a plurality of plate-like primary particles and particles smaller than the plate-like primary particles. It consists of secondary particles formed by aggregation of fine primary particles.

The secondary particles constituting the nickel-manganese-cobalt-containing composite hydroxide of the present invention include a central portion formed mainly by agglomeration of the plate-like primary particles, and mainly the fine primary particles outside the central portion. A first low-density layer formed by aggregation, a high-density layer formed mainly by aggregation of the plate-shaped primary particles outside the first low-density layer, and outside the high-density layer, a second low-density layer formed mainly by agglomeration of the fine primary particles; an outer shell layer formed mainly by agglomeration of the plate-like primary particles outside the second low-density layer; Outside the shell layer, a third low-density layer formed mainly by aggregation of the fine primary particles is provided.

In particular, in the nickel-manganese-cobalt-containing composite hydroxide of the present invention, the core, the high-density layer, and the outer shell layer have a nickel ratio, which is the atomic ratio of nickel to the total of nickel, manganese, and cobalt. A first low density layer, a second low density layer, and a third low density layer having a composition with a high nickel ratio greater than 0.4, wherein the nickel ratio is greater than 0.1 and 0.4. It has a low nickel ratio composition of 4 or less.

The average particle diameter MV of the secondary particles is in the range of 4 μm to 11 μm, and [(d90−d10)/average particle diameter MV], which is an index showing the spread of the particle size distribution of the secondary particles, is 0. 0.65 or less is preferred.

The radius of the central portion is in the range of 20% to 40% of the particle size of the secondary particles, and the thickness of the first low density layer is 3% to 15% of the particle size of the secondary particles. range, the thickness of the high-density layer is in the range of 2% to 10% of the particle size of the secondary particles, and the thickness of the second low-density layer is in the range of the particle size of the secondary particles. In the range of 2% to 10%, the thickness of the outer shell layer is in the range of 2% to 10% of the particle size of the secondary particles, and the thickness of the third low-density layer is in the range of the second It is preferably in the range of 2% to 10% of the particle size of the secondary particles.

It is preferable that the plate-like primary particles have a particle size in the range of 0.3 μm to 3 μm, and the fine primary particles have a particle size in the range of 0.01 μm to 0.3 μm.

The _nickel -manganese- _cobalt -containing composite hydroxide has the general formula (A): _NixMnyCozMt ( _OH ) _2+a (x+y+z+t=1, 0.4≤x≤0.70, 0.15≤y≤ 0.4, 0.15≦z≦0.3, 0≦t≦0.1, 0≦a≦0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo , Hf, Ta, and W).

In the method for producing a nickel-manganese-cobalt-containing composite hydroxide according to the second aspect of the present invention, an aqueous raw material solution containing at least a transition metal and an aqueous solution containing an ammonium ion donor are supplied into a reaction vessel to react. A step of forming an aqueous solution and obtaining a nickel-manganese-cobalt-containing composite hydroxide by a crystallization reaction is provided. In the step of obtaining the nickel-manganese-cobalt-containing composite hydroxide, the concentration of ammonium ions in the reaction aqueous solution is controlled within the range of 3 g/L to 25 g/L.

In the method for producing a nickel-manganese-cobalt-containing composite hydroxide of the present invention, nucleation is suppressed by controlling the pH value of the reaction aqueous solution at a liquid temperature of 25° C. in the range of 12.0 to 14.0. The nucleation step to be performed, and the pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step, at a liquid temperature of 25 ° C., is lower than the pH value of the nucleation step and is 10.5 to 12.0. and a grain growth step of growing the nuclei by controlling the range of

In the method for producing a nickel-manganese-cobalt-containing composite hydroxide of the present invention, (1) the reaction atmosphere in the first stage (initial stage) of the nucleation step and the grain growth step is a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less. (2) after the first stage of the grain growth step, the reaction atmosphere is switched from the non-oxidizing atmosphere to an oxidizing atmosphere having an oxygen concentration of more than 5% by volume, and the grain growth is (3) switching the reaction atmosphere from the oxidizing atmosphere to the non-oxidizing atmosphere as a third step of the grain growth process; (4) then reacting (5) further switching the reaction atmosphere from the oxidizing atmosphere to the non-oxidizing atmosphere; (6) Finally, the reaction atmosphere is switched from the non-oxidizing atmosphere to the oxidizing atmosphere, which is the sixth stage of the grain growing process .

In particular, in the method for producing a nickel-manganese-cobalt-containing composite hydroxide of the present invention, the raw material aqueous solution supplied in the first, third, and fifth stages of the nucleation step and the particle growth step contains nickel having a high nickel ratio composition in which the atomic ratio of nickel to the sum of , manganese and cobalt is greater than 0.4 and supplied in the second, fourth and sixth stages of the grain growth process The raw material aqueous solution to be used has a low nickel ratio composition in which the nickel ratio is more than 0.1 and not more than 0.4.

Further, the switching of the reaction atmosphere is defined by the ratio of the amount of metal added at each stage to the total amount of metal added in the grain growth process, and the crystallization at each stage for the entire grain growth process. Regarding the reaction rate, the first stage is 8% to 20%, the second stage is 2% to 20%, the third stage is 12% to 40%, the fourth stage is 3% to 40%, and the fourth stage is 3% to 40%. It is preferable to set the 5th stage to 10% to 40% and the 6th stage to 2% to 20%.

When switching the reaction atmosphere, it is preferable to introduce the oxidizing gas and the non-oxidizing gas using an air diffuser.

The _nickel -manganese- _cobalt -containing composite hydroxide has the general formula (A): _NixMnyCozMt ( _OH ) _2+a (x+y+z+t=1, 0.4≤x≤0.70, 0.15≤y≤ 0.3, 0.15≦z≦0.4, 0≦t≦0.1, 0≦a≦0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo , Hf, Ta, and W).

A positive electrode active material for a lithium ion secondary battery according to a third aspect of the present invention is a ternary positive electrode active material comprising a lithium-nickel-manganese-cobalt-containing composite oxide, and is formed by aggregation of a plurality of primary particles. composed of secondary particles.

In the positive electrode active material for a lithium ion secondary battery of the present invention, the secondary particles have a porous structure. an aggregated portion existing inside the outer shell portion and formed of the aggregated primary particles and electrically connected to the outer shell portion; and a space dispersedly present in the aggregated portion. and a part.

In particular, in the positive electrode active material for a lithium ion secondary battery of the present invention, the primary particles constituting the outer shell portion and the aggregation portion are all nickel, which is the atomic ratio of nickel to the total of nickel, manganese, and cobalt. A surface layer portion having a composition with a high nickel ratio in which the ratio exceeds 0.4, and the composition is graded to a composition with a low nickel ratio in which the nickel ratio exceeds 0.1 and is 0.4 or less Prepare.

The thickness of the outer shell portion of the secondary particles is preferably in the range of 0.1 μm to 1.0 μm.

The average particle diameter MV of the secondary particles is in the range of 3 μm to 10 μm, and [(d90−d10)/average particle diameter MV], which is an index showing the spread of the particle size distribution of the secondary particles, is 0. .7 or less is preferred.

The tap density of the positive electrode active material is preferably in the range of 1.1 g/cm ³ to 1.8 g/cm ³ .

The BET specific surface area of the positive electrode active material is preferably in the range of 2.0 m ² /g to ^{5.0 m 2} /g.

The positive electrode active material preferably has an oil absorption in the range of 35 ml/100 g to 60 ml/100 g.

The crystallite diameter of the primary particles obtained by using the Scherrer formula from the half-value width of the peak of the (003) plane in X-ray diffraction of the (003) plane of the positive electrode active material is preferably in the range of 300 Å to 1500 Å. .

The positive electrode active material for a lithium ion secondary battery of the present invention has the general formula (B): Li _1+u Ni _{x Mny} Co _{z MtO 2} (−0.05≦u≦0.50, x+y+z+t=1, 0. 4≤x≤0.70, 0.15≤y≤0.4, 0.15≤z≤0.3, 0≤t≤0.1, M is Mg, Ca, Al, Ti, V, Cr , Zr, Nb, Mo, Hf, Ta, and W) and has a hexagonal crystal structure with a layered structure, and is composed of a lithium-nickel-manganese-cobalt-containing composite oxide. is preferred.

A method for producing a positive electrode active material for a lithium ion secondary battery according to a fourth aspect of the present invention includes a mixing step of mixing the nickel-manganese-cobalt-containing composite hydroxide and a lithium compound to form a lithium mixture; A firing step of firing the lithium mixture formed in the mixing step at a temperature in the range of 650° C. to 920° C. in an oxidizing atmosphere having an oxygen concentration of 18% to 100% by volume. .

In the mixing step, the lithium mixture is adjusted so that the ratio of the sum of the number of metal atoms other than lithium contained in the lithium mixture to the number of lithium atoms is 1:0.95 to 1.5. preferably.

It is preferable to further include a heat treatment step of heat-treating the nickel-manganese-cobalt-containing composite hydroxide at a temperature in the range of 105°C to 750°C before the mixing step.

The cathode active material for a lithium ion secondary battery has a general formula (B): Li _1+u Ni _{x Mny} Co _{z MtO 2} (−0.05≦u≦0.50, x+y+z+t=1, 0.4≦ x≦0.70, 0.15≦y≦0.4, 0.15≦z≦0.3, 0≦t≦0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta, and W) and has a hexagonal crystal structure with a layered structure . .

A lithium ion secondary battery according to a fifth aspect of the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte (nonaqueous electrolyte secondary battery), or a positive electrode, a negative electrode, and a solid electrolyte (solid electrolyte secondary battery), characterized in that the positive electrode active material for a lithium ion secondary battery according to the third aspect of the present invention is used as a positive electrode active material used in the positive electrode.

In the positive electrode active material for a lithium ion secondary battery of the present invention, the particle structure of the primary particles constituting the outer shell portion and the aggregation portion constituting the porous structure of the secondary particles has a composition with a high nickel ratio, but at the same time By grading the surface layer portion to a composition with a low nickel ratio, the primary particles themselves constituting the outer shell portion and the agglomerate portion are structured to prevent deterioration due to contact with the electrolyte. For this reason, although the lithium-nickel-manganese-cobalt-containing composite oxide has a high nickel ratio as a whole, it is possible to improve the energy density by increasing the nickel ratio without impairing the characteristics of the positive electrode active material with a porous structure, which is excellent output characteristics. Even if it is intended, it is possible to ensure its durability. This makes it possible to improve the battery performance of the lithium-ion secondary battery in comparison with a conventional positive electrode active material having a porous structure with a uniform composition.

The positive electrode active material having such a structure has a layer structure consisting of a central portion, a first low-density layer, a high-density layer, a second low-density layer, an outer shell layer, and a third low-density layer. Nickel-manganese-cobalt-containing composite oxide having a structure consisting of secondary particles and having a composition with a high nickel ratio in the central part, the high density layer, and the outer shell layer, and a composition with a low nickel ratio in the first to third low density layers. It is possible to manufacture industrially by using the substance as a precursor.

Therefore, by applying the positive electrode active material for lithium ion secondary batteries of the present invention to the positive electrode material of lithium ion secondary batteries for power sources of electric vehicles, compared with the conventional, more excellent durability and , it is possible to provide high output characteristics, so it can be said that its industrial significance is great.

FIG. 1 is a cross-sectional view schematically showing the structure of secondary particles constituting the nickel-manganese-cobalt-containing composite hydroxide of the present invention. FIG. 2 is a chart showing steps for producing the nickel-manganese-cobalt-containing composite hydroxide of the present invention. FIG. 3 is a cross-sectional view schematically showing the structure of secondary particles constituting the lithium-nickel-manganese-cobalt-containing composite oxide, which is the positive electrode active material for lithium ion secondary batteries of the present invention. FIG. 4 is a cross-sectional view schematically showing the structure of primary particles that constitute the secondary particles of FIG. FIG. 5 is a schematic cross-sectional view of a 2032-type coin battery used for battery evaluation. FIG. 6 is a schematic explanatory diagram of an example of impedance evaluation measurement and an equivalent circuit used for analysis.

The present inventors have attempted to increase the nickel ratio in a positive electrode active material comprising a lithium-nickel-manganese-cobalt-containing composite oxide comprising secondary particles of a porous structure, in order to further increase the energy density. and a lithium-nickel-manganese-cobalt-containing composite oxide in which the ratio of manganese to cobalt is 1:1:1, the deterioration of the particle structure progresses more quickly due to contact with the electrolyte, and the durability of the positive electrode active material is improved. is damaged, resulting in an increase in the internal resistance (interfacial resistance of the positive electrode) and a problem of deterioration in output characteristics.

The present inventors have made intensive studies on the above problems of the positive electrode active material having a porous structure. While the primary particles themselves have a composition with a high nickel ratio, the primary particles are provided with a surface layer portion that is graded from a composition with a high nickel ratio to a composition with a low nickel ratio. It has been found that the structure of the secondary particles can be prevented from being destroyed by protecting the secondary particles with the moieties.

In addition, in order to obtain a positive electrode active material having such a structure, in the step of producing a nickel-manganese-cobalt-containing composite hydroxide, which is a precursor thereof, of the layer structure constituting the internal structure of the positive electrode active material, In the step of forming the part, the high-density layer, and the outer shell layer, a raw material aqueous solution having a composition with a high nickel ratio is used, and among the layer structures constituting the internal structure, the first to third layers with sparse particle densities It has been found that the process of forming the low-density layer can be achieved by using a raw material aqueous solution having a composition with a low nickel ratio.

The present invention has been completed based on such findings. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in the order of a nickel-manganese-cobalt-containing composite hydroxide, a method for producing the same, a positive electrode active material, a method for producing the same, and a lithium ion secondary battery.

1. Nickel manganese cobalt containing composite hydroxide (1) Particle structure of nickel manganese cobalt containing composite hydroxide It is a precursor of a positive electrode active material for a battery, and is composed of a plurality of plate-like primary particles and secondary particles formed by agglomeration of fine primary particles smaller than the plate-like primary particles. The secondary particles have rounded mass shapes, including substantially spherical and ellipsoidal shapes.

Secondary particles constituting the composite hydroxide of the present invention, as shown in the conceptual diagram of FIG. A first low-density layer 2 formed by agglomeration of fine primary particles, a high-density layer 3 formed mainly by agglomeration of plate-like primary particles outside the first low-density layer 2, and a high-density Outside the layer 3, a second low-density layer 4 formed mainly by agglomeration of fine primary particles, and on the outside of the second low-density layer 4, a layer formed mainly by agglomeration of plate-like primary particles It comprises a shell layer 5 and a third low-density layer 6 formed outside the outer shell layer 5 mainly by agglomeration of fine primary particles.

The central portion 1, the high-density layer 3, and the outer shell layer 5 are basically composed of plate-like primary particles, but fine primary particles may be contained therein. On the other hand, the first low-density layer 2, the second low-density layer 4, and the third low-density layer 6 are basically composed of fine primary particles. Inclusion is not prohibited. In particular, in the first low-density layer 2 and the second low-density layer 4, a high-density portion formed by aggregation of plate-like primary particles in a low-density portion formed by aggregation of fine primary particles part can be present. More specifically, the first low-density layer 2 is located between the surface of aggregates of plate-shaped primary particles that constitute central portion 1 and the surface of aggregates of plate-shaped primary particles that constitute high-density layer 3. The second low-density layer 4 is formed by depositing aggregates of fine primary particles on the surface of the plate-like primary particles forming the high-density layer 3 and the plate-like surface forming the outer shell layer 5. It is formed by depositing aggregates of fine primary particles between the surfaces of aggregates of primary particles. Since the surface of the plate-like primary particle aggregates is uneven, the first low-density layer 2 and the second low-density layer 4 are substantially both plate-like primary particles and fine primary particles. It may result in a formed structure.

In this case, in the first low-density layer 2 and the second low-density layer 4, part of the plate-like primary particle aggregates of the central portion 1 and part of the plate-like primary particle aggregates of the high-density layer 3 Alternatively, part of the plate-like primary particle aggregates of the high-density layer 3 and part of the plate-like primary particle aggregates of the outer shell layer 5 may be in contact with each other. The third low-density layer 6 only needs to have a structure that covers the entire uneven surface of the outer shell layer 5 .

When the secondary particles having such a structure that constitute the composite hydroxide are fired, the plate-like primary particles having a high nickel ratio composition that constitute the core, the high-density portion, and the outer shell are aggregated. The aggregate constitutes primary particles by sintering, and the first to third low-density layers shrink while maintaining the connection between the primary particles to constitute the first to third low-density layers, low nickel Fine primary particles having a ratio composition are absorbed into the primary particles so as to cover the surfaces of the primary particles. Therefore, in the obtained positive electrode active material, as described later, the outer shell portion in which the primary particles are aggregated in the circumferential direction, the primary particle aggregate portion existing inside the outer shell portion, and the aggregate portion existing between the aggregate portions and a space composed of pores of appropriate size. Between the outer shell portion and the aggregated portion of the primary particles existing inside the outer shell portion, and between the aggregated portions of the primary particles inside each other, there is electrical continuity, and the cross-sectional area of the path is sufficiently secured. As a result of the positive electrode active material having a composition with a high nickel ratio as a whole and being composed of such a porous structure, the internal resistance (positive electrode interfacial resistance) of the positive electrode active material is reduced, and the energy density is high. can be maintained.

In particular, the nickel-manganese-cobalt-containing composite hydroxide of the present invention has such a particle structure, while the core, high-density layer, and outer shell layer have a ratio of nickel to the total of nickel, manganese, and cobalt. It has a high nickel ratio composition in which the nickel ratio, which is an atomic ratio, exceeds 0.4, and the first to third low density layers are low nickel in which the nickel ratio exceeds 0.1 and is 0.4 or less It is characterized by having a ratio composition.

With such a structure, when a composite hydroxide composed of secondary particles having such a structure is fired, the resulting positive electrode active material has as a whole the secondary particles (the outer shell portion and the aggregation portion ) is formed by sintering plate-like primary particles having a composition with a high nickel proportion, which constitute the core, the dense layer, and the outer shell layer. However, during sintering, when the fine primary particles having a composition with a low nickel ratio that constitute the first low-density layer to the third low-density layer are absorbed by the primary particles during firing, the surface layer part Form. Therefore, the primary particles are provided with a surface layer portion that is graded from a composition with a high nickel ratio to a composition with a low nickel ratio, and the primary particles themselves are protected by the surface layer portion. As a result, even if the primary particles come into contact with the electrolyte, their deterioration does not progress due to the protection of the surface layer. Therefore, it becomes possible to effectively protect and maintain the structure of the secondary particles.

In a high nickel ratio composition, the nickel ratio is in the range of greater than 0.4 to 1 or less. The nickel ratio is preferably in the range of more than 0.4 to 0.8 or less, and more preferably in the range of 0.45 to 0.7. If the composition of the layer constituting the primary particles of the positive electrode active material after firing is 0.4 or less, the finally obtained positive electrode active material as a whole cannot have a composition with a high nickel ratio.

On the other hand, in the low nickel ratio composition, the nickel ratio is in the range of more than 0.1 to 0.4 or less. The nickel ratio is preferably in the range of more than 0.1 to 0.38 or less, and more preferably in the range of 0.2 to 0.36. Normally, the nickel ratio is 0.33, that is, the hydroxide is composed of nickel, manganese, and cobalt in a ratio of 1:1:1. If the nickel ratio exceeds 0.4, the protective effect of the primary particles due to the formation of the surface layer portion becomes insufficient. On the other hand, if the nickel ratio is 0.1 or less, there is a possibility that the finally obtained positive electrode active material cannot have a composition with a high nickel ratio as a whole.

In the present invention, the difference between the nickel ratio in the high nickel ratio composition and the nickel ratio in the low nickel ratio composition is preferably 0.10 or more, more preferably 0.15 or more. If the difference in the nickel ratio is less than 0.10, a composition with a high nickel ratio cannot be obtained in the entire positive electrode active material to be obtained, or the effect of suppressing the deterioration of secondary particles is sufficiently obtained. may not be

(2) Average particle size MV
In the composite hydroxide of the present invention, the average particle size MV of the secondary particles is adjusted to the range of 3 μm to 12 μm, preferably 4 μm to 11 μm, more preferably 5 μm to 10 μm. 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 that make up the composite hydroxide within such a range, the average particle size MV of the positive electrode active material having the composite hydroxide as a precursor can be increased to a predetermined value. It is possible to control within a range.

In the present invention, the average particle diameter MV of the secondary particles means the volume-based average particle diameter (MeanVolume Diameter), and for example, it can be obtained from the volume integrated value measured with a laser light diffraction scattering particle size analyzer. can.

(3) Particle size distribution In the secondary particles of the composite hydroxide of the present invention, [(d90-d10)/average particle size MV], which is an index showing the spread of the particle size distribution, is 0.65 or less, preferably 0.65. It is adjusted to be 55 or less, more preferably 0.50 or less.

The particle size distribution of the positive electrode active material is strongly influenced by the particle properties of its precursor, the composite hydroxide. Therefore, when a composite hydroxide containing many fine and coarse particles is used as a precursor, the positive electrode active material also contains many fine and coarse particles. performance, cycle characteristics, and output characteristics cannot be sufficiently improved. On the other hand, if the [(d90−d10)/average particle diameter MV] is adjusted to 0.65 or less at the stage of the composite hydroxide, the positive electrode active material using this as a precursor can be obtained. The particle size distribution can be narrowed, making it possible to avoid the problems described above. However, assuming industrial-scale production, it is not realistic to use a composite hydroxide with an excessively small [(d90-d10)/average particle diameter MV]. Therefore, considering cost and productivity, the lower limit of [(d90-d10)/average particle size MV] is preferably about 0.25.

Note that d10 is the particle size where the volume of each particle 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 is calculated by taking the total volume as 100%) Similarly, d90 accumulates the volume of each particle from the smaller particle size side, and the cumulative volume is 90% of the total volume of all particles. % (when the cumulative curve of the particle size distribution is obtained with the total volume being 100%, the particle size at the point where this cumulative curve is 90%). d10 and d90 can be obtained from volume integrated values measured with a laser beam diffraction scattering particle size analyzer in the same manner as the average particle size MV.

(4) The size of the central portion, and the thicknesses of the first low-density layer, high-density layer, second low-density layer, outer shell layer, and third low-density layer Composite hydroxide of the present invention In the object, each of the size of the center, the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer relative to the size of the secondary particles By appropriately controlling the thickness, the outer shell portion formed by the aggregated primary particles and the outer shell portion present inside the outer shell portion, formed by the aggregated primary particles, and electrically conducting with the outer shell portion Thus, a positive electrode active material is obtained which is composed of secondary particles composed of aggregated portions and space portions dispersedly present in the aggregated portions.

In order to obtain such a structure, first, in the composite hydroxide having the structure of the present invention, the average ratio of the radius of the central portion to the particle size of the secondary particles is preferably in the range of 20% to 40%. , more preferably in the range of 25% to 35%. A first low-density layer, a high-density layer, a second low-density layer, an outer shell layer, and, The thickness of the third low-density layer can be set to an appropriate thickness, and the positive electrode active material thus obtained can have a desired porous structure in which the interior is composed of coherent portions and space portions. When the size of the central portion exceeds the above range, the thickness of the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer in the composite hydroxide Since the thickness cannot be controlled within a predetermined range, the desired porous structure may not be obtained in the obtained positive electrode active material.

Also, the thickness of the first low-density layer is preferably in the range of 3% to 15%, more preferably in the range of 5% to 10%, of the particle size of the secondary particles. The thickness of the high-density layer is preferably in the range of 2% to 10%, more preferably in the range of 4% to 8% of the particle size of the secondary particles. The thickness of the second low-density layer is preferably in the range of 2% to 10%, more preferably in the range of 4% to 8%, of the particle size of the secondary particles. The thickness of the outer shell layer is preferably in the range of 2% to 10%, more preferably in the range of 4% to 8%, of the particle size of the secondary particles. Furthermore, the thickness of the third low-density layer is preferably in the range of 2% to 10%, more preferably in the range of 4% to 8% of the particle size of the secondary particles.

By setting the thicknesses of the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer within the above ranges, the composite hydroxylation of such a structure is obtained. In the positive electrode active material obtained by using a substance as a precursor, an outer shell portion having an appropriate thickness that forms the skeleton of the secondary particles, and an aggregate portion formed inside the outer shell portion, and the secondary particles A structure having appropriately sized spaces (pores) distributed inside is obtained. If the first low-density layer and the second low-density layer are too smaller than the respective ranges, the resulting positive electrode active material does not have a sufficiently large space during firing of the composite hydroxide, and substantially It can be a structure similar to a solid structure. Conversely, if the thicknesses of the first low-density layer and the second low-density layer are too large, the low-density layer does not shrink into a pore structure during firing of the composite hydroxide, and the obtained positive electrode In the active material, for example, there is a structure in which a large gap exists between the central portion, the high-density layer, and the outer shell portion, so that the outer shell portion and the internal aggregated portion are not sufficiently connected or integrated, and the desired Structure may not be obtained. In this case, an electrical conduction path having a sufficient cross-sectional area is not formed between the outer shell portion and the internal agglomerate portion, and the effect of reducing the positive electrode resistance cannot be obtained.

On the other hand, if the thicknesses of the high-density layer and the outer shell layer are too small, the predetermined structure of the secondary particles cannot be maintained during the manufacturing stage or the filling stage of the positive electrode active material, and the particles may be destroyed or inside the secondary particles. There is a possibility that a space of sufficient size may not be formed. On the other hand, if the thicknesses of the high-density layer and the outer shell layer are too large, a space of a sufficient size will not be formed inside the secondary particles during firing of the composite hydroxide, resulting in a sufficient amount of space inside the secondary particles. Infiltration of the proper electrolyte and conductive aid may be insufficient.

If the thickness of the third low-density layer is too small, there is a possibility that the surface layer portion may not be properly formed on the primary particles that constitute the outer shell portion of the positive electrode active material.

The composite hydroxide of the present invention has a structure in which a low-density layer, a high-density layer, a low-density layer, a high-density layer, and a low-density layer are laminated on the outside of the central portion. If this laminated structure is further increased, each low-density layer may not be formed with a sufficient thickness, and the effect of improving the specific surface area may not be obtained sufficiently. On the other hand, in the case of a laminated structure consisting of a low-density layer, a high-density layer, and a low-density layer, in the positive electrode active material obtained, the existence ratio of the space is insufficient, and the desired characteristics such as a sufficient specific surface area and low internal resistance are not achieved. may not be obtained.

In the present invention, as long as each of the central portion, the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer has a predetermined thickness When the composite hydroxide having such a structure is fired, the central portion, the high-density layer, and the outer shell layer are substantially integrated due to sintering shrinkage, and the space portions generated dispersedly inside are An existing structure is obtained. The space existing inside can communicate with the outside through grain boundaries or voids between primary particles forming aggregates. Therefore, in such a structure, the electrical conduction path between the primary particles constituting the secondary particles is sufficiently secured while maintaining the difficulty of collapsing of the overall structure of the positive electrode active material obtained, and the space and As a result of sufficiently ensuring communication with the outside, it is possible to further reduce the positive electrode resistance.

The size of the central portion, and the thicknesses of the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer constitute the composite hydroxide. It is possible to determine the cross section of the secondary particles by observing them with a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM). However, the secondary particles that make up the composite hydroxide have an irregular overall shape, and the shape of each layer is also complicated, so it is not easy to specify the thickness of each layer by SEM observation. Therefore, the size of the core and the thicknesses of the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer herein refer to the composite of the hydroxide manufacturing process, added in a non-oxidizing atmosphere or an oxidizing atmosphere to form the core and each layer, relative to the total amount of metal added during the grain growth process, respectively can be obtained theoretically from the ratio of the metal content of

(5) Primary particles In the composite hydroxide of the present invention, the size of the plate-like primary particles constituting the central portion, the high-density layer, and the outer shell layer, and the fine particles constituting the first to third low-density layers The size of the primary particles is determined by embedding the secondary particles of the composite hydroxide in a resin or the like, making the cross section observable by processing such as a cross section polisher, and then using an SEM such as FE-SEM for the cross section. When they are observed by using them, they differ to such an extent that the difference in structure can be clearly grasped on imaging.

In the composite hydroxide of the present invention, the plate-like primary particles are formed with a size that provides an average particle size in the range of 0.3 μm to 3 μm. Preferably, the plate-like primary particles have an average particle diameter in the range of 0.4 μm to 1.5 μm. When the average particle size of the plate- like primary particles is less than 0.3 μm, volumetric shrinkage of the plate-like primary particles also occurs in a low temperature range in the firing process for producing the positive electrode active material. Since the difference in volume shrinkage between the low-density layer 3, the central portion, the high-density layer and the outer shell layer is small, there is a possibility that a sufficient number of spaces cannot be obtained inside the positive electrode active material. On the other hand, when the average particle size of the plate-like primary particles is larger than 3 μm, in the firing process for producing the positive electrode active material, firing at a higher temperature is required in order to increase the crystallinity of the positive electrode active material. Sintering between the secondary particles constituting the hydroxide progresses, making it difficult to set the average particle size MV and particle size distribution of the positive electrode active material within a predetermined range.

On the other hand, the fine primary particles are formed in a size that can be sufficiently distinguished from the plate-like primary particles by SEM observation or the like. Although it may be difficult to fully grasp the size of the SEM image, the fine primary particles have an average particle size smaller than that of the plate-like primary particles, that is, the average particle size is , 0.01 μm to 0.3 μm, and the difference from the average particle diameter of the plate-like primary particles is 0.1 μm or more. Usually, the average particle size of the fine primary particles has a difference of 0.3 μm or more from the average particle size of the plate-like primary particles. If the average particle size of the fine primary particles is less than 0.01 μm, the thickness of the low-density layer cannot be obtained satisfactorily. On the other hand, when the average particle diameter of the fine primary particles is larger than 0.3 μm, volumetric shrinkage due to heating does not proceed sufficiently during firing in a low temperature range in the firing process for producing the positive electrode active material, resulting in a low density. Since the difference in the amount of volume contraction between the layer and the central portion and the high-density layer becomes small, there is a possibility that a sufficiently large space portion will not be formed inside the secondary particles of the positive electrode active material.

The shape of such fine primary particles cannot be sufficiently grasped even by SEM observation and cannot be specified in some cases. This is because the acicular primary particles have a one-dimensional directionality and can form a structure with many gaps, that is, a structure with low density when the particles are aggregated.

As described above, it is sufficient that the sizes of the fine primary particles and the plate-like primary particles are different enough that the difference between the layers or portions formed by the aggregation can be understood by SEM observation, and it is necessary to specifically measure them. no. In particular, fine primary particles may be so small that their shape cannot be fully grasped. Both the shape and size of the fine primary particles and plate-like primary particles can be determined as follows when SEM observation is possible. That is, the maximum outer diameter (major axis diameter) of 10 or more fine primary particles or plate-shaped primary particles present in the cross section of the secondary particles is measured, the average value is obtained, and this value is It is defined as the particle size of fine primary particles or plate-like primary particles. Next, for 10 or more secondary particles, the particle sizes of fine primary particles and tabular primary particles are determined in the same manner. Finally, by averaging the particle sizes obtained for these secondary particles, the average particle size of fine primary particles or plate-like primary particles in the entire composite hydroxide is determined.

(4) Composition The composite hydroxide of the present invention is a precursor of a ternary positive electrode active material composed of a lithium-nickel-manganese-cobalt-containing composite oxide (NMC) containing at least nickel, manganese, and cobalt as transition metals. is the body. The composition is not limited as long as it has the above-described particle structure, average particle size, and particle size distribution. However, since the present invention is particularly preferably applied to a positive electrode active material having a composition with a high nickel ratio, the composite hydroxide as a whole has a nickel ratio, which is the atomic ratio of nickel to the total of nickel, manganese, and cobalt. is greater than 0.4.

In particular, the composite hydroxide of the present invention has the general formula (A): _NixMnyCozMt ( _OH ) _{2 + a} (x+y+z+t=1, 0.4≤x≤0.70, 0.15≤y≤ 0.4, 0.15≦z≦0.3, 0≦t≦0.1, 0≦a≦0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo , Hf, Ta, and W). By using a composite hydroxide having such a composition as a precursor, it is possible to easily obtain the positive electrode active material represented by the general formula (B) described later, and it is possible to achieve higher battery performance. .

In addition, in the composite hydroxide represented by the general formula (A), the composition range and critical significance of nickel, manganese, cobalt, and the additive element M constituting this are represented by the general formula (B). is similar to that of the positive electrode active material. Therefore, description of these matters is omitted here.

2. Method for Producing Nickel-Manganese-Cobalt-Containing Composite Hydroxide (1) Crystallization Reaction The method for producing a composite hydroxide of the present invention includes a raw material aqueous solution containing at least a transition metal and an ammonium ion donor in a reaction vessel. In this method, a reaction aqueous solution is formed by supplying an aqueous solution, and a composite hydroxide that serves as a precursor of a positive electrode active material is produced by a crystallization reaction.

In the method for producing a composite hydroxide of the present invention, the crystallization reaction is clearly separated into two stages, a nucleation step in which nucleation is mainly performed and a grain growth step in which grains are mainly grown. By adjusting the precipitation conditions, particularly in the particle growth step, while continuing to supply the raw material aqueous solution, by switching the reaction atmosphere and switching the composition of the raw material aqueous solution, the above-described grain structure, average particle diameter MV, And, it makes it possible to efficiently obtain a composite hydroxide having a particle size distribution.

The method for producing a composite hydroxide of the present invention includes a nucleation step in which the crystallization reaction is adjusted to a pH value in the range of 12.0 to 14.0 at a liquid temperature of 25° C. of the reaction aqueous solution to generate nuclei. , The pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step at a liquid temperature of 25 ° C. is controlled to be lower than the pH value of the nucleation step and 10.5 to 12.0. A clear distinction is made between two stages of the grain growth process, ie, growing nuclei.

In addition, before starting the nucleation process or at the time of starting the nucleation process, by circulating an inert gas in the reaction tank, the reaction atmosphere at the beginning of the nucleation process and the particle growth process has an oxygen concentration of 5% by volume or less. While adjusting the atmosphere to a non-oxidizing atmosphere, in the particle growth step, the reaction atmosphere is changed from the non-oxidizing atmosphere to an oxygen concentration exceeding 5% by volume by introducing the atmosphere gas while continuing to supply the raw material aqueous solution. After switching to the oxidizing atmosphere, by introducing the non-oxidizing gas again, the reaction atmosphere is switched from the oxidizing atmosphere to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less. and switching from a non-oxidizing atmosphere to an oxidizing atmosphere.

More specifically, as shown in FIG. 2, in the method for producing a composite hydroxide of the present invention, (1) in the first stage (initial stage) of the nucleation step and the particle growth step, the reaction atmosphere has an oxygen concentration of (2) after the first stage of the grain growth process, the reaction atmosphere is switched from a non-oxidizing atmosphere to an oxidizing atmosphere with an oxygen concentration of more than 5% by volume; (3) switching the reaction atmosphere from an oxidizing atmosphere to a non-oxidizing atmosphere to form a third stage of the particle growth process; (4) changing the reaction atmosphere to a non-oxidizing atmosphere. (5) Further, the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere to perform the fifth stage of the particle growth process, ( 6) Next, the reaction atmosphere is switched from the non-oxidizing atmosphere to the oxidizing atmosphere, which is the sixth stage of the grain growth process.

At that time, the switching of the reaction atmosphere is defined as the ratio of the amount of metal added in each stage to the total amount of metal added in the grain growth process, and the amount of crystallization reaction in each stage for the entire grain growth process. It is preferable to set the ratio as follows. That is, the first stage is in the range of 8% to 20%, the second stage is in the range of 2% to 20%, the third stage is in the range of 12% to 40%, and the fourth stage is in the range of 3% to 40%. It is preferable that the fifth stage be 10% to 40% and the sixth stage be 2% to 20%.

Basically, by switching the reaction atmosphere as described above, secondary particles of the desired multilayered composite hydroxide can be obtained.

Further, in the method for producing a composite hydroxide of the present invention, the composition of the raw material aqueous solution is switched during the crystallization reaction. Specifically, the nickel ratio, which is the atomic ratio of nickel to the total of nickel, manganese, and cobalt, as the raw material aqueous solution supplied in the first, third, and fifth stages of the nucleation process and the grain growth process A raw aqueous solution having a composition with a high nickel ratio is used, in which σ is greater than 0.4. On the other hand, as the raw material aqueous solution supplied in the second, fourth, and sixth stages of the grain growth process, the raw material aqueous solution has a low nickel ratio composition in which the nickel ratio exceeds 0.1 and is 0.4 or less. Use By switching the raw material aqueous solution in this way, the composition of the plate-shaped primary particles constituting the central portion, the high-density layer, and the outer shell layer can be made a composition with a high nickel ratio exceeding 0.4, The composition of fine primary particles constituting the first to third low-density layers can be a low nickel ratio composition in which the nickel ratio exceeds 0.1 and is 0.4 or less.

The method for producing the composite hydroxide of the present invention is not limited by its composition as long as the structure, average particle size MV, and particle size distribution described above can be realized, but it is represented by the general formula (A) It can be suitably applied to composite hydroxides.

The crystallization step will be described in more detail below.

[Nucleation step]
In the nucleation step, first, a transition metal compound as a raw material in this step is dissolved in water to prepare a raw material aqueous solution. At the same time, 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 measured at a liquid temperature of 25° C. is 12.0 to 14.0, and the ammonium ion concentration is 3 g/g/. Prepare a pre-reaction aqueous solution that is L-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.

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 the aqueous solution for nucleation is within the range described above, nucleation takes place preferentially with little growth of nuclei in the nucleation step. In the nucleation step, the pH value and the concentration of ammonium ions in the aqueous solution for nucleation change with nucleation. It is necessary to control the pH in the range of 12.0 to 14.0 and the ammonium ion concentration in the range of 3 g/L to 25 g/L on a °C basis.

In the nucleation step, it is necessary to circulate an inert gas in the reaction vessel to adjust the reaction atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. It is usually preferable to adjust the reaction atmosphere before starting the supply of the raw material aqueous solution. As a result, the aggregation portion is sufficiently formed inside the positive electrode active material having the composite hydroxide as a precursor, and it is possible to suppress the decrease in particle density due to the formation of the space portion.

In the nucleation step, new nuclei are continuously generated by supplying an aqueous solution containing a raw material aqueous solution, an alkaline aqueous solution and an ammonium ion donor to the nucleating aqueous solution. Then, when a predetermined 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, but in order to obtain secondary particles of composite hydroxide with a narrow particle size distribution, it is necessary to add It is preferably 0.1 atomic % to 2 atomic %, more preferably 0.1 atomic % to 1.5 atomic %, relative to the metal element in the contained metal compound. The reaction time in the nucleation step is usually about 0.2 to 5 minutes.

[Particle growth step]
After completion of the nucleation step, the pH value of the aqueous solution for nucleation in the reaction tank is adjusted to 10.5 to 12.0 based on the liquid temperature of 25° C. to form the aqueous solution for particle growth, which is the reaction aqueous solution in the particle growth step. do. The pH value can also be adjusted by stopping the supply of the alkaline aqueous solution. is preferably adjusted. Specifically, after stopping the supply of all the aqueous solution, it is preferable to adjust the pH value by supplying the same inorganic acid as the acid that constitutes the metal compound as a raw material to the aqueous solution for nucleation.

Next, supply of the raw material aqueous solution is resumed while stirring the particle growth aqueous solution. 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 generated, the nuclei (particles) grow, and the secondary particles of the composite hydroxide having a predetermined particle size is formed. Also in the particle growth process, the pH value and ammonium ion concentration of the aqueous solution for particle growth change as the particles grow. Therefore, the alkaline aqueous solution and the ammonia aqueous solution are supplied at appropriate times to maintain the pH value and the ammonium ion concentration within the above ranges. It is necessary to

In particular, in the method for producing a composite hydroxide of the present invention, in the middle of the particle growth step, the supply of two types of raw material aqueous solutions is alternately switched, and two types of atmosphere gases are introduced while continuing the supply. Thus, the reaction atmosphere is switched from a non-oxidizing atmosphere to an oxidizing atmosphere with an oxygen concentration of more than 5% by volume, or from this non-oxidizing atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. perform an operation.

In the particle growth step, an inert gas and/or an oxidizing gas is passed through the reaction aqueous solution in the reaction vessel using an air diffuser to switch from an oxidizing atmosphere to a non-oxidizing atmosphere, or It is preferable to quickly switch from the oxidizing atmosphere to the oxidizing atmosphere. As for the method of supplying the inert gas and/or oxidizing gas to the reaction aqueous solution in the reaction vessel, it is possible to supply the space in the reaction vessel that is in contact with the reaction aqueous solution. / Alternatively, it is preferable to adopt a method of directly supplying the oxidizing gas into the reaction aqueous solution. This can reduce the atmosphere switching time, and the size of the center, the first low density layer, the high density layer, the second low density layer, the outer shell layer, and the third low density layer. It becomes possible to set the thickness appropriately.

In addition, in the grain growth step, at the same time as the first non-oxidizing atmosphere is switched to the first oxidizing atmosphere (at the time of transition from the first stage to the second stage), the raw material aqueous solution is changed to a raw material having a composition with a high nickel ratio. The aqueous solution is switched to a raw aqueous solution having a composition with a low nickel percentage. In addition, at the same time as the first oxidizing atmosphere is switched to the second non-oxidizing atmosphere (at the time of transition from the second stage to the third stage), the raw material aqueous solution having a composition with a low nickel ratio is changed to a high nickel ratio. Switch to a raw aqueous solution having a composition of the nickel ratio. Next, at the same time as the second non-oxidizing atmosphere is switched to the second oxidizing atmosphere (at the time of transition from the third stage to the fourth stage), the raw material aqueous solution is again changed to a composition with a high nickel ratio. switch from an aqueous raw material solution having a low nickel ratio composition to an aqueous raw material solution having a low nickel ratio composition. At the same time as the second oxidizing atmosphere is switched to the third non-oxidizing atmosphere (during the transition from the fourth stage to the fifth stage), the raw material aqueous solution is changed from the raw material aqueous solution having a low nickel ratio composition to a high nickel ratio composition. Switch to a raw aqueous solution having a composition of the nickel ratio. Finally, at the same time as the third non-oxidizing atmosphere is switched to the third oxidizing atmosphere (at the time of transition from the fifth stage to the sixth stage), the raw material aqueous solution is again changed to a composition with a high nickel ratio. switch from an aqueous raw material solution having a low nickel ratio composition to an aqueous raw material solution having a low nickel ratio composition.

In this case, the composition of the primary particles constituting each layer is appropriately controlled by providing a supply route for two raw material aqueous solutions into the reaction vessel and rapidly switching the raw material aqueous solution supplied into the reaction vessel. becomes possible.

In such a method for producing a composite hydroxide, metal ions precipitate as nuclei or primary particles in the nucleation step and the particle growth step. Therefore, the ratio of the liquid component to the metal component in the nucleation aqueous solution and the particle growth aqueous solution is increased. As a result, the concentration of the raw material aqueous solution is apparently lowered, and particularly in the particle growth step, the growth of the secondary particles of the composite hydroxide may be stagnated. Therefore, in order to suppress an increase in the liquid component, it is preferable to discharge a part of the liquid component of the aqueous solution for particle growth to the outside of the reaction tank during the particle growth process after the end of the nucleation process. Specifically, the supply and agitation of the raw material aqueous solution, the alkaline aqueous solution, and the aqueous solution containing the ammonium ion donor are temporarily stopped, and the nuclei and composite hydroxides in the particle growth aqueous solution are allowed to settle, and the supernatant of the particle growth aqueous solution is It is preferred to drain the liquid. By such an operation, the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth can be increased, so that the stagnation of particle growth can be prevented, and the particle size distribution of the secondary particles of the obtained composite hydroxide can be adjusted to a suitable range. In addition, the density of the secondary particles as a whole can be improved.

[Particle size control of secondary particles of composite hydroxide]
The particle size of the secondary particles of the composite hydroxide obtained as described above depends on the time of the particle growth process and the nucleation process, the pH value of the nuclear generation aqueous solution and the particle growth aqueous solution, and the supply amount of the raw material aqueous solution. can be controlled. For example, by performing the nucleation step at a high pH value or by lengthening the time of the particle generation step, the amount of the metal compound contained in the supplied raw material aqueous solution is increased, the amount of nuclei generated is increased, and the The particle size of the secondary particles of the composite hydroxide can be reduced. Conversely, by suppressing the amount of nuclei generated in the nucleation step, the secondary particles of the resulting composite hydroxide can have a larger particle size.

[Another Embodiment of Crystallization Reaction]
In the method for producing a composite hydroxide of the present invention, an aqueous solution for component adjustment adjusted to a pH value and an ammonium ion concentration suitable for the particle growth step is prepared separately from the aqueous solution for nucleation. , an aqueous solution for nucleation after the nucleation step, preferably an aqueous solution for nucleation after the nucleation step from which part of the liquid component has been removed is added and mixed, and this is used as an aqueous solution for particle growth, and the particle growth step may be performed.

In this case, since the nucleation step and the particle growth step can be separated more reliably, the reaction aqueous solution in each step can be controlled to an optimum state. In particular, since the pH value of the aqueous solution for particle growth can be controlled within the optimum range from the start of the particle growth step, the particle size distribution of the resulting secondary particles of the composite hydroxide can be made narrower. .

(2) Aqueous solution to be supplied In the method for producing a composite hydroxide of the present invention, a raw material aqueous solution containing at least nickel, manganese and cobalt and an aqueous solution containing an ammonium ion donor are supplied to the reaction vessel to produce a reaction aqueous solution. A complex hydroxide is obtained by a crystallization reaction while adjusting the pH value of the reaction aqueous solution to a predetermined range with a pH adjuster.

a) Raw material aqueous solution In the present invention, the ratio of the metal elements contained in the two raw material aqueous solutions is generally the composition ratio of the resulting composite hydroxide. Therefore, it is necessary to appropriately adjust the content of the metal element in each of the two raw material aqueous solutions according to the desired composition of the composite hydroxide, in addition to changing the nickel ratio.

For example, when trying to obtain the composite hydroxide represented by the general formula (A) described above, the ratio of the metal elements contained in the two raw material aqueous solutions is changed to Ni:Mn:Co:M=x: y: z; t (however, x + y + z + t = 1, 0.4 ≤ x ≤ 0.70, 0.15 ≤ y ≤ 0.4, 0.15 ≤ z ≤ 0.3, 0 ≤ t ≤ 0.1) while adjusting the nickel ratio contained in one raw material aqueous solution to a composition with a high nickel ratio exceeding 0.4, and the nickel ratio contained in the other raw material aqueous solution to 0.1 It is necessary to adjust the composition to a low nickel ratio of 0.4 or less.

More specifically, the nickel ratio of the raw material aqueous solutions supplied in the first stage, the third stage, and the fifth stage is set to a range exceeding 0.4 and 1 or less, preferably exceeding 0.4 It should be in the range of 0.8 or less, more preferably in the range of 0.45 to 0.7. On the other hand, the nickel ratio of the raw material aqueous solutions supplied in the second, fourth, and sixth stages is in the range of more than 0.1 to 0.4, preferably more than 0.1 to 0.4. It should be in the range of 38 or less, more preferably in the range of 0.2 to 0.36. For example, when the ratio of nickel, manganese, and cobalt in the raw material aqueous solutions supplied in the first, third, and fifth stages is 5:3:2 to 6:3:1, the second stage, The ratio of nickel:manganese:cobalt in the raw material aqueous solutions supplied in the fourth stage and the sixth stage can be 3.5-4:3-3.5:3-3.5.

When the additive element M is introduced in a separate process, the additive element M should not be contained in the raw material aqueous solution. Further, in the nucleation step and the grain growth step, it is possible to change the presence or absence of addition of the additive element M, or the content ratio of the transition metal and the additive element M.

The transition metal compound for preparing the raw material aqueous solution is not particularly limited, but it is preferable to use water-soluble nitrates, sulfates, chlorides, etc. from the viewpoint of ease of handling. From the viewpoint of preventing contamination, it is particularly preferable to suitably use sulfate.

Further, the additive element M (M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) is added to the composite hydroxide. When it is contained, the compound for supplying the additional element M is preferably a water-soluble compound, such as magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, and 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 concentration of the raw material aqueous solution is preferably 1 mol/L to 2.6 mol/L, more preferably 1.5 mol/L to 2.2 mol/L, in terms of the total concentration of metal compounds. If the concentration of the raw material aqueous solution is less than 1 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 saturated concentration at normal temperature, and crystals of each metal compound may re-precipitate and clog pipes and the like.

The metal compound described above does not necessarily have to be supplied to the reaction tank as an aqueous raw material solution. For example, when performing a crystallization reaction using a metal compound that reacts to produce a compound other than the desired compound when mixed, 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 an aqueous solution of individual metal compounds.

Further, the supply amount of the raw material aqueous solution is such that the concentration of the product in the particle growth aqueous solution is preferably 30 g/L to 200 g/L, more preferably 80 g/L to 150 g/L at the end of the particle growth step. make it If the product concentration is less than 30 g/L, the aggregation of primary particles may be insufficient. On the other hand, if it exceeds 200 g/L, the aqueous metal salt solution for nucleation or the aqueous metal salt solution for particle growth may not sufficiently diffuse into the reaction tank, resulting in uneven particle growth.

b) Alkaline aqueous solution The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. Although the alkali metal hydroxide can be added directly to the reaction aqueous solution, it is preferable to add it as an aqueous solution for 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 regulating the concentration of the alkali metal aqueous solution within such a range, it is possible to suppress the amount of solvent (water amount) supplied to the reaction system and prevent the pH value from locally increasing at the addition position. , it is possible to efficiently obtain secondary particles of composite hydroxide with a narrow particle size distribution.

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.

c) Aqueous solution containing ammonium donor The aqueous solution containing ammonium ion donor is also not particularly limited, and for example, ammonia water or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate or ammonium fluoride can be used. can be done.

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 regulating the concentration of ammonia water within such a range, the loss of ammonia due to volatilization can be minimized, and thus 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.

[pH value]
In the method for producing a composite hydroxide of the present invention, the pH value of the reaction aqueous solution at a liquid temperature of 25° C. is in the range of 12.0 to 14.0 in the nucleation step, and 10.5 in the particle growth step. It is necessary to control in the range of ~12.0. In any step, it is preferable to control the fluctuation range of the pH value during the crystallization reaction 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 secondary particles of composite hydroxide with a narrow particle size distribution. The pH value of the reaction aqueous solution can be measured with a pH meter.

a) Nucleation step In the nucleation step, the pH value of the reaction aqueous solution (nucleation aqueous solution) is 12.0 to 14.0, preferably 12.3 to 13.5, based on the liquid temperature of 25 ° C. Preferably, it is necessary to control in the range of 12.5-13.3. As a result, it is possible to suppress the growth of nuclei and give priority to nucleation, so that the nuclei generated in this step can be homogeneous and have a narrow particle size distribution. On the other hand, if the pH value is less than 12.0, the growth of nuclei (particles) proceeds along with the nucleation, so that the secondary particles of the resulting composite hydroxide become non-uniform in particle size and the particle size distribution deteriorates. 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.

b) Particle Growth Step In the particle growth step, the pH value of the reaction aqueous solution (particle growth aqueous solution) is 10.5 to 12.0, preferably 11.0 to 12.0, more preferably 11.0 to 12.0, based on a liquid temperature of 25°C. must be controlled within the range of 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 secondary particles of the obtained composite hydroxide can be made uniform and have a narrow particle size distribution. On the other hand, if the pH value 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 reaction aqueous solution. and productivity suffers. On the other hand, if the pH value exceeds 12.0, the amount of nuclei generated during the particle growth step increases, the secondary particles of the composite hydroxide obtained have non-uniform particle sizes, 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 secondary particles of composite hydroxide having 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 nucleus grows and good secondary particles of composite hydroxide 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.

[Reaction atmosphere]
The secondary particle structure of the composite hydroxide of the present invention is formed by controlling the pH value of the reaction aqueous solution in the nucleation step and the particle growth step as described above, and by controlling the reaction atmosphere in these steps. be. Therefore, in the method for producing a composite hydroxide of the present invention, control of the reaction atmosphere as well as control of the pH value in each step is of great significance.

In such control of the reaction atmosphere, the fine primary particles constituting the first to third low-density layers are usually plate-like and/or needle-like, but depending on the composition of the composite hydroxide, they may be rectangular parallelepiped-like. , an elliptical shape, and a pyramidal shape. In this respect, the same applies to the plate-like primary particles that constitute the central portion, the high-density layer, and the outer shell layer. Therefore, in the method for producing a composite hydroxide of the present invention, it is necessary to appropriately control the reaction atmosphere in each stage according to the desired composition of the composite hydroxide.

a) Non-Oxidizing Atmosphere In the production method of the present invention, the reaction atmosphere in the step of forming the core of the secondary particles of the composite hydroxide, the high-density layer, and the outer shell layer is a non-oxidizing atmosphere. Specifically, by introducing a non-oxidizing gas such as an inert gas, the oxygen concentration in the reaction atmosphere is 5% by volume or less, preferably 2% by volume or less, more preferably 1% by volume or less. It is necessary to control the mixed atmosphere of oxygen and inert gas so as to create an oxidizing atmosphere. As a result, while suppressing unnecessary oxidation, the nuclei generated in the nucleation process can be grown to a certain range, so that the core, high-density layer, and outer shell layer of the secondary particles of the composite hydroxide can have a structure in which plate-like primary particles are aggregated.

b) Oxidizing Atmosphere On the other hand, in the step of forming the first to third low-density layers of secondary particles of composite hydroxide, the reaction atmosphere is controlled to be an oxidizing atmosphere. Specifically, the oxygen concentration in the reaction atmosphere is controlled so as to exceed 5% by volume, preferably 10% by volume or more, more preferably an atmospheric atmosphere (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere to such a range, particle growth is suppressed and the average particle size of the primary particles is in the range of 0.01 μm to 0.3 μm. and the first to third low-density layers having a sufficient difference in density from the outer shell layer.

The upper limit of the oxygen concentration in the reaction atmosphere at this stage is not particularly limited. It may not be the size. Therefore, the oxygen concentration is preferably 30% by volume or less.

c) Switching Reaction Atmosphere In the particle growth step, it is necessary to control the atmosphere as described above so that the composite hydroxide having the desired particle structure is formed.

In the method for producing a composite hydroxide of the present invention, when the atmosphere gas is directly supplied into the reaction aqueous solution using an air diffuser, the reaction atmosphere, that is, the dissolved oxygen content in the reaction aqueous solution that is the reaction field, is Changes without delay in response to changes in oxygen concentration in the tank. Therefore, the atmosphere switching time can be confirmed by measuring the oxygen concentration in the reaction vessel. On the other hand, when the atmosphere gas is supplied to the space in contact with the reaction aqueous solution in the reaction vessel, a time lag occurs between the change in the dissolved oxygen amount in the reaction aqueous solution and the change in the oxygen concentration in the reaction vessel. Until the change in oxygen concentration stabilizes, the dissolved oxygen amount in the reaction aqueous solution cannot be immediately confirmed as a correct value. It is possible to Thus, in any case, the atmosphere switching time obtained based on the oxygen concentration in the reaction vessel can be used as the switching time for the amount of oxygen dissolved in the reaction aqueous solution, which is the reaction field. Based on the oxygen concentration in the tank, the reaction atmosphere can be appropriately controlled over time.

In the present invention, the time required for switching the atmosphere is about 1% to 2% of the entire grain growth process. This time is also common when switching from a non-oxidizing atmosphere to an oxidizing atmosphere or from an oxidizing atmosphere to a non-oxidizing atmosphere. Therefore, although it is possible to strictly control the atmosphere switching time independently, it is usually sufficient to include it in the non-oxidizing atmosphere or oxidizing atmosphere time after the atmosphere switching.

More specifically, the crystallization reaction in a non-oxidizing atmosphere in the first stage (initial stage) of the grain growth stage preferably accounts for 10% to 20% of the total grain growth process time, more preferably The range is from 10% to 18%.

The crystallization reaction in the oxidizing atmosphere in the second stage (including the time for switching from the non-oxidizing atmosphere to the oxidizing atmosphere) is preferably in the range of 2% to 20%, more than It is preferably in the range of 3% to 15%. However, the ratio of the entire crystallization reaction in the oxidizing atmosphere in the second stage, the fourth stage, and the sixth stage is preferably within the range of 5% to 50%, more preferably within the range of 6% to 40%. to

The crystallization reaction in the non-oxidizing atmosphere in the third stage (including the switching time from the oxidizing atmosphere to the non-oxidizing atmosphere) is preferably in the range of 12% to 40% of the total grain growth process time. More preferably in the range of 14% to 34%, the second switching to the oxidizing atmosphere is in the range of 3% to 40% of the entire grain growth process from the start of the grain growth process, preferably It is carried out in the range of 4% to 25%.

The crystallization reaction in the oxidizing atmosphere in the fourth stage (including the time for switching from the non-oxidizing atmosphere to the oxidizing atmosphere) preferably accounts for the ratio of the crystallization reaction in the second stage to the entire grain growth process time. is 1.2 times to 2.5 times, more preferably 1.5 times to 2.0 times, preferably in the range of 3% to 40%, more preferably in the range of 4% to 25%.

The crystallization reaction in the non-oxidizing atmosphere in the fifth stage (including the switching time from the oxidizing atmosphere to the non-oxidizing atmosphere) is preferably in the range of 10% to 40% of the total grain growth process time, More preferably, it is in the range of 25% to 35% to form a sufficient skeleton of the outer shell.

The crystallization reaction in the oxidizing atmosphere in the sixth stage (including the switching time from the non-oxidizing atmosphere to the oxidizing atmosphere) is preferably in the range of 2% to 20%, more than It is preferably in the range of 3% to 15%. After a predetermined time has elapsed, the crystallization reaction is finally terminated.

The ratio of the crystallization reaction in each stage is defined by the ratio of the amount of metal added in each stage to the total amount of metal added in the grain growth process. In actual operation, by supplying the raw material aqueous solution constantly and making the amount of added metal constant, each crystallization reaction time is set at a predetermined ratio with respect to the entire grain growth process time. can be controlled to be

d) Switching method Switching of the reaction atmosphere during the crystallization step is performed by circulating the atmosphere gas in the reaction tank or by inserting a conduit having an inner diameter of about 1 mm to 50 mm into the reaction aqueous solution and bubbling the atmosphere gas. is common. In this case, since it takes a long time to switch the reaction atmosphere, it is necessary to stop the supply of the raw material aqueous solution during the switching. Unless the supply of the raw material aqueous solution is stopped, a gentle density gradient may be formed inside the composite hydroxide particles. In this case, especially the formation of the first low density layer and the second low density layer may be insufficient.

On the other hand, when the reaction atmosphere is switched by an air diffuser, the air diffuser is composed of a conduit having many fine holes on its surface, and can release many fine gases (bubbles) into the liquid, so that the reaction time can be reduced in a short time. It is possible to switch the reaction atmosphere with . Therefore, it is not necessary to stop the supply of the raw material aqueous solution when switching the reaction atmosphere, and the production efficiency can be improved. In this case, even if the rate of crystallization reaction in the oxidizing atmosphere becomes short, it is possible to sufficiently form the low-density layer.

As the air diffuser, it is preferable to use a ceramic diffuser that has excellent resistance in a high pH environment. In addition, the smaller the pore diameter of the diffuser tube, the more minute air bubbles can be released, so that the reaction atmosphere can be switched with high efficiency. It is preferable to use an air diffuser with a pore size of 100 μm or less, more preferably 50 μm or less.

(4) Ammonium Ion Concentration The ammonium ion concentration in the reaction aqueous solution is preferably maintained at a constant value within the range of 3 g/L to 25 g/L, more preferably 5 g/L to 20 g/L. 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 metal ions cannot be maintained constant, and the reaction aqueous solution tends to gel, resulting in a It becomes difficult to obtain secondary particles of composite hydroxide 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. The ammonium ion concentration of the reaction aqueous solution can be measured with an ion meter.

Note that if the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ions fluctuates, and uniform secondary particles of the composite hydroxide 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.

(5) 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 the particle growth step. If the reaction temperature is less than 20°C, nucleation is likely to occur due to the low solubility of the reaction aqueous solution, and it is difficult to control the average particle size MV and particle size distribution of the resulting composite hydroxide secondary particles. becomes. 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.

(6) Coating step In the method for producing a composite hydroxide of the present invention, by adding a compound containing the additive element M to the raw material aqueous solution, the secondary compound hydroxide in which the additive element M is dispersed inside the particles particles can be obtained. However, when trying to obtain the effect of adding the additive element M with a smaller additive amount, the surface of the secondary particles of the composite hydroxide is coated with a compound containing the additive element M after the particle growth step. A coating step is preferably carried out.

The coating method is not particularly limited as long as the secondary particles of the composite hydroxide can be coated with the compound containing the additive element M. For example, after slurrying the composite hydroxide and controlling its pH value within a predetermined range, an aqueous solution (aqueous solution for coating) in which a compound containing the additional element M is dissolved is added to form secondary particles of the composite hydroxide. By precipitating the compound containing the additive element M on the surface, the secondary particles of the composite hydroxide coated with the compound containing the additive element M can be obtained. In this case, instead of the coating aqueous solution, an alkoxide solution of the additive element M may be added to the slurried composite hydroxide. Alternatively, instead of slurrying the composite hydroxide, the composite hydroxide may be coated by spraying an aqueous solution or slurry in which a compound containing the additive element M is dissolved and drying. Furthermore, coating by a method such as spray drying a slurry in which the composite hydroxide and the compound containing the additive element M are suspended, or by mixing the composite hydroxide and the compound containing the additive element M by a solid phase method. You can also

In addition, when the surface of the secondary particles of the composite hydroxide is coated with the additive element M, the raw material is It is necessary to appropriately adjust the composition of the aqueous solution and the coating aqueous solution. Moreover, the coating step may be performed on the heat-treated particles after heat-treating the composite hydroxide.

(7) Production Apparatus The crystallization apparatus (reaction tank) for producing the composite hydroxide of the present invention is particularly limited as long as it can switch the reaction atmosphere and the raw material aqueous solution. never. However, it is preferred to use a batch crystallizer in which the precipitated product is not collected until the crystallization reaction is complete. With such a crystallizer, unlike a continuous crystallizer that recovers the product by an overflow method, the growing particles are not recovered at the same time as the overflow liquid. Secondary particles can be easily obtained. In addition, in the method for producing a composite hydroxide of the present invention, it is necessary to appropriately control the reaction atmosphere during the crystallization reaction, so it is preferable to use a closed crystallizer.

3. Positive electrode active material for lithium ion secondary battery (1) Particle structure The positive electrode active material of the present invention is a ternary lithium-nickel-manganese-cobalt-containing composite oxide containing at least nickel, manganese, and cobalt as transition metals. A positive electrode active material for a lithium ion secondary battery of the present invention, comprising secondary particles formed by agglomeration of a plurality of primary particles. In the positive electrode active material of the present invention, as shown in FIG. agglomerated portions 8 made of primary particles and electrically connected to the outer shell portion 7; and space portions 9 distributed between the aggregated portions 8 inside the outer shell portion have a qualitative structure.

In particular, in the positive electrode active material of the present invention, in the secondary particles having such a porous structure, the individual primary particles constituting the outer shell portion 7 and the aggregation portion 8 indicated by symbol A in FIG. and comprising a grain structure 10a having a high nickel ratio composition in which the nickel ratio, which is the atomic ratio of nickel to the sum of nickel, manganese and cobalt, is greater than 0.4, and wherein the composition comprises The surface layer portion 10b is graded to have a low nickel ratio of more than 0.1 to 0.4 or less.

Here, "electrically conductive" means that the aggregated portions of the primary particles are structurally connected to each other and are electrically conductive. Further, the "outer shell portion" corresponds to a portion where the outermost shell layer and the third low-density layer formed on the outermost side of the secondary particles of the composite hydroxide, which is the precursor, are sintered and shrunk. In addition, the "aggregated part" corresponds to the part where the central part of the secondary particles of the composite hydroxide that is the precursor, the first low-density layer, the high-density layer, and the second low-density layer undergo sintering shrinkage. . Furthermore, in the "space", the fine primary particles that constitute the first low-density portion and the second low-density portion of the secondary particles of the composite hydroxide that is the precursor are absorbed by the surrounding plate-like primary particles. It is a pore structure formed by These spaces exist apart from each other due to the existence of the aggregated parts, but communicate with each other and the outside through the grain boundaries and voids between the primary particles, allowing the electrolyte and the conductive aid to penetrate into the spaces. is possible.

Due to such a particle structure, the positive electrode active material of the present invention achieves both a larger specific surface area and a higher tap density than conventional positive electrode active materials having a hollow structure. In the positive electrode active material having the particle structure of the present invention, the electrolyte penetrates into the interior of the secondary particles through the grain boundaries, voids, or spaces between the primary particles. Lithium can be desorbed and intercalated inside the particles as well. Moreover, in this positive electrode active material, the outer shell portion and the aggregation portion are electrically connected, and the cross-sectional area of the path is sufficiently large, so that the resistance inside the particles (internal resistance) can be greatly reduced. can.

In the positive electrode active material of the present invention, the outer shell portion forming the skeleton of the secondary particles and the primary particles forming the aggregation portion, except for the surface layer portion, have a high nickel ratio composition of more than 0.4. , By improving the nickel ratio in the overall composition of the ternary positive electrode active material, the energy density is improved, and the primary particles themselves are protected by the surface layer portion having a composition graded to a low nickel ratio, so that the electrolyte It suppresses the deterioration of the structure of the secondary particles due to the contact with.

The high nickel ratio composition has a nickel ratio in the range of greater than 0.4 to 1 or less. The nickel ratio is preferably in the range of more than 0.4 and 0.8 or less, more preferably in the range of 0.45 to 0.7. If the nickel ratio is 0.4 or less, the nickel ratio in the overall composition of the positive electrode active material cannot be made sufficiently higher than the conventional 0.33 (the ratio of nickel, manganese, and cobalt is 1:1:1). .

On the other hand, in the composition with a low nickel ratio in the surface layer portion of the primary particles, the nickel ratio is in the range of more than 0.1 to 0.4 or less. The nickel ratio is preferably in the range of more than 0.1 and 0.38 or less, more preferably in the range of 0.2 to 0.36. Typically, the nickel ratio can be 0.33 (1:1:1 nickel:manganese:cobalt ratio). If the nickel ratio of the surface layer portion exceeds 0.4, the protection of the primary particles of the aggregation portion by the surface layer portion becomes insufficient, and the effect of suppressing the deterioration of the secondary particles becomes insufficient.

When a lithium ion secondary battery is constructed by using a positive electrode active material having such a structure as a positive electrode material, the durability of the positive electrode active material is improved, and the output characteristics deteriorate due to the resistance of the positive electrode interface resistance due to its deterioration. is prevented, and the output characteristics can be further improved without impairing the battery capacity and cycle characteristics.

(2) Average particle size MV
The positive electrode active material of the present invention is adjusted to have an average particle size MV of 3 μm to 10 μm, preferably 4 μm to 9 μm, more preferably 4 μm to 8 μm. If the average particle size of the positive electrode active material is in such a range, not only can the battery capacity per unit volume of the secondary battery using this positive electrode active material be increased, but also safety and output characteristics can be improved. can do. On the other hand, if the average particle size MV is less than 3 μm, the filling property of the positive electrode active material is lowered, and the battery capacity per unit volume cannot be increased. On the other hand, if the average particle size MV exceeds 10 μm, the reaction area of the positive electrode active material is reduced, and the interface with the electrolyte is reduced, making it difficult to improve the output characteristics.

The average particle size MV of the positive electrode active material means the volume-based average particle size (Mean Volume Diameter), as in the case of the composite hydroxide described above, and was measured, for example, with a laser light diffraction/scattering particle size analyzer. It can be obtained from the integrated volume value.

(3) Particle size distribution In the positive electrode active material of the present invention, [(d90-d10)/average particle size MV], which is an index showing the spread of the particle size distribution, is 0.70 or less, preferably 0.60 or less, more preferably 0.60 or less. is 0.55 or less, and is composed of secondary particles with an extremely narrow particle size distribution. Such a positive electrode active material has a low ratio of fine particles and coarse particles, and a secondary battery using this has excellent safety, cycle characteristics, and output characteristics.

On the other hand, when [(d90-d10)/average particle size MV] exceeds 0.70, the ratio of fine particles and coarse particles in the positive electrode active material increases. For example, if the proportion of fine particles is high, the secondary battery is likely to generate heat due to the local reaction of the fine particles, which not only lowers safety, but also selectively degrades the fine particles, thereby reducing the cycle time. characteristics are inferior. Further, when the proportion of coarse particles is large, a sufficient reaction area between the electrolyte and the positive electrode active material cannot be ensured, resulting in inferior output characteristics.

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

The meanings of d10 and d90 in the index [(d90-d10)/average particle size MV] indicating the spread of the particle size distribution and the method of obtaining them are the same as in the case of the composite hydroxide described above.

(4) Primary Particles In the positive electrode active material of the present invention, the primary particles forming the outer shell portion and the aggregation portion are formed with an average particle size in the range of 0.01 μm to 0.3 μm. As in the case of composite hydroxide, the size of the primary particles is determined by embedding the secondary particles in a resin or the like, processing the cross section with a polisher or the like, and then making the cross section observable. It is obtained by observing using a SEM such as SEM, measuring the maximum outer diameter (major axis diameter) of 10 or more primary particles present in the cross section of the secondary particles, and calculating the average value. The positive electrode active material is produced by firing the composite hydroxide, which is a precursor, under appropriate firing conditions, so that the plate-like primary particles that make up the precursor absorb the fine primary particles and shrink during sintering. Primary particles having the above size are formed. If the average particle diameter of the primary particles is less than 0.01 μm, there is a possibility that a problem will arise that the batteries will become fragile and sufficient battery performance will not be obtained. On the other hand, if the average particle size of the primary particles exceeds 0.3 μm, the solid diffusion distance in the particles becomes long, which may cause a problem that sufficient battery performance cannot be obtained.

In the positive electrode active material of the present invention, the composition of each of the primary particles forming the outer shell portion and the aggregation portion is generally uniform inside the structure. However, as shown in FIG. 4, each of the primary particles denoted by symbol A basically has a grain structure 10a having a high nickel ratio composition, while the surface layer portion 10b is graded to a low nickel ratio composition. is becoming The presence and composition of the surface layer 10b can be measured by scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS or STEM-EDX).

Therefore, the surface layer portion 10b whose composition is graded from the high nickel ratio composition to the low nickel ratio composition cannot be clearly distinguished and recognized from the other portions as shown in FIG. 4, and has the high nickel ratio composition. In the primary particles of the agglomerated part, it is judged to exist when it is confirmed that a composition with a low nickel ratio exists on the surface of the primary particles by scanning transmission electron microscope-energy dispersive X-ray spectroscopy. is.

(5) Outer Shell Portion The outer shell portion constituting the secondary particles is composed of aggregates of primary particles having a composition with a low nickel ratio. The thickness of the outer shell is preferably in the range of 0.1 μm to 1.0 μm. If the thickness of the outer shell is less than 0.1 μm, the strength of the secondary particles of the positive electrode active material is not sufficiently ensured. On the other hand, if the thickness of the outer shell portion exceeds 1.0 μm, the number of primary particles having a composition with a low nickel ratio becomes too large, making it difficult to make the entire positive electrode active material have a composition with a high nickel ratio. The thickness of the outer shell is preferably in the range of 0.1 μm to 0.5 μm, more preferably in the range of 0.12 μm to 0.3 μm.

(6) The crystallite diameter obtained from the X-ray diffraction pattern of the (003) plane The positive electrode active material of the present invention is obtained by using the Scherrer formula from the half-value width of the peak of the (003) plane by X-ray diffraction. The crystallite diameter is in the range of 300 Å to 1500 Å, preferably in the range of 400 Å to 1300 Å, more preferably in the range of 700 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 300 Å, the primary particles are fine, and the pores existing between the primary particles in the positive electrode active material are too fine, resulting in Since it becomes difficult for the electrolyte to penetrate, the reaction area with the electrolyte decreases, and the output characteristics of the secondary battery deteriorate. On the other hand, when the crystallite diameter of the (003) plane exceeds 1500 Å, the primary particles become too coarse, the ratio of pores in the secondary particles is extremely reduced, and the electrolyte infiltration route is reduced. The reaction area with the electrolyte decreases, and the output characteristics of the secondary battery deteriorate.

(7) Tap density Increasing the capacity of secondary batteries is an important issue in order to extend the usage time of portable electronic devices and the driving distance of electric vehicles. On the other hand, the electrode thickness of the secondary battery is required to be about several μm from the viewpoint of the packing and electronic conductivity of the battery as a whole. For this reason, it is necessary not only to use a high-capacity positive electrode active material, but also to improve the filling property of the positive electrode active material to increase the capacity of the secondary battery as a whole.

From this point of view, the positive electrode active material of the present invention has a tap density of 1.1 g/cm ³ to 1.8 g/cm It is preferred to keep it in the range of ³ . When the tap density is less than 1.1 g/cm ³ , even if the BET specific surface area is increased, the fillability is low, and the overall battery capacity of the secondary battery may not be sufficiently improved. On the other hand, the upper limit of the tap density is not particularly limited, but in the case of the grain structure of the present invention, the upper limit under normal manufacturing conditions is about 1.8 g/cm ³ . The tap density is preferably 1.2 g/cm ³ or more, more preferably 1.4 g/cm ³ or more.

The tap density refers to the bulk density after tapping a sample powder collected in a container 100 times based on JIS Z-2504, and can be measured using a shaking specific gravity meter.

(8) BET Specific Surface Area The positive electrode active material of the present invention is characterized in that the specific surface area is improved due to the existence of the space formed inside the secondary particles. As the specific surface area of the positive electrode active material in the present invention, for example, the BET specific surface area measured by the BET method using nitrogen gas adsorption is used. In the positive electrode active material of the present invention, the BET specific surface area is preferably as large as possible as long as the structure of the secondary particles described above is maintained. This is because the larger the BET specific surface area, the larger the contact area with the electrolyte, and the output characteristics of the secondary battery using this can be greatly improved. Specifically, the BET specific surface area of the positive electrode active material of the present invention is preferably in the range of 2.0 ^{m 2} /g to 5.0 ^{m 2} /g. In the present invention, when the specific surface area of the positive electrode active material is less than 2.0 m ² /g, a sufficient reaction area with the electrolyte cannot be secured when a secondary battery is constructed, and the output characteristics are sufficiently improved. It becomes difficult to let The BET specific surface area is more preferably 2.5 m ² /g to 5.0 m ² /g, even more preferably 3.0 m ^{2 /} g to 6.0 ^{m 2} /g.

(9) Oil Absorption The positive electrode active material of the present invention is characterized in that the output characteristics are improved by having a porous structure having a space formed inside the secondary particles. In the present invention, it is possible to use the oil absorption as an index indicating the existence ratio of the voids present in the secondary particles (hereinafter referred to as "voids ratio").

The oil absorption is determined by operating according to the procedure described in "JIS K 6217-4 (Carbon black for rubber - Basic properties - Part 4: Determination of oil absorption (including compressed samples))". However, since the operation process is complicated, the oil absorption is generally measured using an oil absorption (absorption) measuring device that is commercially available in accordance with the above JIS. In addition, usually, di-n-butyl phthalate (di-n-butyl phthalate, DBP) is used as the oil (oil) for measurement, and the measurement result is calculated as the oil absorption per 100 g of the sample. Therefore, the unit is expressed as "ml/100g".

The oil absorption of the positive electrode active material of the present invention is preferably in the range of 35 ml/100 g to 60 ml/100 g, more preferably in the range of 40 ml/100 g to 55 ml/100 g. As the oil absorption increases, the proportion of the space occupied by the secondary particles constituting the positive electrode active material, that is, the proportion of the space, increases, tending to increase the specific surface area. Therefore, if the oil absorption is less than 35 ml/100 g, it can be evaluated that a sufficient space is not formed and the effect of increasing the specific surface area cannot be obtained. On the other hand, if the oil absorption exceeds 60 ml/100 g, a large number of structural voids are present inside the secondary particles, and the proportion of aggregated parts becomes too low, making it impossible to obtain desired properties.

(10) Composition _The composition of the ternary positive electrode active material of the present invention is not limited as long as it has the structure described _{above .} Co _z M _t O ₂ (−0.05≦u≦0.50, x+y+z+t=1, 0.4≦x≦0.70, 0.15≦y≦0.4, 0.15≦z≦0. 3, 0 ≤ t ≤ 0.1, M is one or more additional elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) , a positive electrode active material comprising a lithium-nickel-manganese-cobalt-containing composite oxide having a hexagonal crystal structure with a layered structure.

In this positive electrode active material, the value of u, which indicates the excess amount of lithium (Li), is preferably in the range of −0.05 to 0.50, more preferably in the range of 0 to 0.50, still more preferably 0 to 0. be in the .35 range. By limiting the value of u to the above range, the output characteristics and battery capacity of a secondary battery using this positive electrode active material as a positive electrode material 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 secondary batteries. It is preferably in the range of 0.4 to 0.7, more preferably in the range of 0.43 to 0.65, still more preferably in the range of 0.5 to 0.6. If the value of x is less than 0.4, the energy density of the secondary battery using this positive electrode active material cannot be sufficiently improved. On the other hand, when the value of x exceeds 0.7, the content of other elements decreases, and the effect as a ternary positive electrode active material cannot be obtained.

Manganese (Mn) is an element that contributes to improving thermal stability, and the value of y indicating its content is preferably in the range of 0.15 to 0.4, more preferably 0.2 to 0.35. be in the range of If the value of y is less than 0.15, the thermal stability of the secondary battery using this positive electrode active material cannot be improved. On the other hand, 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 preferably in the range of 0.15 to 0.3, more preferably 0.2 to 0.2. Keep it in the range of 25. When the value of z exceeds 0.3, the initial discharge capacity of the secondary battery using this positive electrode active material 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 (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W) can be used.

The value of t, which indicates the content of additive element M, is preferably in the range of 0 to 0.1, more preferably in the range of 0.001 to 0.05. When the value of t exceeds 0.1, the metal elements contributing to the Redox reaction decrease, resulting in a decrease in battery capacity.

Such additive element M may be dispersed 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 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.

4. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Batteries The method for producing a positive electrode active material of the present invention uses the composite hydroxide described above as a precursor, and a positive electrode having a predetermined particle structure, average particle size MV and particle size distribution. There are no particular restrictions as long as the active material can be synthesized. However, assuming industrial-scale production, the above-described composite hydroxide is mixed with a lithium compound to obtain a lithium mixture. It is preferable to synthesize the positive electrode active material by a manufacturing method including a sintering step of sintering at 920°C. In addition, if necessary, steps such as a heat treatment step and a calcining step may be added to the above-described steps. According to such a manufacturing method, it is possible to easily obtain the positive electrode active material described above, particularly the positive electrode active material represented by the general formula (B).

(1) Heat Treatment Step In the method for producing a positive electrode active material of the present invention, a heat treatment step may optionally be provided before the mixing step so that the composite hydroxide is made into heat treated particles and then mixed with the lithium compound. Here, the heat-treated particles include not only composite hydroxides from which excess moisture has been removed in the heat treatment step, but also nickel-manganese-cobalt-containing composite oxides (hereinafter referred to as “composite oxides”) converted to oxides in the heat treatment step. ), or mixtures thereof.

The heat treatment step is a step of removing excess moisture contained in the composite hydroxide by heating the composite hydroxide to 105° C. to 750° C. 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, and to suppress variation in the composition of the obtained positive electrode active material.

The heating temperature in the heat treatment step is set to 105.degree. C. to 750.degree. If the heating temperature is less than 105° C., excess moisture in the composite hydroxide cannot be removed, and variations may not be sufficiently suppressed. On the other hand, even if the heating temperature exceeds 700° C., no further effect can be expected, and the production cost increases.

In the heat treatment step, the number of atoms of each metal component in the positive electrode active material and the number of atoms of Li may be removed to the extent that there is no variation in the number of atoms. It doesn't have to be converted into something. 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 hydroxides are converted to composite oxides by heating to 400° C. or higher. is preferred. In addition, by determining the metal components contained in the composite hydroxide according to the heat treatment conditions in advance by analysis and determining the mixing ratio with the lithium compound, the above-described variation 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, it is preferably at least 1 hour, more preferably 5 to 15 hours.

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

In the mixing step, the ratio of the sum (Me) of the number of metal atoms other than lithium in the lithium mixture, specifically nickel, cobalt, manganese and the additive element M, to the number of lithium atoms (Li) ( Li/Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, more preferably 1.0 to 1.2, It is necessary to mix the composite hydroxide 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 or heat-treated particles and the lithium compound are mixed so that Li/Me in the mixing process becomes Li/Me of the desired positive electrode active material. It is necessary to

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 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 800°C, preferably 450°C to 780°C, may be performed. Thereby, lithium can be sufficiently diffused in the composite hydroxide or the heat-treated particles, and a more uniform lithium composite oxide 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 The firing step is a step of firing the lithium mixture obtained in the mixing step under predetermined conditions to diffuse lithium into the composite hydroxide or heat-treated particles to obtain a lithium composite oxide. .

In this sintering step, the plate-like primary particles that make up the central portion, high-density layer, and high-density portion of the composite hydroxide and the heat-treated particles absorb the fine primary particles while sintering, shrinking, and after sintering The primary particles form the outer shell portion and aggregate portion of the positive electrode active material. The fine primary particles start to sinter from a lower temperature range than the plate-like primary particles, and shrink more than the plate-like primary particles. It is absorbed by the central portion, the high-density layer, and the outer shell layer, where the progress of knotting is slow, and a moderately sized space is formed as a pore. At this time, the plate-like primary particles contract while maintaining their connection with the adjacent plate-like primary particles, so in the resulting positive electrode active material, the electrical connection between the outer shell portion and the aggregation portion is Conduction can be achieved and a sufficient cross-sectional area of the path can be ensured. As a result, the internal resistance of the positive electrode active material is greatly reduced, and when a secondary battery is constructed, it becomes possible to improve the output characteristics without impairing the battery capacity and cycle characteristics.

The particle structure of such a positive electrode active material is basically determined according to the particle structure of the precursor composite hydroxide, but it may be affected by its composition and firing conditions. It is preferable to adjust each condition appropriately so as to obtain a desired structure after performing a preliminary test.

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.

a) Firing temperature The firing temperature of the lithium mixture must be 650°C to 920°C. If the firing temperature is less than 650° C., lithium does not sufficiently diffuse into the composite hydroxide or the heat-treated particles, and excess lithium or unreacted composite hydroxide or heat-treated particles remain, or the obtained positive electrode active material is deteriorated. Crystallinity may be insufficient. On the other hand, if the firing temperature exceeds 920° C., the pores in the secondary particles of the positive electrode active material may be crushed, and the secondary particles of the positive electrode active material are violently sintered, resulting in abnormal grain growth. This results in an increase in the proportion of irregularly shaped coarse particles. From the viewpoint of controlling the size of the agglomeration part and the space part that constitute the secondary particles within a range of appropriate sizes, the firing temperature of the lithium mixture is preferably 700 ° C. to 920 ° C., and 800 ° C. to 900 ° C. is more preferable.

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 or the heat-treated particles and the lithium compound can be reacted more uniformly.

b) Firing Time Of the firing time, the retention time at the firing temperature described above is preferably at least 2 hours, more preferably 4 to 24 hours. If the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the composite hydroxide or the heat-treated particles, and excess lithium or unreacted composite hydroxide or heat-treated particles remain, or the obtained positive electrode The crystallinity of the active material 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 3 ° C./min to 7 ° C./min. By controlling the cooling rate within such a range, it is possible to secure productivity and prevent equipment such as a sagger from being damaged by rapid cooling.

c) 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. is particularly 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 positive electrode active material may be insufficient.

(5) Pulverization step The secondary particles forming the positive electrode active material 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. Thereby, the average particle size and particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range. In addition, crushing refers to applying mechanical energy to aggregates composed of multiple secondary particles generated by sintering necking between secondary particles during firing, and almost without 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 to an appropriate range so as not to destroy the secondary particles.

5. Lithium Ion Secondary Battery The lithium ion secondary battery of the present invention can have the same configuration as a general nonaqueous electrolyte secondary battery, which includes components such as a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. . Alternatively, the lithium-ion secondary battery of the present invention can have a configuration similar to that of a general solid electrolyte secondary battery, including constituent members such as a positive electrode, a negative electrode, and a solid electrolyte. That is, the present invention is widely applicable from non-aqueous electrolyte secondary batteries to all-solid lithium secondary batteries, as long as the secondary batteries charge and discharge by desorption and insertion of lithium ions. The embodiments described below are merely examples, and the present invention is applied to lithium ion secondary batteries in which various modifications and improvements are made based on the embodiments described herein. It is possible.

(1) Components a) Positive Electrode Using the positive electrode active material described above, for example, a positive electrode of a lithium ion secondary battery is produced as follows.

First, a positive electrode active material of the present invention is mixed with a conductive material and a binder, and if necessary, activated carbon and a solvent for adjusting viscosity are added and 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. The content of the conductive material can be 1 to 20 parts by mass, and the content of the binder can be 1 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. 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 is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin or polyacryl. Acids can be used.

In addition, 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 Metallic lithium, lithium alloys, or the like can be used for the negative electrode. In addition, a binder is mixed with a negative electrode active material capable of intercalating and deintercalating lithium ions, and an appropriate solvent is added to form a paste. , dried and optionally formed by compression to increase electrode density.

Examples of negative electrode active materials include materials containing lithium such as metallic 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, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. Solvents can be used.

c) Separator The separator is sandwiched between the positive electrode and the negative electrode in the non-aqueous electrolyte secondary battery, and has the function of separating the positive electrode and the negative electrode and retaining the non-aqueous 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) Electrolyte As the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery, a non-aqueous electrolytic solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent is used.

Organic solvents used in the non-aqueous electrolyte 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; , ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, and the like, or two or more of them. can be mixed and used.

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.

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

On the other hand, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ and Li ₂ S—SiS ₂ are used as solid electrolytes for solid electrolyte secondary batteries such as all-solid lithium secondary batteries. be able to. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

Inorganic solid electrolytes include oxide solid electrolytes, sulfide solid electrolytes, and the like.

As the oxide solid electrolyte, an oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. For example, lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO ₄ , Li ₄ SiO ₄ - Li ₃ VO ₄ , Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ —ZnO, Li _1+X Al _X Ti _2-X (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _2/3-X TiO ₃ (0≦ _{X ≦ 2 / 3 ) , Li5La3Ta2O12 , Li7La3Zr2O12 , Li6BaLa2Ta2O12 , Li3.6Si0.6P0.4O4 , etc.} can be used.

As the sulfide solid electrolyte, a sulfide containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. For example, Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI—Li ₂ S—B ₂ S ₃ , Li _{3PO4 - Li2S} - _Si2S , Li3PO4 _{- Li2S - SiS2 , LiPO4 - Li2S} -SiS, LiI- _Li2SP2O5 , LiI _{- Li3PO4} -P ₂ S ₅ and the like can be used.

Examples of inorganic solid electrolytes other than oxide solid electrolytes and sulfide solid electrolytes include Li ₃ N, LiI, and Li ₃ N--LiI--LiOH.

A polymer compound exhibiting ion conductivity can be used as the organic solid electrolyte. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. In addition, the organic solid electrolyte can contain a supporting salt (lithium salt).

When a solid electrolyte is used, the solid electrolyte can be mixed in the positive electrode material to ensure contact between the electrolyte and the positive electrode active material.

(2) Configuration of lithium ion secondary battery The configuration of the lithium ion secondary battery is not particularly limited. A configuration consisting of a positive electrode, a negative electrode, a solid electrolyte, and the like in the next battery can be adopted. Moreover, the shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be adopted.

In the case of a non-aqueous electrolyte secondary battery, for example, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode current collector and the positive electrode leading to the outside are used. A terminal and a negative electrode current collector and a 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 a lithium ion secondary battery.

(3) Characteristics of lithium ion secondary battery As described above, the lithium ion secondary battery of the present invention has a porous structure having a composition with a high nickel ratio of the present invention and uses a ternary positive electrode active material as a positive electrode material. Excellent capacity, output and cycle characteristics. Moreover, in the positive electrode active material of the present invention, the primary particles constituting the outer shell portion and the aggregation portion as a whole have a composition with a high nickel ratio, but the surface layer portion whose composition is graded to a low nickel ratio has a high nickel ratio. Since it has a structure that protects the primary particles themselves having a composition with a nickel ratio, in comparison with a conventional lithium ion secondary battery using a positive electrode active material with a porous structure having a uniform composition with a high nickel ratio, the same While maintaining a high energy density, the positive electrode interfacial resistance can be reduced, and the discharge capacity retention rate can be further improved.

(4) Use of lithium ion secondary battery The lithium ion secondary battery of the present invention, as described above, has excellent capacity characteristics, output characteristics, and cycle characteristics, and these characteristics are required at a high level. It can be suitably used as a power source for portable electronic devices (laptop personal computers, smart phones, tablet terminals, digital cameras, etc.). In addition, the lithium ion secondary battery of the present invention not only enables miniaturization and high output, but also has excellent safety and durability, and can simplify expensive protection circuits. It can also be suitably used as a power source for transportation equipment such as electric vehicles that are limited in space.

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 composite hydroxides and positive electrode active materials unless otherwise specified. In addition, throughout the nucleation step and particle growth step, the pH value of the reaction aqueous solution was measured by a pH controller (Nisshin Rika Co., Ltd., NPH-690D), and based on this measured value, the supply amount of the sodium hydroxide aqueous solution was adjusted. By adjusting, the fluctuation width of the pH value of the reaction aqueous solution in each step was controlled within the range of ±0.2.

(Example 1)
a) Production of composite hydroxide [Nucleation step]
First, 14 L of water was put into the reaction vessel and the temperature inside the vessel was set to 40° C. while stirring. At this time, nitrogen gas was passed through the reaction tank for 30 minutes to make the reaction atmosphere a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. Subsequently, appropriate amounts of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water are supplied into the reaction tank so that the pH value is 12.6 at a liquid temperature of 25° C. and the ammonium ion concentration is 10 g/L. to form a pre-reaction aqueous solution.

At the same time, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in water so that the molar ratio of the respective metal elements was Ni:Mn:Co=5:3:2, and a 2 mol/L first raw material aqueous solution was prepared. was prepared. Further, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in water so that the molar ratio of the respective metal elements was Ni:Mn:Co=1:1:1, and a 2 mol/L second raw material aqueous solution was prepared. was prepared.

Next, the first raw material aqueous solution was supplied to the pre-reaction aqueous solution at 115 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 value and the ammonium ion concentration of the aqueous solution for nucleation within the ranges described above.

[Particle growth step]
After the nucleation was completed, the supply of all the aqueous solution was temporarily stopped, and sulfuric acid was added to adjust the pH value to 11.2 based on the liquid temperature of 25° C., thereby forming an aqueous solution for particle growth. . After confirming that the pH value has reached a predetermined value, the first raw material aqueous solution is supplied at a constant rate of 115 ml/min, which is the same as in the nucleation step, to remove the nuclei (particles) generated in the nucleation step. grown up.

As a first step, after the crystallization in the non-oxidizing atmosphere is continued for 35 minutes (13.0% of the entire grain growth process) from the start of the grain growth process, the supply of the first raw material aqueous solution is stopped. Then, at the same time as starting to supply the second raw material aqueous solution, air is circulated in the reaction vessel using a ceramic air diffuser (manufactured by Kinoshita Rika Kogyo Co., Ltd.) having a pore size of 20 μm to 30 μm to create a reaction atmosphere. , the oxygen concentration was adjusted to an oxidizing atmosphere of 21% by volume (switching operation 1).

As a second step, after continuing crystallization in an oxidizing atmosphere using the second raw material aqueous solution from the switching operation 1 for 20 minutes (7.4% with respect to the entire grain growth process), the second raw material aqueous solution and restarting the supply of the first raw material aqueous solution, and at the same time, nitrogen is circulated in the reaction vessel using an air diffuser, and the reaction atmosphere is changed to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. adjusted (switching operation 2).

As a third step, after continuing crystallization in a non-oxidizing atmosphere using the first raw material aqueous solution from switching operation 2 for 65 minutes (24.1% of the entire grain growth process), the first raw material The supply of the aqueous solution was stopped, and the supply of the second raw material aqueous solution was restarted. 3).

As a fourth stage, after the crystallization reaction in the oxidizing atmosphere using the second raw material aqueous solution from the switching operation 3 is continued for 40 minutes (14.8% with respect to the entire grain growth process), the second raw material The supply of the aqueous solution is stopped and the supply of the first raw material aqueous solution is restarted, and at the same time, nitrogen is circulated in the reaction vessel using an air diffuser, and the reaction atmosphere is a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. (switching operation 4).

As a fifth step, after continuing crystallization in a non-oxidizing atmosphere using the first raw material aqueous solution from switching operation 4 for 70 minutes (25.9% of the entire grain growth process), the first raw material The supply of the aqueous solution was stopped, and the supply of the second raw material aqueous solution was restarted. 5).

As the sixth step, after the crystallization reaction in the oxidizing atmosphere using the second raw material aqueous solution from the switching operation 5 is continued for 40 minutes (14.8% with respect to the entire grain growth process), the second raw material The particle growth process was terminated by stopping the supply of all aqueous solutions containing the aqueous solutions. After that, the obtained product was washed with water, filtered and dried to obtain a powdery composite hydroxide. The percentage of crystallization reaction in the entire oxidizing atmosphere was 37.0%.

In the grain growth process, 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 value and the ammonium ion concentration of the aqueous solution for particle growth within the ranges described above. .

b) Evaluation of composite hydroxide [Composition]
According to analysis using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPE-9000), the composition of this composite hydroxide has the general formula: Ni _0.43 Mn _0.32 Co _0.25 (OH) ₂ It was confirmed that it is represented by

[Particle structure]
Part of the composite hydroxide is embedded in a resin, cross section polisher (manufactured by JEOL Ltd., IB-19530CP) is processed to make the cross section observable, and 10 or more secondary particles of the composite hydroxide. was observed with a field emission scanning electron microscope (FE-SEM: JSM-6360LA manufactured by JEOL Ltd.). As a result, this composite hydroxide has a central portion formed by agglomeration of plate-like primary particles, and a first low-density layer formed by agglomeration of fine primary particles on the outside of the central portion. , a high-density layer formed by agglomeration of plate-like primary particles, a second low-density layer formed by agglomeration of fine primary particles, and an outer shell layer formed by agglomeration of plate-like primary particles , and a third low-density layer formed by agglomeration of fine primary particles, and part of the plate-shaped primary particles constituting the central part, the high-density layer, and the outer shell layer are interconnected It was confirmed that

Regarding the ratio of the radius of the central part, the thickness of the first low density layer, the high density layer, the second low density layer, the outer shell layer, and the third low density layer to the particle size of the secondary particles It was measured and calculated to be 20%, 10%, 5%, 5%, 5% and 5% respectively.

[Average particle size MV and particle size distribution]
Using a laser light diffraction scattering particle size analyzer (Microtrac MT3300EXII manufactured by Microtrac Bell Co., Ltd.), the average particle diameter MV of the secondary particles of the composite hydroxide is measured, and d10 and d90 are measured, [(d90-d10)/average particle size MV], which is an index showing the spread of the particle size distribution, was calculated. As a result, it was confirmed that the average particle size MV was 5.5 μm and [(d90−d10)/average particle size MV] was 0.50.

c) Preparation of positive electrode active material After heat-treating the composite hydroxide obtained as described above at 120 ° C. for 12 hours in an air stream (oxygen concentration: 21% by volume) (heat treatment step), Li / Me 1.10, it was sufficiently mixed with lithium hydroxide 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 800° C. at a temperature elevation rate of 1.5° C./min in an oxygen (oxygen concentration: 100% by volume) stream, and sintered by holding at this temperature for 3 hours. It was cooled to room temperature at about 4°C/min (firing step). 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 and particle size distribution (pulverization step).

d) Evaluation of positive electrode active material [Composition]
According to analysis using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPE-9000), the composition of this positive electrode active material has the general formula: Li _1.10 Ni _0.43 Mn _0.32 Co _0.25 O ₂ was confirmed.

[Particle structure]
Part of the positive electrode active material is embedded in a resin, cross-section polisher (manufactured by JEOL Ltd., IB-19530CP) is processed so that the cross section can be observed, and then SEM (FE-SEM: manufactured by JEOL Ltd., JSM -6360LA). As a result, the positive electrode active material is composed of secondary particles formed by aggregation of a plurality of primary particles, and the secondary particles are dispersed in the outer shell and inside the outer shell, It was confirmed that it has an aggregated portion electrically connected to the outer shell portion, and a space portion having a pore structure in which primary particles do not exist and which exists between the aggregated portions inside the outer shell portion. . In addition, the average thickness of the outer shell portion of the secondary particles was 0.3 μm from the observation of the cross-sectional image containing arbitrary 10 or more secondary particles obtained from the SEM observation.

[Crystallite diameter]
Using an X-ray diffraction (XRD) device (X'Pert PRO manufactured by Spectris Co., Ltd.), powder X-ray diffraction analysis using CuKα rays was performed, and each diffraction peak was analyzed except for the broadening of the diffraction peaks in the X-ray diffraction pattern. When the crystallite diameter of the (003) plane was calculated using Scherrer's formula from the above, it was 550 Å.

[Composition of Outer Shell Part and Aggregate Part]
Scanning transmission electron microscope-Energy dispersive X-ray spectroscopy (STEM-EDS) device (HD-2300A, manufactured by Hitachi High-Technologies Co., Ltd.) was used. It was confirmed that the ratios of nickel, manganese and cobalt were all 5:3:2.

[Surface layer of primary particles]
Using a scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS) device (manufactured by Hitachi High-Technologies Corporation, HD-2300A), the nickel concentration in the surface layer of the primary particles of the aggregated portion was measured. It was 37 atomic %. In addition, after making a cross-sectional observable state by cross-section polisher (manufactured by JEOL Ltd., IB-19530CP), a scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS) device (Hitachi High Technologies) HD-2300A manufactured by Co., Ltd.) was used to measure the thickness of the surface layer, and the thickness of the surface layer was less than 0.01 μm.

[Average particle size MV and particle size distribution]
Using a laser light diffraction scattering particle size analyzer (Microtrac MT3300EXII manufactured by Microtrac Bell Co., Ltd.), the average particle size MV of the positive electrode active material is measured, and d10 and d90 are measured to determine the spread of the particle size distribution. [(d90-d10)/average particle diameter MV], which is an index showing the particle diameter, was calculated. As a result, it was confirmed that the average particle diameter MV was 5.4 μm and [(d90−d10)/average particle diameter MV] was 0.42.

[BET specific surface area and tap density]
The BET specific surface area was measured using a flow-type gas adsorption specific surface area measuring device (manufactured by Mountec Co., Ltd., Macsorb 1200 series), and the tap density was measured using a tapping machine (manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd., KRS-406). As a result, it was confirmed that the BET specific surface area was 4.2 m ² /g and the tap density was 1.38 g/cm ³ .

[Oil absorption]
JIS K 6217-4 (Carbon black for rubber - Basic properties - Part 4: Determination of oil absorption (including compressed sample))" oil absorption measurement device (manufactured by Asahi Research Institute Co., Ltd., S-500) The oil absorption was measured using di-n-butyl phthalate (di-n-butyl phthalate, DBP) as the oil (oil) for measurement. As a result, it was confirmed that the oil absorption was 51.0 ml/100 g.

e) Production of Secondary Battery A 2032-type coin battery 11 as shown in FIG. 5 was produced. Specifically, the positive electrode active material obtained as described above: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg are mixed and pressed at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. After molding, the positive electrode 12 was produced by drying at 120° C. for 12 hours in a vacuum dryer.

Next, using this positive electrode 12, a 2032 type coin battery was produced in an Ar atmosphere glove box with a controlled dew point of -80°C. Lithium metal with a diameter of 17 mm and a thickness of 1 mm was used for the negative electrode 13 of this 2032-type coin battery, and ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as the supporting electrolyte were used as the non-aqueous 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 14 . In this manner, a 2032-type coin battery 11 having a gasket 15 and including a positive electrode can 16 and a negative electrode can 17 was assembled.

f) Battery evaluation [Positive electrode interfacial resistance]
The positive electrode interface resistance was measured using an impedance measurement method, charging a 2032 type coin battery at a charging potential of 4.4 V, and using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B). The Nyquist plot shown was obtained. The Nyquist plot shown in FIG. 6 is represented as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance (interfacial resistance) and its capacity. A fitting calculation was performed using the equivalent circuit shown to calculate the value of the positive electrode interfacial resistance. As for the positive electrode interfacial resistance, the positive electrode active material of Comparative Example 1 described later is used as a reference, and the resistance reduction rate with respect to this is shown. As a result, the positive electrode interfacial resistance was reduced to 0.765 times that of Comparative Example 1.

[Discharge capacity retention rate]
The 2032 type coin battery was left for about 24 hours after it was produced, and after the open circuit voltage (OCV) 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. , and after resting for 1 hour, a charge/discharge test was performed to measure the discharge capacity when the cutoff voltage reached 3.0 V, and the initial discharge capacity was obtained. Furthermore, charging and discharging were repeated 100 times, and the ratio of the second discharge capacity to the initial discharge capacity was defined as the discharge capacity retention rate. As a result, the discharge capacity retention rate was 92%.

Table 1 shows the composition and characteristics of the outer shell portion, the aggregation portion, and the whole of the obtained positive electrode active material, and the characteristics of the obtained lithium ion secondary battery. These are also shown in Table 1 for Example 2 and Comparative Example 1.

(Example 2)
Nickel sulfate, manganese sulfate, and cobalt sulfate are dissolved in water so that the molar ratio of the respective metal elements is Ni:Mn:Co=6:3:1 to prepare a 2 mol/L first raw material aqueous solution. A composite hydroxide, a positive electrode active material, and a lithium ion secondary battery were obtained in the same manner as in Example 1, except for the above.

The composition of the composite hydroxide was the general formula: Ni _0.5 Mn _0.3 Co _0.2 (OH) ₂ . In addition, the radius of the central portion, the first low-density layer, the high-density layer, the second low-density layer, the outer shell layer, and the third low-density layer with respect to the particle size of the secondary particles of the composite hydroxide The layer thickness ratios were 25%, 8%, 4%, 4%, 5% and 4%, respectively. Furthermore, the average particle diameter MV was 5.5 μm, and [(d90−d10)/average particle diameter MV] was 0.50.

_{The composition} of the positive electrode active material was _the general _formula : _{Li1.10Ni0.5Mn0.3Co0.2O2} . The average thickness of the outer shell portion of the secondary particles was 0.3 μm, and the crystallite diameter of the (003) plane was 560 Å. The ratio of nickel, manganese and cobalt in the outer shell portion and aggregate portion of the secondary particles was 6:3:1. The nickel concentration in the surface layer portion of the primary particles of the agglomerated portion was 37 atomic %, and the thickness thereof was less than 0.01 μm. The average particle size MV was 5.4 μm, and [(d90−d10)/average particle size MV] was 0.42. Furthermore, the BET specific surface area was 4.2 m ² /g, the tap density was 1.32 g/cm ³ and the oil absorption was 53.0 ml/100 g.

In the lithium ion secondary battery using this positive electrode active material, the positive electrode interfacial resistance was reduced to 0.828 times that of Comparative Example 1. The discharge capacity retention rate was 88%.

(Comparative example 1)
Nickel sulfate, manganese sulfate, and cobalt sulfate were mixed into the first aqueous raw material solution and the second aqueous raw material solution, and the molar ratio of the respective metal elements was Ni:Mn:Co=5:3:2. to prepare only a 2 mol/L raw material aqueous solution, and without switching the raw material aqueous solution in the switching operation 4, the crystallization reaction in the fifth stage is continued, and the process is switched to the sixth stage. A composite hydroxide, a positive electrode active material, and a lithium-ion secondary battery were obtained in the same manner as in Example 1, except that the crystallization reaction was terminated in the fifth step.

The composition of the composite hydroxide was the general formula: Ni _0.5 Mn _0.3 Co _0.2 (OH) ₂ . In addition, the ratio of the radius of the central portion, the thickness of the first low-density layer, the high-density layer, the second low-density layer, and the outer shell layer to the particle size of the secondary particles of the composite hydroxide is , 25%, 10%, 5%, 5%, and 5%, respectively. Furthermore, the average particle diameter MV was 5.5 μm, and [(d90−d10)/average particle diameter MV] was 0.50.

_{The composition} of the positive electrode active material was _the general _formula : _{Li1.10Ni0.5Mn0.3Co0.2O2} . The average thickness of the outer shell portion of the secondary particles was 0.3 μm, and the crystallite diameter of the (003) plane was 530 Å. The ratios of nickel, manganese, and cobalt in the outer shell portion and aggregate portion of the secondary particles were all 5:3:2. The average particle size MV was 5.2 μm, and [(d90−d10)/average particle size MV] was 0.42. Furthermore, the BET specific surface area was 4.2 m ² /g, the tap density was 1.4 g/cm ³ and the oil absorption was 50.0 ml/100 g.

The discharge capacity retention rate of the lithium ion secondary battery using this positive electrode active material was 80%.

In the lithium ion secondary batteries using the positive electrode active materials of Examples 1 and 2, which are within the scope of the present invention, in comparison with Comparative Example 1, the positive electrode interfacial resistance decreased, and the discharge capacity retention rate was confirmed to be improving.

REFERENCE SIGNS LIST 1 central portion 2 first low-density layer 3 high-density layer 4 second low-density layer 5 outer shell layer 6 third low-density layer 7 outer shell portion 8 aggregation portion 9 space portion 10a primary particles 10b surface layer of primary particles Part 11 Coin Battery 12 Positive Electrode (Evaluation Electrode)
13 Negative electrode 14 Separator 15 Gasket 16 Positive electrode can 17 Negative electrode can

Claims (20)

A nickel-manganese-cobalt precursor of a positive electrode active material for a lithium-ion secondary battery, comprising secondary particles formed by aggregation of a plurality of plate-like primary particles and fine primary particles smaller than the plate-like primary particles. containing complex hydroxide,
The secondary particles are composed of a central portion formed mainly by agglomeration of the plate-like primary particles, a first low-density layer formed mainly by agglomeration of the fine primary particles outside the central portion, and Outside the first low-density layer, a high-density layer formed mainly by aggregating the plate-like primary particles, and outside the high-density layer, a second layer formed mainly by aggregating the fine primary particles A low-density layer, an outer shell layer formed mainly by aggregation of the plate-like primary particles outside the second low-density layer, and an outer shell layer mainly formed by aggregation of the fine primary particles a third low density layer formed by
The core, the high density layer, and the outer shell layer have a high nickel ratio composition in which the nickel ratio, which is the atomic ratio of nickel to the sum of nickel, manganese, and cobalt, is greater than 0.4; The first low-density layer, the second low-density layer, and the third low-density layer have a low nickel ratio composition in which the nickel ratio is more than 0.1 and not more than 0.4.
Composite hydroxide containing nickel manganese cobalt. The average particle diameter MV of the secondary particles is in the range of 4 μm to 11 μm, and [(d90−d10)/average particle diameter MV], which is an index showing the spread of the particle size distribution of the secondary particles, is 0. The nickel-manganese-cobalt-containing composite hydroxide according to claim 1, wherein the nickel-manganese-cobalt-containing composite hydroxide is .65 or less. The radius of the central portion is in the range of 20% to 40% of the particle size of the secondary particles, and the thickness of the first low density layer is 3% to 15% of the particle size of the secondary particles. range, the thickness of the high-density layer is in the range of 2% to 10% of the particle size of the secondary particles, and the thickness of the second low-density layer is in the range of the particle size of the secondary particles. In the range of 2% to 10%, the thickness of the outer shell layer is in the range of 2% to 10% of the particle size of the secondary particles, and the thickness of the third low-density layer is in the range of the second 3. The nickel-manganese-cobalt-containing composite hydroxide according to claim 1, wherein the particle size of the secondary particles is in the range of 2% to 10%. General formula (A): _NixMnyCozMt ( _OH ) _{2 +a} (x+y+z+ _t =1, 0.4≤x≤0.70, 0.15≤y≤0.4, 0.15≤z≤0 .3, 0≤t≤0.1, 0≤a≤0.5, M is selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W1 4. The nickel-manganese-cobalt-containing composite hydroxide according to any one of claims 1 to 3, having a composition represented by additional elements above seeds). A raw material aqueous solution containing at least a transition metal and an aqueous solution containing an ammonium ion donor are supplied into a reaction tank to form a reaction aqueous solution, and a nickel-manganese-cobalt-containing composite hydroxide is obtained by a crystallization reaction. A method for producing a nickel-manganese-cobalt-containing composite hydroxide, comprising
In the step of obtaining the nickel-manganese-cobalt-containing composite hydroxide, the concentration of ammonium ions in the reaction aqueous solution is controlled to be in the range of 3 g/L to 25 g/L,
In the step of obtaining the nickel-manganese-cobalt-containing composite hydroxide, the pH value of the reaction aqueous solution at a liquid temperature of 25 ° C. is controlled to be in the range of 12.0 to 14.0, thereby generating nuclei. The pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step and the nucleus generation step is lower than the pH value in the nucleation step and is in the range of 10.5 to 12.0 at a liquid temperature of 25 ° C. A particle growth step for growing the nuclei by controlling to be
(1) adjusting the reaction atmosphere in the first stage of the nucleation step and the grain growth step to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less; (2) after the first stage of the grain growth step, (3) changing the reaction atmosphere from the non-oxidizing atmosphere to an oxidizing atmosphere having an oxygen concentration of more than 5% by volume as the second stage of the grain growth process; (4) next, the reaction atmosphere is switched from the non-oxidizing atmosphere to the oxidizing atmosphere to perform the particle growth; (5) switching the reaction atmosphere from the oxidizing atmosphere to the non-oxidizing atmosphere as a fifth step of the grain growth process; (6) finally, the reaction atmosphere is switched from the non-oxidizing atmosphere to the oxidizing atmosphere to continue the crystallization reaction as the sixth step of the grain growth process , and
The raw material aqueous solution supplied in the first, third, and fifth stages of the nucleation step and the grain growth step has a nickel ratio of 0, which is the atomic ratio of nickel to the total of nickel, manganese, and cobalt. The aqueous feedstock solution having a composition with a high nickel ratio greater than .4 and supplied in stages 2, 4, and 6 of the grain growth process has a nickel ratio greater than 0.1 to 0. .have a composition with a low nickel fraction that is no greater than 4;
A method for producing a nickel-manganese-cobalt-containing composite hydroxide. The switching of the reaction atmosphere is defined as the ratio of the amount of metal added in each stage to the total amount of metal added in the grain growth process, and the crystallization reaction in each stage for the entire grain growth process. Regarding the ratio, the first stage is in the range of 8% to 20%, the second stage is in the range of 2% to 20%, the third stage is in the range of 12% to 40%, and the fourth stage is in the range of 3% to 40%. %, 10% to 40% in the fifth stage, and 2% to 20% in the sixth stage, the method for producing a nickel-manganese-cobalt-containing composite hydroxide according to claim 5. The _nickel -manganese- _cobalt -containing composite hydroxide has the general formula (A): _NixMnyCozMt ( _OH ) _2+a (x+y+z+t=1, 0.4≤x≤0.70, 0.15≤y≤ 0.4, 0.15≦z≦0.3, 0≦t≦0.1, 0≦a≦0.5, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo , Hf, Ta, and one or more additional elements selected from W). A positive electrode active material for a lithium-ion secondary battery comprising a lithium-nickel-manganese-cobalt-containing composite oxide,
The positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles, and the secondary particles are composed of an outer shell formed by the agglomerated primary particles and an inner side of the outer shell. a cohesive portion that is formed by the agglomerated primary particles and is electrically connected to the outer shell portion, and a space that exists dispersedly in the cohesive portion; and
Each of the primary particles constituting the outer shell portion and the aggregation portion has a high nickel ratio composition in which the nickel ratio, which is the atomic ratio of nickel to the total of nickel, manganese, and cobalt, exceeds 0.4, And, the composition has a surface layer portion graded to a low nickel ratio composition in which the nickel ratio is more than 0.1 and 0.4 or less,
Positive electrode active material for lithium ion secondary batteries. 9. The positive electrode active material for a lithium ion secondary battery according to claim 8, wherein the thickness of the outer shell portion of said secondary particles is in the range of 0.1 μm to 1.0 μm. The average particle diameter MV of the secondary particles is in the range of 3 μm to 10 μm, and [(d90−d10)/average particle diameter MV], which is an index showing the spread of the particle size distribution of the secondary particles, is 0. 10. The positive electrode active material for a lithium ion secondary battery according to claim 8 or 9, which is .7 or less. The positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 10, wherein said positive electrode active material has a tap density in the range of 1.1 g/cm ³ to 1.8 g/cm ³ . 12. The positive electrode active material for a lithium ion secondary battery according to claim 8, wherein said positive electrode active material has a BET specific surface area in the range of 2.0 m ² /g to 5.0 m ² /g. 13. The positive electrode active material for a lithium ion secondary battery according to claim 8, wherein said positive electrode active material has an oil absorption in the range of 35 ml/100 g to 60 ml/100 g. The crystallite diameter of the primary particles obtained by using the Scherrer formula from the half-value width of the peak of the (003) plane in X-ray diffraction of the (003) plane of the positive electrode active material is in the range of 300 Å to 1500 Å. 14. The positive electrode active material for lithium ion secondary batteries according to any one of 8 to 13. The lithium nickel manganese _cobalt containing composite _{oxide has a} general formula (B _{) :} ≤0.70, 0.15≤y≤0.4, 0.15≤z≤0.3, 0≤t≤0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, one or more additive elements selected from W), having a hexagonal crystal structure having a layered structure, the lithium ion according to any one of claims 8 to 14. Positive electrode active material for secondary batteries. A mixing step of mixing a nickel-manganese-cobalt-containing composite hydroxide and a lithium compound to form a lithium mixture, and oxidizing the lithium mixture formed in the mixing step with an oxygen concentration of 18% by volume to 100% by volume. a firing step of obtaining a positive electrode active material for a lithium-ion secondary battery comprising a lithium-nickel-manganese-cobalt-containing composite oxide by firing at a temperature in the range of 650°C to 920°C in a sexual atmosphere;
Using the nickel-manganese-cobalt-containing composite hydroxide according to any one of claims 1 to 4 as the nickel-manganese-cobalt-containing composite hydroxide,
A method for producing a positive electrode active material for a lithium ion secondary battery. In the mixing step, the lithium mixture is adjusted so that the ratio of the sum of the number of metal atoms other than lithium contained in the lithium mixture to the number of lithium atoms is 1:0.95 to 1.5. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 16. The lithium ion secondary battery according to claim 16 or 17, further comprising a heat treatment step of heat-treating the nickel-manganese-cobalt-containing composite hydroxide at a temperature in the range of 105°C to 750°C before the mixing step. A method for producing a positive electrode active material for The cathode active material for a lithium ion secondary battery has a general formula (B): Li _1+u Ni _{x Mny} Co _{z MtO 2} (−0.05≦u≦0.50, x+y+z+t=1, 0.4≦ x≦0.70, 0.15≦y≦0.4, 0.15≦z≦0.3, 0≦t≦0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta, and W), and is composed of a lithium-nickel-manganese -cobalt- containing composite oxide having a hexagonal crystal structure with a layered structure . 19. A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of 16 to 18. A positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, or a positive electrode, a negative electrode, and a solid electrolyte, and as a positive electrode active material used for the positive electrode, for the lithium ion secondary battery according to any one of claims 8 to 15. A lithium ion secondary battery using a positive electrode active material.

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