JP7272140B2 - Positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for lithium ion secondary batteries, more specifically, a positive electrode active material for lithium ion secondary batteries comprising a compound-coated lithium-nickel-containing composite oxide containing W and Li, a method for producing the same, and and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery as a positive electrode material.

In recent years, with the spread of mobile electronic devices such as smartphones, tablet terminals, digital cameras, and laptop computers, there is a strong demand for the development of small, lightweight non-aqueous electrolyte secondary batteries with high energy density. In addition, there is a strong demand for the development of high-capacity, 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 ) has 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.

As for the lithium-transition metal-containing composite oxide, emphasis is placed on the development of high output by reducing its internal resistance. From this point of view, lithium-nickel-cobalt-aluminum-containing composite oxides (NCA), which have improved properties of lithium-nickel composite oxides, are also attracting attention. Lithium-nickel-manganese-cobalt-containing composite oxides have superior weather resistance and are easier to handle than lithium-nickel-cobalt-aluminum-containing composite oxides. is considered the most important in

As described above, ternary positive electrode active materials composed of lithium-nickel-manganese-cobalt-containing composite oxides are required to have a high level of output power by further reducing internal resistance, especially in power supply applications for electric vehicles. It is

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 a non-aqueous electrolyte can be secured. Since the movement distance between the positive electrode and the negative electrode 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 output characteristics, it is considered effective to control the shape of the positive electrode active material and form a space in the positive electrode active material into which the non-aqueous electrolyte can enter. By adopting such a structure, the positive electrode resistance can be greatly reduced because the reaction area with the non-aqueous electrolyte can be increased compared to a positive electrode active material with a solid structure having the same particle size. 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, Japanese Patent Application Laid-Open No. 2018-104273 describes a crystallization reaction in which the pH value of the reaction aqueous solution is adjusted to a range of 12.0 to 14.0 to generate nuclei, and the generated nuclei are The pH value of the reaction aqueous solution containing the The atmosphere is controlled to be non-oxidizing in the initial stage of the grain growth process, and at a predetermined timing in the grain growth process, the atmosphere is switched to the oxidizing atmosphere and then switched to the non-oxidizing atmosphere again at least twice. A method for producing a transition metal-containing composite hydroxide is disclosed.

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 or more 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.

On the other hand, a method of adding a tungsten compound to a lithium-transition metal-containing composite oxide is being studied in order to increase the output of a lithium-ion battery by further reducing the internal resistance.

For example, in JP-A-2015-216105, a lithium mixture obtained by mixing a nickel compound and a lithium compound is fired in an oxidizing atmosphere at a temperature range of 700 ° C. to 780 ° C. for 1 hour to 6 hours, and has the general formula: Li _b Ni _1-x-y Co _x My _{O 2} (wherein M represents at least one element selected from Mg, Al, Ca, Ti, V, Cr, Mn, Nb, Zr and Mo; .95 ≤ b ≤ 1.03, 0 < x ≤ 0.15, 0 < y ≤ 0.07, x + y ≤ 0.16), and is composed of primary particles and secondary particles in which the primary particles are agglomerated. A contained composite oxide is obtained as a base material, a tungsten compound is added during or after the water washing treatment of the base material, W is dispersed on the surface of the primary particles of the base material, and the W is dispersed in an oxygen atmosphere or a vacuum atmosphere. A cathode active material for a lithium ion secondary battery has been proposed, which is obtained by heat treatment at a temperature of 100° C. to 600° C. and has fine particles of a compound containing W and Li on the surfaces of primary particles of a base material.

Further, in JP-A-2017-084513, a tungsten compound is added during or after water-washing treatment of a base material obtained in the same manner as in JP-A-2015-216105 to reduce the moisture content of the base material to 6.0%. W is dispersed on the surface of the primary particles of the base material in a state controlled to 5% by mass to 11.5% by mass, and is obtained by heat treatment at a temperature of 100°C to 600°C in an oxygen atmosphere or a vacuum atmosphere. , a positive electrode active material for a lithium ion secondary battery has been proposed, which has a coating containing W and Li on the surface of the primary particles of the base material and having a thickness of 1 nm to 200 nm.

By allowing fine particles and/or coating of a compound containing W and Li, such as lithium tungstate, to exist on the surface of the primary particles constituting the lithium-transition metal-containing composite oxide of the base material, these fine particles or coating form lithium It functions as a protective film that prevents contact between the transition metal-containing composite oxide and the electrolyte and suppresses the formation of deposits such as phosphate. Therefore, it is considered that the interfacial resistance can be reduced.

It is important that the fine particles and/or coating of the compound containing W and Li such as lithium tungstate exist uniformly on the surface of the primary particles constituting the lithium-transition metal-containing composite oxide of the base material. In addition, it is important that fine particles and/or films of compounds containing W and Li, such as lithium tungstate, are uniformly formed between lithium-transition metal-containing composite oxides.

From this point of view, in JP-A-2018-186065, a lithium transition metal-containing composite oxide as a base material and tungsten oxide are mixed, and water is sprayed and mixed to obtain a lithium mixture, By drying the lithium mixture, the amount of tungsten present on the surface, including secondary particles composed of a plurality of primary particles aggregated and lithium tungstate, is 0.1 mass with respect to the whole % or more and 1.0% by mass or less, and the amount of tungsten present therein is 0.1% by mass or more and 1.0% by mass or less with respect to the whole. It is proposed to obtain the substance. By such a method, in the presence of water, the neutralization reaction between excess lithium such as liberated lithium hydroxide and tungsten oxide can proceed more uniformly on the surface of the lithium-transition metal-containing composite oxide as the base material. supposed to be possible.

JP 2018-104273 A JP 2015-216105 A JP 2017-084513 A JP 2018-186065 A

In order to further increase the output of a positive electrode active material comprising a lithium-nickel-manganese-cobalt-containing composite oxide having a porous structure, the present inventors have developed a lithium-nickel-manganese-cobalt-containing composite oxide having a porous structure as a base material, By dry-mixing with a tungsten compound, further spraying water to obtain a mixture, and drying the mixture, a positive electrode comprising a compound-containing lithium-nickel-manganese-cobalt-containing composite oxide containing W and Li A study was conducted on obtaining an active material.

As a result, in the positive electrode active material having a structure in which fine particles and/or a film of a compound containing W and Li such as lithium tungstate are formed on the surface of the secondary particles, the coating uniformity of the compound containing W and Li is improved. It was found that it is possible to make improvements.

The present invention further increases the power output of the compound-coated lithium-nickel-manganese-cobalt-containing composite oxide containing W and Li having a porous structure by allowing the coating of the compound containing W and Li, such as lithium tungstate, to exist more uniformly. The purpose is to

The present invention contains at least nickel, manganese, and cobalt as transition metals, and consists of secondary particles having a porous structure, and fine particles of a compound containing W and Li, such as lithium tungstate, on at least the surfaces of the secondary particles. A cathode active material for a ternary lithium-ion secondary battery comprising a compound-coated lithium-nickel-manganese-cobalt-containing composite oxide (NMC) containing W and Li having a porous structure, and/or a coating comprising a film, and its The present invention relates to a manufacturing method and a lithium ion secondary battery using the positive electrode active material for lithium ion secondary batteries as a positive electrode material.

A positive electrode active material for a lithium ion secondary battery according to a first aspect of the present invention is a ternary positive electrode active material made of a lithium-nickel-manganese-cobalt-containing composite oxide, and is formed by aggregation of a plurality of primary particles. A compound-coated lithium-nickel-manganese-cobalt-containing composite containing W and Li, wherein a coating consisting of fine particles and/or a coating of a compound containing W and Li is present on at least the surfaces of the secondary particles. The present invention relates to a positive electrode active material for lithium ion secondary batteries made of oxide.

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, the positive electrode active material for lithium ion secondary batteries of the present invention is based on the XPS spectrum obtained by the surface analysis of the secondary particles by X-ray photoelectron spectroscopy, W and Li present on the surface of the secondary particles The coverage of the compound containing is in the range of 5% to 80%.

The size of the fine particles is preferably in the range of 5 nm to 400 nm. Also, the thickness of the coating is preferably in the range of 1 nm to 200 nm.

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. 0.70 or less is preferred.

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 tap density of the positive electrode active material is preferably in the range of 1.0 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 for a non-aqueous electrolyte secondary battery of the present invention has the general formula (A): Li _1+u Ni _{x Mny} Co _{z Ws} M _t O ₂ (−0.05≦u≦0.50, x+y+z+s+t=1 , 0.3≦x≦0.7, 0.15≦y≦0.4, 0.15≦z≦0.4, 0.001≦s≦0.03, 0≦t≦0.1, M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), and has a hexagonal layered rock salt crystal structure It is preferably composed of a lithium-nickel-manganese-cobalt-containing composite oxide.

A method for producing a positive electrode active material for a lithium ion secondary battery according to a second aspect of the present invention comprises:
It is composed of secondary particles formed by aggregating a plurality of primary particles, and the secondary particles are present inside the outer shell formed by the agglomerated primary particles and the outer shell, and the agglomerated It has a porous structure that is formed of primary particles and has an aggregated portion that is electrically connected to the outer shell portion, and a space that exists dispersedly in the aggregated portion. , a lithium-nickel-manganese-cobalt-containing composite oxide, which is a base material, is mixed with a tungsten compound in an amount in the range of more than 0.4% by mass and 5% by mass or less with respect to the total mass of the composite oxide. , a dry mixing step for obtaining a mixture (first mixing step),
The mixture contains a lithium compound in an amount such that the molar ratio of Li to W in the tungsten compound is 1.2 or more, and an amount of water in the range of 2% to 30% by mass relative to the total mass of the mixture. A lithium compound aqueous solution spray mixing step (second mixing step) for further mixing the mixture by spraying the lithium compound aqueous solution, and
The mixture is heat treated at a temperature of 500° C. or less to dry the mixture, and a compound-coated lithium-nickel-manganese-cobalt-containing composite containing W and Li, wherein a coating of the compound containing W and Li exists on the surface of the primary particles. a drying step to obtain an oxide;
characterized by comprising

The mixed amount of the tungsten compound is preferably 0.7% by mass or more with respect to the total mass of the composite oxide.

The tungsten compound is preferably tungsten oxide.

The average particle size d50 of the tungsten compound is preferably in the range of 0.1 μm to 70 μm.

In the lithium compound aqueous solution, the lithium compound is preferably contained in such an amount that the molar ratio of Li to W in the tungsten compound is in the range of 1.2-10.

In the lithium compound aqueous solution, the water is preferably contained in an amount ranging from 5% by mass to 25% by mass with respect to the total mass of the mixture.

The lithium compound is preferably lithium hydroxide.

The dry mixing step is preferably carried out for a time in the range of 5 to 60 minutes while stirring at a peripheral speed in the range of 5 m/s to 10 m/s.

In the lithium compound aqueous solution spray mixing step, while stirring at a peripheral speed in the range of 5 m / sec to 10 m / sec, the lithium compound aqueous solution is sprayed at a spray speed in the range of 50 ml / min to 100 ml / min, and then It is preferable to continue mixing for a time ranging from 5 minutes to 60 minutes while stirring at a peripheral speed ranging from 5 m/s to 10 m/s.

After the lithium compound aqueous solution spray mixing step and before the drying step, the mixture is heated at a temperature in the range of 50 ° C. to 80 ° C. for 1.5 hours to 2 hours. It is preferable to include a step of standing still for a period of time.

After the lithium compound aqueous solution spray mixing step or the standing step and before the drying step, the mixture is stirred at a peripheral speed in the range of 5 m / sec to 10 m / sec for 5 minutes to 5 minutes. Preferably, an additional mixing step (third mixing step) is provided, mixing for a time in the range of 60 minutes.

The _positive electrode _active material for _a lithium ion secondary battery has a general formula (A ₎ : Li1 _{+ uNixMnyCozWsMtO2} (-0.05≤u≤0.50, x+y+z+s+t=1 _, 0. 3≤x≤0.7, 0.15≤y≤0.4, 0.15≤z≤0.4, 0.001≤s≤0.03, 0≤t≤0.1, M is Mg , Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), and lithium nickel manganese having a crystal structure of a hexagonal layered rock salt structure Composite oxides are preferred.

A lithium ion secondary battery according to a third 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.

According to the present invention, fine particles and/or a coating of a compound containing W and Li are formed on the surfaces of the secondary particles constituting the lithium-nickel-manganese-cobalt-containing composite oxide having a porous structure, which is the base material, without the presence of tungsten oxide. Provided is a positive electrode active material for a lithium ion secondary battery comprising a compound oxide containing lithium nickel manganese cobalt containing compound coated with W and Li in which a coating consisting of uniformly exists.

The positive electrode active material of the present invention has excellent battery characteristics due to its ternary composition as compared with conventional porous lithium-nickel-manganese-cobalt-containing composite oxides. Since the coating of the compound containing W and Li is formed uniformly without remaining tungsten, it is possible to further reduce the resistance, and it is possible to provide a lithium ion secondary battery with higher output. .

Therefore, by applying the positive electrode active material for a lithium ion secondary battery of the present invention to a positive electrode material for a lithium ion secondary battery for power supply of an electric vehicle, the durability is more excellent than in the past, and Since it becomes possible to provide high output characteristics, its industrial significance is great.

FIG. 1 is a chart showing an example of the process for producing the positive electrode active material for lithium ion secondary batteries of the present invention. FIG. 2 is a cross-sectional view schematically showing the structure of one example of a compound-coated lithium-nickel-manganese-cobalt-containing composite oxide containing W and Li, which is a positive electrode active material for lithium ion secondary batteries of the present invention. FIG. 3 is a SEM photograph of the surface of the secondary particles constituting the positive electrode active material for lithium ion secondary batteries of Example 1 of the present invention. 4 is an SEM photograph of the surface of the secondary particles of the positive electrode active material for a lithium ion secondary battery of Comparative Example 1. 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 invention will be described in the order of a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery.

1. Positive electrode active material for lithium ion secondary battery A first aspect of the present invention is a positive electrode active material for a lithium ion secondary battery (hereinafter referred to as "positive electrode active material"), that is, composed of secondary particles having a porous structure. A compound-coated lithium-nickel-manganese-cobalt-containing composite oxide (hereinafter referred to as , referred to as “composite oxide”).

(1) Particle Structure The positive electrode active material of the present invention is a ternary system containing at least nickel, manganese, and cobalt as transition metals. This positive electrode active material is composed of secondary particles formed by aggregation of a plurality of primary particles. In the positive electrode active material of the present invention, as shown in FIG. The porous body is composed of primary particles and is electrically connected to the outer shell portion 1, and has a space portion 3 dispersed between the aggregated portions 2 inside the outer shell portion 1. have a qualitative structure.

Here, "electrically conductive" means that the aggregated portions of the primary particles are structurally connected to each other and are electrically conductive. The spaces constituting the pore structure are separated from each other due to the presence of the aggregated parts, but communicate with each other and the outside through the grain boundaries and voids between the primary particles, and the non-aqueous electrolyte and the space enter the spaces. Penetration of the conductive aid 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 non-aqueous 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 secondary 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) is greatly reduced. .

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

(2) Coating composed of fine particles and/or coating of a compound containing W and Li In the positive electrode active material of the present invention, as shown in FIG. At least on the surface there is a coating consisting of fine particles 4 and/or a coating 5 of compounds containing W and Li.

In particular, in the positive electrode active material for lithium ion secondary batteries of the present invention, the fine particles 4 and/or coating 5 of the compound containing W and Li are uniformly present on at least the surfaces of the secondary particles. That is, based on the XPS spectrum obtained by the surface analysis of the secondary particles by X-ray photoelectron spectroscopy, the coverage of the compound containing W and Li present on the surface of the secondary particles is in the range of 5% to 80%. It is in.

In general, when the surface of the positive electrode active material is completely covered with a heterogeneous compound, the movement (intercalation) of lithium ions is greatly restricted. The advantage of capacity is lost.

On the other hand, fine particles and/or coatings of compounds containing W and Li have high lithium ion conductivity and have the effect of promoting movement of lithium ions. For this reason, by allowing fine particles and/or coatings of a compound containing W and Li to be present on at least the surface of the secondary particles, a conduction path of Li is formed at the interface with the electrolyte, so that the reaction of the positive electrode active material It is possible to reduce the resistance (also referred to as “positive electrode resistance”) and improve the output characteristics.

In order to make full use of the effect of the formation of fine particles and/or coating of the compound containing W and Li, the fine particles and/or coating of the compound containing W and Li should be uniformly formed on at least the surfaces of the secondary particles. is preferably formed. However, according to the studies of the present inventors, in the conventional positive electrode active material made of a compound-coated composite oxide containing W and Li, the coating made of fine particles and/or a film of a compound containing W and Li has a low coverage rate. It remained at less than about 1%, and it was found that a uniform coating was not formed.

On the other hand, the present inventors have found that tungsten, which is a material for forming fine particles and/or films of compounds containing W and Li, in order to form a more uniform coating in the manufacturing process of the positive electrode active material. Consideration was given to increasing the amount of compound. However, even if the amount of the tungsten compound is simply increased, for example, if the amount of the tungsten compound mixed exceeds 0.4% by mass with respect to the total mass of the composite oxide that is the base material, especially 0.7% by mass Even in the above cases, the effect of reducing the resistance of the secondary battery due to the formation of fine particles and / or coating of the compound containing W and Li is not sufficiently obtained, and the resistance tends to increase as the amount of the tungsten compound increases. found to be in

The present inventors have found that the reason for this is that the reaction between the lithium compound present on the surface of the base material composite oxide and the added tungsten compound is insufficient. , Even if the mixed amount of the tungsten compound exceeds 0.4% by mass with respect to the total mass of the composite oxide that is the base material, by sufficiently reacting the lithium compound and the tungsten compound, This makes it possible to uniformly form a coating composed of fine particles and/or a film of a compound containing W and Li on at least the surface of the secondary particles constituting the composite oxide that is the base material.

That is, in the present invention, a coating composed of fine particles and/or a coating of a compound containing W and Li is uniformly present on at least the surface of the secondary particles of the composite oxide, and is determined by X-ray photoelectron spectroscopy (XPS). The coverage of the compound containing W and Li present on the surface of the secondary particles is in the range of 5% to 80%, based on the XPS spectrum obtained by the surface analysis of the secondary particles.

X-ray photoelectron spectroscopy is a technique for analyzing the composition and chemical bonding state of the elements that make up the sample surface by irradiating the sample surface with X-rays and measuring the kinetic energy of photoelectrons emitted from the sample surface. . Characteristic X-rays such as Al-Kα rays and Mg-Kα rays are generally used as photoelectron excitation sources. Specifically, the coverage in the present invention is determined by measuring the XPS spectrum of 10 or more secondary particles by X-ray photoelectron spectroscopy, and from the peak intensity of the obtained XPS spectrum, the surface of the secondary particles. Among the constituent elements, the ratio (W / (W + Ni + Mn + Co)) of the amount of W to the amount of other elements (at least Ni, Mn, Co, and W) other than lithium is obtained, and the average is calculated. obtained by

Note that W present on the surface of the secondary particles is lithium tungstate (Li ₂ WO ₄ ) or lithium tungstate hydrate (7Li ₂ WO _{4.4H 2} O) instead of tungsten oxide (WO ₃ ). Something can be confirmed from the results of monochromatic powder XRD analysis using an X-ray diffraction (XRD) instrument.

By using a positive electrode active material having such properties as a positive electrode material, in a secondary battery, the positive electrode resistance is reduced, thereby reducing the voltage lost in the secondary battery and actually applying it to the load side. High output is obtained because the applied voltage is relatively high. In addition, since the lithium is sufficiently inserted and removed from the positive electrode by increasing the voltage applied to the load side, the battery capacity is also improved. Furthermore, the reduction in positive electrode resistance reduces the load on the positive electrode active material during charging and discharging, and thus the cycle characteristics can be improved.

Since contact with the electrolytic solution occurs on the surfaces of the primary particles, in the present invention, the surfaces of the primary particles constituting the surfaces of the secondary particles are coated with fine particles and/or films of compounds containing W and Li. It is important to be That is, in the present invention, the surface of the primary particles mainly means the surface of the primary particles exposed on the outer surface of the secondary particles. However, as shown in FIG. 2, not only the surface of the secondary particles, but also the surface of the primary particles exposed to the space 3 on the inner surface of the outer shell 1 constituting the secondary particles, The surface of the primary particles exposed in the space 3 of is also included in the surface of the primary particles. Furthermore, even grain boundaries between primary particles are included in the surface of the primary particles if the bonding of the primary particles is incomplete and the electrolyte can permeate.

Thus, in the present invention, it is sufficient that the fine particles and/or coating of the compound containing W and Li are formed on at least the surface of the secondary particles, but the outer shell portion 1 and the It can be formed on the surface exposed to the space 3 of the primary particles forming the aggregation portion 2 . Furthermore, it can also be formed on a portion of the surface of other primary particles that can come into contact with the electrolytic solution.

The higher the presence ratio of the fine particles and/or the film of the compound containing W and Li on the surface of the primary particles exposed on the outer surface of the secondary particles constituting the positive electrode active material, the more the effect of reducing the reaction resistance is obtained. Cheap. From this point of view, fine particles of a compound containing W and Li present on the surface of the secondary particles and / or based on the XPS spectrum obtained by surface analysis of the secondary particles by X-ray photoelectron spectroscopy The coverage with the film is preferably 40% or more, more preferably 50% or more.

When the compound containing W and Li exists in the form of fine particles, the particle size of the fine particles of the compound containing W and Li is preferably in the range of 5 nm to 400 nm. If the particle diameter is less than 5 nm, the fine particles may not have sufficient lithium ion conductivity. On the other hand, if the particle diameter exceeds 400 nm, the coating formed by the fine particles becomes non-uniform, and the effect of reducing the reaction resistance may not be sufficiently obtained.

The particle size of the fine particles of the compound containing W and Li is preferably in the range of 10 nm to 350 nm, more preferably in the range of 20 nm to 300 nm. It is preferable that 50% or more of the total number of fine particles formed on the surface of the primary particles have a particle diameter in the range of 10 nm to 350 nm. In this case, a higher effect of improving battery characteristics can be obtained.

For the same reason, the average particle diameter of the fine particles of the compound containing W and Li is preferably in the range of 30 nm to 100 nm, more preferably in the range of 40 nm to 80 nm. By regulating the average particle diameter in this way, the fine particles of the compound containing W and Li are made finer than the conventional compound-coated positive electrode active material containing W and Li, and the surface of the secondary particles is more uniform and uniform. It becomes possible to make it exist more evenly.

The coating of the compound containing W and Li preferably has a thickness in the range of 1 nm to 200 nm. If the thickness is less than 1 nm, the coating may not have sufficient lithium ion conductivity. On the other hand, when the thickness exceeds 200 nm, the reaction area is reduced and the bulk resistance of the electrode is increased, and the effect of reducing the reaction resistance may not be sufficiently obtained. The size of the fine particles of the compound containing W and Li or the thickness of the coating can be 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. , observed using a scanning transmission electron microscope (STEM), the size (maximum diameter) of fine particles present in the cross section of 10 or more secondary particles, or the thickness of the coating (at least the minimum and maximum thickness ) is obtained by measuring

If fine particles and/or coatings of a compound containing W and Li exist non-uniformly between the particles constituting the composite oxide, lithium ions move non-uniformly between the particles. load is applied to it, and this tends to lead to deterioration of cycle characteristics and an increase in reaction resistance. Therefore, it is preferable that fine particles and/or coatings of the compound containing W and Li are uniformly present even between the particles constituting the composite oxide.

In addition, it is not prevented that the fine particles of the compound containing W and Li are mixed with the film to cover at least the surface of the secondary particles. In the manufacturing process of the positive electrode active material, one or both of the fine particles of the compound containing W and Li and/or the coating is formed depending on the conditions for forming the coating composed of the fine particles of the compound containing W and Li and/or the coating. may occur.

This condition is basically determined by the moisture content of the powder before drying after being spray-mixed with the lithium compound aqueous solution, which will be described later. When the moisture content of the powder at that time is 3.0% by mass or more and less than 6.5% by mass, fine particles of a compound containing W and Li are preferentially formed. However, even in this case, a thin film with a thickness of about 2 nm may be formed. When the moisture content of the powder is 6.5% by mass or more, a film of the compound containing W and LI tends to be formed, and the film and fine particles are mixed. By setting the moisture content of the powder to 9.0% by mass or more, a film of a compound containing W and Li can be preferentially formed.

The moisture content of the powder before drying after being spray-mixed with the lithium compound aqueous solution is calculated from the mass of the powder after being spray-mixed with the lithium compound aqueous solution and before drying, and the mass of the powder after drying it at 180°C for 3 hours. Moisture content = (mass of powder after spray-mixing aqueous solution of lithium compound and before drying-mass of powder after drying)/(mass of powder before drying after spray-mixing aqueous solution of lithium compound)”.

The properties of the secondary particles, including the thickness of the coating of the fine particles of the compound containing W and Li, are, for example, cross-sectional observation with a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM), scanning It can be determined by cross-sectional elemental mapping by EDX analysis of a transmission electron microscope (STEM), cross-sectional observation by a transmission electron microscope, or the like. By these means, in the positive electrode active material of the present invention, it can be confirmed that the surfaces of the primary particles constituting the composite oxide are uniformly coated with a compound containing W and Li. .

In the present invention, the compound containing W and Li that constitutes the fine particles and/or the film of the compound containing W and Li is preferably lithium tungstate. _{Lithium tungstate is Li2WO4 , Li4WO5 , Li6WO6 , Li2W4O13 , Li2W2O7 , Li6W2O9 , Li2W2O7 , Li2 _} It is preferably in the _{form of at} least one selected _{from W5O16, Li9W19O55 , Li3W10O30 , Li18W5O15 ,} and _{hydrates thereof} . By forming such lithium tungstate, the lithium ion conductivity is further increased, and the effect of reducing the reaction resistance is further increased.

The identification of compounds containing W and Li can be obtained from the results of qualitative analysis using powder X-ray diffraction (XRD).

The number of atoms of W contained in the compound containing W and Li is relative to the total number of atoms of metals other than Li, i.e., Ni, Mn, Co, and additive element M, contained in the particles constituting the positive electrode active material. , preferably 0.1 atomic % to 3.0 atomic %, more preferably 0.1 atomic % to 1.0 atomic %, and 0.1 atomic % to 0.1 atomic %. It is more preferable to be in the range of 6 atomic %. This makes it possible to achieve both high charge/discharge capacity and output characteristics.

If the W content is less than 0.1 atomic %, the effect of improving the output characteristics may not be sufficiently obtained. When the amount of W exceeds 3.0 atomic %, the coating amount of the fine particles of the compound containing W and Li and/or the film becomes too thick, the BET specific surface area of the positive electrode active material decreases, and the bulk resistance of the electrode increases. Therefore, a sufficient reaction resistance reduction effect may not be obtained.

Also, the amount of Li contained in the coating of the compound containing W and Li is not particularly limited, and the effect of improving the lithium ion conductivity can be obtained as long as Li is contained. However, the amount of Li is preferably sufficient to form lithium tungstate.

(3) Composition The positive electrode active material of the present invention is composed of a lithium-nickel-manganese-cobalt-containing composite oxide having a ternary composition containing at least nickel, manganese, and cobalt, and the compound containing W and Li described above. As long as the coating consisting of fine particles and/or coating has a structure present at least on the surface of the secondary particles, the composition is not limited.

However, when the amount of W in the coating of the compound containing W and Li is in the range of 0.1 atomic % to 3.0 atomic %, the positive electrode active material of the present invention has the general formula (A): Li _1+u Ni _x Mn _y Co _z W _s M _t O ₂ (−0.05≦u≦0.50, x+y+z+s+t=1, 0.3≦x≦0.7, 0.15≦y≦0.4, 0.15≦z ≤ 0.4, 0.001 ≤ s ≤ 0.03, 0 ≤ t ≤ 0.1, M is from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W (one or more selected additive elements) and is preferably composed of a composite oxide having a crystal structure of a hexagonal layered rock salt structure. Note that W can also be contained inside the composite oxide as the additional element M, but in this case, the amount of W (s in the composition formula) does not include the amount of W contained as the additional element M. can't

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, and still more preferably in the range of 0 to 0.35. make it 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 0.3 to 0.7, more preferably in the range of 0.4 to 0.65, still more preferably in the range of 0.5 to 0.6. If the value of x is less than 0.3, the energy density of the secondary battery 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 0.4, more preferably 0.2 to 0.2. Keep it in the range of 35. When the value of z exceeds 0.4, the initial discharge capacity of the secondary battery is significantly reduced.

In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material of the present invention may contain an additive element M in addition to the metal elements described above. Such additive elements M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum At least one selected from (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. If the value of t exceeds 0.1, the amount of metal elements that contribute to the Redox reaction decreases, resulting in a decrease in battery capacity of the secondary battery.

Such an additional element M may be dispersed inside the particles of the composite oxide, or may coat the surface of the particles of the composite oxide. 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.

Identification and quantification of the composition of the positive electrode active material, including the number of W atoms contained in the compound containing W and Li, can be obtained by analysis by ICP emission spectrometry.

(4) Average particle size MV
The positive electrode active material of the present invention is adjusted so that the average particle size MV is in the range of 3 μm to 10 μm, preferably in the range of 4 μm to 9 μm, more preferably in the range of 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 diameter 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 non-aqueous 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 (MeanVolume Diameter), which can be obtained, for example, from the volume integrated value measured with a laser beam diffraction/scattering particle size analyzer.

(5) 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 non-aqueous 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.

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.

(6) 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 0.02 μm to 0.3 μm. The size of the primary particles is determined by embedding the secondary particles in a resin or the like, making the cross section observable by processing such as a cross section polisher, and then observing the cross section using an SEM such as FE-SEM. It is obtained by measuring the maximum outer diameters (major axis diameters) of 10 or more primary particles present in the cross section of the secondary particles and calculating the average value. If the average particle size of the primary particles is less than 0.02 μm, the problem may arise that the particles become fragile and sufficient battery performance cannot 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, individual primary particles have a substantially uniform composition.

(7) Outer Shell Portion The outer shell portion constituting the secondary particles is composed of agglomerates of primary particles. 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 is not sufficiently ensured. On the other hand, when the thickness of the outer shell portion exceeds 1.0 μm, there arise problems such that a space portion and aggregation portion of appropriate size are not formed inside, and the non-aqueous electrolyte does not sufficiently permeate the interior of the secondary particles. sell. 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. The thickness of the outer shell can also be obtained by measuring the thickness of the outer shell of 10 or more secondary particles by cross-sectional observation with an SEM such as FE-SEM.

(8) 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 ternary composition containing at least nickel, manganese, and cobalt, and has a porous structure. The tap density, which is an index of the sphericity of secondary particles that make up the substance, is preferably 1.0 g/cm ³ or more, and is in the range of 1.1 g/cm ³ to 1.8 g/cm ³ is more preferred. When the tap density is less than 1.0 g/cm ³ , even if the BET specific surface area is increased, the fillability may be 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 composition and 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.

(9) 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 non-aqueous 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. If the specific surface area of the positive electrode active material is less than 2.0 m ² /g, a sufficient reaction area with the non-aqueous electrolyte cannot be ensured when a secondary battery is constructed using this positive electrode active material as a positive electrode material. It becomes difficult to sufficiently improve the output characteristics. The BET specific surface area is more preferably in the range of 2.5 m ² /g to 5.0 ^{m 2} /g, even more preferably in the range of 3.0 m ^{2 /} g to 6.0 m ² /g.

2. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Batteries A second aspect of the present invention is a positive electrode active material for lithium ion secondary batteries, that is, fine particles and/or coatings of a compound containing W and Li are secondary particles. The present invention relates to a method for producing a compound-coated lithium-nickel-manganese-cobalt-containing composite oxide containing W and Li present at least on the surface.

In the method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention, a ternary composite oxide having a porous structure having the structure described above, except for the presence of a coating of a compound containing W and Li, is used as a matrix. used as material. That is, it is composed of secondary particles formed by aggregating a plurality of primary particles, and the secondary particles are present in the outer shell formed by the agglomerated primary particles and inside the outer shell, It has a porous structure comprising agglomerated portions formed by the agglomerated primary particles and electrically connected to the outer shell portion, and space portions dispersedly present in the agglomerated portions. A ternary composite oxide is used as the base material.

In the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention, a composite oxide having such a structure as a base material contains more than 0.4% by mass of the total mass of the composite oxide. , a dry mixing step (first mixing step) of mixing a tungsten compound in an amount in the range of 5% by mass or less to obtain a mixture;
The mixture contains a lithium compound in an amount such that the molar ratio of Li to W in the tungsten compound is 1.2 or more, and an amount of water in the range of 2% to 30% by mass relative to the total mass of the mixture. A lithium compound aqueous solution spray mixing step (second mixing step) for further mixing the mixture by spraying the lithium compound aqueous solution, and
The mixture is heat-treated at a temperature of 500° C. or less to dry the mixture, and a compound-coated lithium-nickel-manganese-cobalt-containing composite containing W and Li, wherein fine particles of the compound containing W and Li are present on the surface of the primary particles. a drying step to obtain an oxide;
characterized by comprising

(1) First mixing step (dry mixing step)
The first mixing step is a step of dry-mixing the composite oxide and the tungsten compound to disperse the tungsten compound on the surfaces of the primary particles constituting the secondary particles of the composite oxide. First, by dry mixing these powders, the tungsten compound can be more uniformly dispersed in the composite oxide.

The amount of the tungsten compound added is preferably in the range of more than 0.4% by mass and 5% by mass or less with respect to the total mass of the composite oxide. As a result, the amount of W dispersed on the surface of the composite oxide is 0 with respect to the total number of atoms of the metals other than lithium, that is, Ni, Mn, Co, and the additional element M contained in the composite oxide. .1 atomic % to 3.0 atomic %, and it is possible to uniformly form a coating of a compound containing W and Li on at least the surface of the secondary particles constituting the composite oxide that is the base material. becomes.

That is, when the amount of the tungsten compound added is less than 0.4% by mass with respect to the total mass of the composite oxide, the amount of the compound containing W and Li coated in the finally obtained positive electrode active material is insufficient, A coating composed of fine particles and/or a film of a compound containing W and Li is not uniformly formed, and a region having insufficient lithium ion conductivity is generated on a part of the surface of the secondary particles constituting the positive electrode active material. In some cases, it may not be possible to sufficiently obtain high output due to the effect of reducing the reaction resistance. If it exceeds 5% by mass, the amount of coating of the compound containing W and Li in the finally obtained positive electrode active material becomes too large, the BET specific surface area of the positive electrode active material decreases, and the bulk resistance of the electrode increases. , a sufficient reaction resistance reduction effect may not be obtained.

The addition amount of the tungsten compound is preferably 0.7% by mass or more, more preferably 1.1% by mass or more, relative to the total mass of the composite oxide.

The amount of W dispersed on the surface of the composite oxide is in the range of 0.1 atomic % to 3.0 atomic % with respect to the total number of atoms of Ni, Mn, Co, and M contained in the fired powder. more preferably in the range of 0.1 atomic % to 1.0 atomic %, and even more preferably in the range of 0.1 atomic % to 0.6 atomic %. By adding a tungsten compound in this range, it is possible to more uniformly form a coating of a compound containing W and Li on at least the surface of the secondary particles of the positive electrode active material, and conduct Li at the interface with the electrolyte. By forming a path, it becomes possible to further reduce the reaction resistance of the positive electrode active material.

W may be added in the form of an alkaline solution in which a tungsten compound is dissolved (hereinafter referred to as "alkaline solution (W)") or in the form of a tungsten compound.

When added as an alkaline solution (W), the tungsten compound should be soluble in the alkaline solution, and tungsten compounds that are readily soluble in alkali, such as tungsten oxide, lithium tungstate, and ammonium tungstate, should be used. is preferred.

As the alkali used for the alkaline solution (W), in order to obtain a high charge/discharge capacity, a general alkaline solution that does not contain impurities harmful to the positive electrode active material, such as ammonia or lithium hydroxide, can be used. In order to make it possible to supply a sufficient amount of Li from the excess Li and the alkaline solution (W) to form a compound containing W and Li, and from the viewpoint of not inhibiting the intercalation of Li, water Preference is given to using lithium oxide.

On the other hand, when it is added in the form of a tungsten compound, it is preferable to use an alkali-soluble tungsten compound such as tungsten oxide (WO ₃ ) as the tungsten compound. Also, tungsten compounds containing lithium, such as lithium tungstate, can be used. At least one selected from Li ₂ WO ₄ , Li ₄ WO ₅ and Li ₆ W ₂ O ₉ can be used as lithium tungstate.

When tungsten compounds such as tungsten oxide and lithium tungstate are added as they are, the average particle size d50 of these tungsten compounds is preferably 70 μm or less, specifically in the range of 0.1 μm to 70 μm. It is more preferably in the range of 0.3 μm to 50 μm. When using a tungsten compound having an average particle size d50 of more than 70 μm, or even when using tungsten oxide having an average particle size d50 of about 40 μm, which is mainly used as a conventional tungsten compound, water such as pure water is used. When the mixture of the composite oxide and the tungsten compound is subjected to the drying step immediately after the water spray mixing step used, lithium hydroxide in which the tungsten compound added is sufficiently present on the surface of the composite oxide. It cannot sufficiently react with a lithium compound such as, and unreacted tungsten compounds tend to remain.

While regulating the average particle diameter d50 of the tungsten compound to be 70 μm or less, specifically in the range of 0.1 μm to 70 μm, the lithium compound aqueous solution spray mixing step described later is performed to increase the specific surface area of the tungsten compound. is improved and the reactivity with the lithium compound is enhanced, so that the residual amount of the unreacted tungsten compound can be sufficiently reduced.

The average particle size d50 of the tungsten compound is the particle size where the volume of each particle is accumulated from the smaller particle size side, and the cumulative volume is 50% of the total volume of all particles (total volume is 100% When determining the cumulative curve of the particle size distribution, it means the particle size at the point where this cumulative curve reaches 50%), and can be determined from the volume integrated value measured with a laser beam diffraction scattering type particle size analyzer.

In any case, the addition of W is such that the amount of W in the coating of a compound containing W and LI such as lithium tungstate formed on the surface of the particles constituting the positive electrode active material falls within the scope of the present invention. As such, the processing conditions and means of addition must be selected. Since these processing conditions and addition means are known, detailed description thereof will be omitted here.

Preferably, the dry mixing step is carried out for a period of time ranging from 5 minutes to 60 minutes while stirring at a peripheral speed ranging from 5 m/s to 10 m/s. If either the peripheral speed of stirring or the process time in the dry mixing step is below the lower limit, the tungsten compound may not be sufficiently and uniformly dispersed on the surface of the secondary particles of the composite oxide. . On the other hand, if either the circumferential speed of stirring or the process time in the dry mixing process exceeds the upper limit, there is a possibility that the positive electrode active material will be pulverized.

The peripheral speed of stirring in the dry mixing step is more preferably in the range of 6 m/sec to 8 m/sec.

More preferably, the process time of the dry mixing process is in the range of 10 minutes to 30 minutes.

In addition, a general mixer can be used for mixing. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

(2) Second mixing step (lithium compound aqueous solution spray mixing step)
The second mixing step is a step of spraying and mixing an aqueous lithium compound solution instead of conventional water to the mixture of the composite oxide and the tungsten compound thus obtained. As a result, in a mixture in which a tungsten compound is added in an amount of more than 0.4% by mass, preferably 0.7% by mass or more, relative to the total mass of the composite oxide, a sufficient amount relative to the amount of the tungsten compound added is fed through a first mixing step, a dry mixing step, and a second mixing step, an aqueous lithium compound spray mixing step. Therefore, in the presence of water, the neutralization reaction between the surplus lithium such as lithium hydroxide and the tungsten compound such as tungsten oxide, which is liberated on the surface of the primary particles of the composite oxide, can proceed more uniformly and sufficiently. Become. In particular, in combination with regulating the average particle size d50 of the tungsten compound to 70 μm or less, specifically in the range of 0.1 μm to 70 μm, the residual amount of unreacted tungsten compound is made almost zero, or can be brought close to zero.

As described above, excess lithium such as liberated lithium hydroxide is present on the surface of the secondary particles constituting the composite oxide serving as the base material, more specifically, on the surface of the primary particles constituting the secondary particles. In addition, in the dry mixing step, which is the first mixing step, lithium tungstate is used as the tungsten compound, or lithium hydroxide or the like is used as the alkali of the alkaline solution (W) that dissolves the tungsten compound. This provides a lithium compound that reacts with the tungsten compound. However, in the conventional method for producing a positive electrode active material, in the first mixing step, the composite oxide and the tungsten compound are dry-mixed, and in the second step, water is further sprayed and mixed, and then obtained. The resulting mixture is subjected to a drying process.

When tungsten oxide is used as the tungsten compound and water spray mixing is performed in the water spray mixing step, for example, when tungsten oxide, lithium hydroxide and water are mixed, the synthesis reaction proceeds with heat generation, and after the reaction (Li ₂ WO ₄ ).(H ₂ O) ₄ (lithium tungstate hydrate) is obtained, and moisture is lost by heating in the drying step to form a coating of lithium tungstate. The reaction formula is as follows.
_14LiOH.H2O + _7WO3 →7( _Li2WO4 ) _.4 ( _H2O )+ _17H2O

However, according to the findings of the present inventors, in this production method, the mixture is immediately subjected to a drying process after water spray mixing, so that the added tungsten compound is sufficiently on the surface of the positive electrode active material. can not sufficiently react with the excess lithium, and a large amount of unreacted tungsten compound such as tungsten oxide remains. Therefore, the surface of the secondary particles constituting the positive electrode active material is unevenly coated with the compound containing W and Li. Therefore, when the added amount of the tungsten compound to be added exceeds 0.4% by mass, as the added amount increases, the amount of unreacted W such as tungsten oxide simply increases, and W and Li Formation of the coating of the compound containing becomes more uneven, and the resistance of the positive electrode active material tends to increase.

The content of lithium in the lithium compound aqueous solution added in the second mixing step is such that the molar ratio of Li to W in the tungsten compound added in the first mixing step is in the range of 1.2 to 10. is preferably regulated. At a lithium content where the molar ratio of Li to W in the tungsten compound is less than 1.2, the amount of the lithium compound that reacts with the tungsten compound may be insufficient, resulting in a large amount of unreacted tungsten compound. In order to supply a sufficient amount of lithium compound for the reaction with the tungsten compound, the lithium compound is preferably contained in the lithium compound aqueous solution in such an amount that the molar ratio of Li to W in the tungsten compound is 2 or more. preferable.

On the other hand, when the content of the lithium compound exceeds 10 in the molar ratio of Li to W in the tungsten compound, the lithium compound such as lithium hydroxide remains and changes to lithium carbonate (Li ₂ CO ₃ ) or the like, In a lithium ion secondary battery, the positive electrode resistance may increase, and lithium carbonate may react with the electrolyte in the battery to cause the generation of carbon dioxide (CO ₂ ) gas. The content of lithium in the lithium compound aqueous solution is more preferably regulated so that the molar ratio of Li to W in the tungsten compound is 1.5 to 10, and is regulated to be 2 to 8. is more preferred.

In the second mixing step, the lithium compound used as the material constituting the lithium compound aqueous solution is not particularly limited, but due to the ease of availability, lithium hydroxide, lithium nitrate, lithium carbonate, or these Preference is given to using mixtures. In particular, considering the ease of handling and the stability of quality, it is preferable to use lithium hydroxide.

The amount (total amount) of water in the lithium compound aqueous solution added in the second mixing step is in the range of 2% by mass to 30% by mass with respect to the total mass of the mixture obtained in the first mixing step. regulated by That is, if the amount of water to be sprayed is less than 2% by mass with respect to the entire mixture, the effect of adding water may not be sufficiently exhibited, and the tungsten compound may remain. On the other hand, when the amount of water to be sprayed exceeds 30% by mass, the amount of lithium (excess lithium amount) eluted from the composite oxide that is the base material into water becomes excessive during the period from the spraying of the lithium compound aqueous solution to drying, The lithium content in the obtained positive electrode active material may decrease, and the effect of reducing the resistance may not be obtained sufficiently. Moreover, if the amount of water to be sprayed exceeds 30% by mass, a long drying time is required to reduce the moisture content in the obtained positive electrode active material, which may reduce productivity.

From the viewpoint of enabling the lithium compound aqueous solution to be sprayed more uniformly on the surface of the mixture, the amount (total amount) of water in the lithium compound aqueous solution should be 5% by mass to 25% by mass with respect to the total mass of the mixture. is preferred, and 10% by mass to 20% by mass is more preferred.

Pure water is preferably used as water from the viewpoint of avoiding contamination of impurities. In the lithium compound aqueous solution, the added lithium compound dissolves, and the unreacted lithium compound present in the composite oxide and the excess lithium such as excess lithium present in the crystal dissolve. By dissolving a tungsten compound such as tungsten, a coating consisting of fine particles and/or a film of a compound containing W and Li such as lithium tungstate can be formed on at least the surface of the secondary particles constituting the composite oxide. It becomes possible.

The state of the lithium compound aqueous solution during spraying is preferably a mist state with an average particle size of 100 μm or less. When adding the lithium compound aqueous solution in the mist state, the neutralization reaction between the added lithium compound or surplus lithium and the tungsten compound is more uniform on the surface of the primary particles that constitute the surface of at least the secondary particles of the composite oxide. The particle diameter of the fine particles containing W and Li formed at least on the surface of the secondary particles constituting the positive electrode active material or the film thickness of the coating can be set within a suitable range. When the average particle size of the aqueous lithium compound solution to be sprayed is greater than 100 μm, there is a gap between the secondary particles to which the aqueous lithium compound solution is directly supplied by spraying and the secondary particles to which the aqueous lithium compound solution is supplied by stirring after spraying. Different amounts of lithium participating in the reaction may cause heterogeneity in the reaction.

For spraying the lithium compound aqueous solution in the second mixing step, a known spraying device such as a spray dryer can be used. In addition, mixing in the lithium compound aqueous solution spray mixing step, which is the second mixing step, is usually performed manually by an operator using a spatula because it is sufficient for the sprayed lithium compound aqueous solution to spread throughout the mixture. However, it is also possible to perform mixing using a mixer under stirring conditions conforming to the dry mixing process.

In the lithium compound aqueous solution spray mixing step, which is the second mixing step, the lithium compound aqueous solution spray is stirred at a peripheral speed in the range of 5 m / sec to 10 m / sec, and is in the range of 50 ml / min to 100 ml / min. A water spray rate is preferred. Further, it is preferable that the mixing after completion of the lithium compound aqueous solution spraying is continued for a time in the range of 5 to 60 minutes while stirring at a peripheral speed in the range of 5 m/s to 10 m/s.

In the lithium compound aqueous solution spray mixing step, if any of the peripheral speed of stirring, the spray speed, and the process time is below the lower limit, the reaction between the tungsten compound and the lithium compound on the surface of the secondary particles of the composite oxide will occur. You may not be able to do enough. On the other hand, if any of the circumferential speed of stirring, the spraying speed, and the process time in the step of spraying and mixing the aqueous lithium compound solution exceeds the upper limit, there is a possibility that the positive electrode active material will be pulverized.

In the step of spraying and mixing the lithium compound aqueous solution, the peripheral speed of stirring is more preferably in the range of 6 m/sec to 8 m/sec both during spraying and during mixing after spraying.

In the lithium compound aqueous solution spray mixing step, the water spray rate is preferably in the range of 60 ml/min to 90 ml/min, more preferably in the range of 65 ml/min to 85 ml/min.

The process time for water spraying is defined by the amount of water to be sprayed and the speed of water spraying, but is preferably in the range of 5 minutes to 25 minutes, more preferably in the range of 10 minutes to 26 minutes.

In the step of spraying and mixing the lithium compound aqueous solution, the step time for mixing after spraying is more preferably in the range of 10 to 30 minutes.

A general mixer can also be used for mixing in the lithium compound aqueous solution spray mixing step. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

(3) Drying step A step of drying a mixture obtained by spraying an aqueous solution of a lithium compound to a mixture of a composite oxide and a tungsten compound to obtain a compound-coated composite oxide containing W and Li.

In the lithium compound aqueous solution spray mixing step, which is the second mixing step, in the presence of water, a tungsten compound such as tungsten oxide reacts with lithium in the added lithium compound and excess lithium in the base material composite oxide. As a result, a hydrate of a compound containing W and Li, such as lithium tungstate hydrate, is present on at least the surfaces of the secondary particles of the composite oxide. The heating in the drying step reduces the water content in the composite oxide and removes the water content from the hydrate of the compound containing W and Li, so that lithium tungstate is formed on at least the surface of the secondary particles of the composite oxide. A coating consisting of fine particles and/or a film of a compound containing W and Li such as is formed.

The drying temperature is not particularly limited as long as the moisture content is sufficiently reduced, but it is preferable to dry at a temperature of 500° C. or less. If the drying temperature exceeds 500° C., lithium is further liberated from the interior of the primary particles, resulting in insufficient slurry stability. Although the lower limit of the drying temperature is not particularly limited, it is preferably 100° C. or higher from the viewpoint of shortening the treatment time and sufficiently removing water from the hydrate of the compound containing W and Li. Moreover, the pressure during drying is desirably 1 atm or less. If the pressure is higher than 1 atm, there is a possibility that the moisture content may not sufficiently decrease. The drying time is not particularly limited as long as the moisture content is sufficiently reduced. For example, it can be about 5 hours or more and 24 hours or less.

The drying process can be performed using a known dryer such as a flash dryer, an indirect heating dryer, and a vacuum dryer.

(4) Settling step In the present invention, after the lithium compound aqueous solution spray mixing step and before the drying step, the mixture is heated at a temperature in the range of 30 ° C. to 80 ° C. for 1 hour to 2 hours. It is preferable to provide a standing step of standing for a time within a time range.

By providing such a standing step, the reaction between the tungsten compound such as tungsten oxide and the lithium compound such as lithium hydroxide can be matured, so that the reactivity between the tungsten compound and the lithium compound is further improved. It is possible to In particular, by regulating the average particle size d50 of the tungsten compound to 70 μm or less, specifically in the range of 0.1 μm to 70 μm, and combining with the lithium compound aqueous solution spray mixing, the residual amount of unreacted tungsten compound can be made almost zero, or brought close to almost zero.

If the heating temperature of the mixture in the standing step is less than 30° C. or the standing time is less than 1 hour, the effect of aging the reaction between the tungsten compound and the lithium compound may not be sufficiently obtained. On the other hand, if the heating temperature of the mixing section exceeds 80° C. or the standing time exceeds 2 hours, the positive electrode active material may be damaged. From this point of view, the temperature for heating the mixture in the standing step is more preferably in the range of 30°C to 50°C, more preferably in the range of 40°C to 45°C. Further, the standing time is more preferably in the range of 1.5 hours to 2 hours.

The standing step can also be performed using a known dryer such as a flash dryer, an indirect heating dryer, and a vacuum dryer, as in the drying step.

(5) Additional mixing step (third mixing step)
After the step of spraying and mixing the aqueous lithium compound solution, or after the step of standing if a step of standing is provided, and before the drying step, the mixture is stirred at a speed in the range of 5 m / sec to 10 m / sec. It is preferable to provide an additional mixing step (third mixing step) in which mixing is performed for a period of time ranging from 5 minutes to 60 minutes while stirring at a peripheral speed.

By providing an additional mixing step, it is possible to improve the particle dispersibility of the tungsten compound adhering to the surface of the secondary particles constituting the composite oxide of the mixture, thereby making W and Li more uniform. Since it is possible to form a coating with fine particles and/or a film of the compound contained, the positive electrode interfacial resistance can be further reduced, and the output of the positive electrode active material can be increased.

If the peripheral speed when stirring the mixture is less than 5 m / sec, or the mixing time is less than 5 minutes, there is a possibility that the dispersibility of the tungsten compound cannot be sufficiently improved by providing an additional mixing step. . On the other hand, if the peripheral speed when stirring the mixture exceeds 10 m/sec, or if the mixing time exceeds 60 minutes, there is a possibility that the positive electrode active material will be pulverized. From this point of view, it is more preferable to set the peripheral speed at which the mixture is stirred in the range of 6 m/sec to 8 m/sec. Further, it is more preferable to set the mixing time in the additional mixing step to the range of 10 minutes to 30 minutes.

The mixing in the additional mixing step, which is the third mixing step, can be performed using the mixer shown in the dry mixing step.

(6) Difference in average particle size MV of secondary particles before and after compound coating containing W and Li The ratio of the average particle size MV of the secondary particles constituting the positive electrode active material coated with the compound containing W and Li to the average particle size MV of the secondary particles is 90% or more. This ratio is preferably 95% or more.

In the present invention, when the compound coating containing W and Li is formed on the base material, the secondary particles of the base material are hardly pulverized because the strength of the secondary particles of the base material is high. For this reason, the average particle diameter MV of the secondary particles of the base material, [(d90-d10) / average particle diameter MV], which is an index showing the spread of the particle size distribution of the secondary particles, and the tap density are the The properties are generally inherited, and in particular, the decrease in the average particle size MV is suppressed.

(7) Method for Producing Lithium-Nickel-Manganese-Cobalt-Containing Composite Oxide as Base Material In the method for producing a positive electrode active material for a lithium-ion secondary battery of the present invention, the base material is a ternary composite oxide having a porous structure. That is, it is composed of secondary particles formed by aggregating a plurality of primary particles, and the secondary particles are present in the outer shell formed by the agglomerated primary particles and inside the outer shell. a porous structure comprising: agglomerated portions formed by the agglomerated primary particles and electrically connected to the outer shell portion; and space portions dispersed in the agglomerated portions. However, the method for producing this composite oxide is not limited.

However, a method for producing such a composite oxide having a porous structure will be briefly described below.

(7-1) Method for producing nickel-manganese-cobalt-containing composite hydroxide It inherits the particle structure of the "thing"). A composite hydroxide having this particle structure is preferably produced by the following crystallization reaction.

(a) Crystallization reaction Composite hydroxide forms a reaction aqueous solution by supplying a raw material aqueous solution containing at least a transition metal and an aqueous solution containing an ammonium ion donor into a reaction vessel, and the crystallization reaction can get.

The step of carrying out a crystallization reaction includes a nucleation step of nucleation 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 pH value of the reaction aqueous solution containing nuclei obtained in the generation step is controlled to be lower than the pH value in the nucleation step and in the range of 10.5 to 12.0 at a liquid temperature of 25 ° C. and a grain growth step for growing the nuclei.

(1) adjusting the reaction atmosphere in the first stage (initial stage) of the nucleation step and the grain growth step to a non-oxidizing atmosphere having an oxygen concentration of 2% by volume or less; After the first step, the reaction atmosphere is switched from the non-oxidizing atmosphere to an oxidizing atmosphere having an oxygen concentration of more than 2% by volume and not more than 5% by volume as the second step of the grain growth step, ( 3) Next, the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere to perform the third stage of the grain growth process, and (4) the reaction atmosphere is further changed from the non-oxidizing atmosphere. (5) Finally, the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere to perform the fifth step of the grain growth step. step by step.

For the ratio of the crystallization reaction in each stage to the entire grain growth process, 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. , 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%. , the fifth stage is preferably 10% to 50%.

[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 2% 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, the reaction atmosphere is changed from a non-oxidizing atmosphere to an oxygen atmosphere by introducing an atmosphere gas while continuing to supply the raw material aqueous solution in the middle of the particle growth step. An operation is performed to switch to an oxidizing atmosphere with a concentration exceeding 2% by volume and 5% by volume or less, or to switch from this non-oxidizing atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less.

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. As a result, the atmosphere switching time can be shortened, and the size of the central portion, the thicknesses of the first low-density layer, the high-density layer, the second low-density layer, and the outer shell layer are appropriately set. 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 is prevented, and the particle size distribution of the secondary particles of the obtained composite hydroxide is 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 can be controlled by 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. 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. .

(7-2) Supply aqueous solution a) Raw material aqueous solution In the present invention, the ratio of the metal elements contained in the raw material aqueous solution is generally the composition ratio of the resulting composite hydroxide.

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 a 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.

In addition, the supply amount of the raw material aqueous solution is such that the concentration of the product in the aqueous solution for particle growth 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. be.

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.

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 Aqueous solution containing ammonium ion donor is not particularly limited, for example, ammonia water, or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride is used. can do.

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.

[Reaction atmosphere]
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 becomes a non-oxidizing atmosphere of 2% by volume or less, preferably 1% by volume or less. Control to a mixed atmosphere of oxygen and inert gas.

b) Oxidizing Atmosphere On the other hand, in the step of forming the first low-density layer and the second low-density layer 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 2% by volume and be 5% by volume or less, preferably 3% by volume or more. By controlling the oxygen concentration in the reaction atmosphere to such a range, particle growth is suppressed and the average particle size of the fine primary particles is in the range of 0.02 μm to 0.3 μm. , and a first low density layer and a second low density layer having a sufficient density difference with the outer shell layer. When the oxygen concentration in the reaction atmosphere exceeds 5% by volume, the average particle diameter of the fine primary particles is less than 0.02 μm in the ternary composite hydroxide containing at least nickel, manganese, and cobalt. As a result, the total amount of fine primary particles absorbed in the high-density layer and the outer shell layer becomes insufficient, and in the lithium-nickel-manganese-cobalt-containing composite oxide obtained using such a composite hydroxide as a precursor, The improvement of the particle strength cannot be sufficiently achieved. On the other hand, when the oxygen concentration in the reaction atmosphere is 2 volumes or less, the average particle diameter of the fine primary particles exceeds 0.3 μm, and the plate-like primary particles constituting the central portion, the high-density layer and the outer shell layer , the difference in particle diameter between the fine primary particles constituting the first low-density layer and the second low-density layer becomes too small, and the low-density layer shrinks, resulting in insufficient space formation. may become

For the same reason, the difference in oxygen concentration between the non-oxidizing atmosphere and the oxidizing atmosphere is preferably 1.0% by volume or more, more preferably 2.0% by volume or more.

c) Switching of reaction atmosphere The crystallization reaction in the non-oxidizing atmosphere in the first stage (initial stage) of the grain growth stage is preferably in the range of 8% 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 and the fourth stage should preferably be within the range of 4% to 45%, more preferably within the range of 5% to 35%.

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 50% of the total grain growth process time, More preferably, the range is from 25% to 45% to form a sufficient skeleton of the outer shell. 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

By such a crystallization reaction,
Consisting of a plurality of plate-shaped primary particles and secondary particles formed by aggregation of fine primary particles smaller than the plate-shaped primary particles,
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 and an outer shell layer formed mainly by aggregation of the plate-like primary particles outside the second low-density layer, and
The tap density is 0.95 g/cm ³ or more,
The average particle diameter MV of the secondary particles is in the range of 3 μm to 12 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. is less than or equal to .65;
A composite hydroxide is obtained.

(8) Method for producing a lithium-nickel-manganese-cobalt-containing composite oxide as a base material The composite oxide as a base material comprises a mixing step of mixing the composite hydroxide and a lithium compound to form a lithium mixture; It is obtained by 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.

(8-1) Heat treatment step This is an optional step, in which the composite hydroxide is converted into heat treated particles (composite hydroxide from which excess moisture has been removed and/or oxides) before mixing with the lithium compound. compound oxide).

The heat treatment temperature is in the range of 105° C. to 750° C., whereby the moisture remaining in the heat-treated particles until after the firing process can be reduced to a certain amount, and the composition of the composite oxide that is the base material obtained can be reduced. can be suppressed.

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

(8-2) Mixing Step The mixing step is a step of mixing the composite hydroxide or heat-treated particles with a lithium compound to obtain a lithium mixture.

In the mixing step, the ratio (Li/ Complex water such that Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, still more preferably 1.0 to 1.2 The oxide or heat treated particles are mixed with the lithium compound.

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.

(8-3) 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 350 C. to 800.degree. C., preferably 450.degree. C. to 780.degree. 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 to 10 hours, more preferably 3 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.

(8-4) Firing step In the firing step, the lithium mixture obtained in the mixing step is fired under predetermined conditions to diffuse lithium into the composite hydroxide or heat-treated particles to obtain a lithium composite oxide. is.

In this sintering step, the composite hydroxide and the central portion of the heat-treated particles, the high-density layer, and the plate-like primary particles that make up the high-density layer 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 composite oxide 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, but it is preferable to use a batch-type or continuous-type electric furnace. The same applies to the 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 agglomerated parts and the space part that constitute the secondary particles, respectively, the lithium mixture is preferably sintered at a temperature of 700°C to 920°C, more preferably 750°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 held at a temperature near the melting point of the lithium compound, preferably for 1 to 5 hours, more preferably for 2 to 5 hours.

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 33° C./min to 77° C./min.

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. (atmosphere or oxygen stream) is particularly preferred. If the oxygen concentration is less than 18% by volume, the crystallinity of the positive electrode active material may be insufficient.

(8-5) Crushing step The secondary particles that make up the composite oxide obtained in the firing step are optionally crushed to crush the aggregates or sintered bodies when agglomeration or mild sintering occurs. It is a process. Thereby, the average particle size and particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range.

The pulverization is performed by adjusting the pulverization force to an appropriate range using a known means such as a pin mill or a hammer mill so as not to destroy the secondary particles.

3. 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. 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, conductive material and 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 lithium-containing substances such as metal lithium and lithium alloys, natural graphite and artificial graphite that can occlude and desorb lithium ions, organic compound sintered bodies such as phenolic resins, and carbon substances such as coke. 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 In the lithium ion secondary battery of the present invention, as described above, the compound containing W and Li of the present invention is more uniformly coated on at least the surface of the secondary particles. Since it has a porous structure and uses a ternary positive electrode active material as a positive electrode material, it has excellent capacity characteristics, output characteristics, and cycle characteristics. Therefore, a ternary positive electrode active material having a porous structure without a conventional coating of a compound containing W and Li, and a ternary positive electrode having a coating of a compound containing W and Li but not having a porous structure A lithium-ion secondary battery using a ternary positive electrode active material, which has a coating of an active material or a compound containing W and Li and has a porous structure, but the coating is not uniformly formed. In comparison, it is possible to exhibit battery characteristics such as lower resistance and higher output.

(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=1:1:1 to prepare a 2 mol/L raw material aqueous solution. .

Next, the raw material aqueous solution was supplied to the pre-reaction aqueous solution at 115 ml/min to form an aqueous solution for nucleation , 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 reached a predetermined value, the raw material aqueous solution was supplied at a constant rate of 115 ml/min, the same as in the nucleation step, to grow the nuclei (particles) generated in the nucleation step. .

As a first step, after continuing crystallization in a non-oxidizing atmosphere for 35 minutes (14.6% of the entire grain growth process) from the start of the grain growth process, while continuing to supply the raw material aqueous solution, Air was 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, and the reaction atmosphere was adjusted to an oxidizing atmosphere with an oxygen concentration of 5% by volume ( switching operation 1).

As a second step, after continuing crystallization in an oxidizing atmosphere from switching operation 1 for 20 minutes (8.3% of the entire grain growth process), an air diffuser was used while continuing to supply the raw material aqueous solution. The reaction atmosphere was adjusted to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less (switching operation 2).

As the third step, after continuing crystallization in a non-oxidizing atmosphere from switching operation 2 for 65 minutes (27.1% of the entire grain growth process), the air diffuser was turned on while continuing to supply the raw material aqueous solution. was used to circulate air in the reaction tank to adjust the atmosphere to an oxidizing atmosphere with an oxygen concentration of 5% by volume (switching operation 3).

As the fourth step, after the crystallization reaction in the oxidizing atmosphere was continued for 40 minutes (16.7% of the entire grain growth process) from the switching operation 3, the air diffuser was turned on while continuing to supply the raw material aqueous solution. was used to circulate nitrogen in the reaction tank to adjust the reaction atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less (switching operation 4).

As a fifth step, after the crystallization reaction in the non-oxidizing atmosphere continues for 80 minutes (33.3% of the entire grain growth process) from the switching operation 4, the supply of all the aqueous solutions including the raw material aqueous solution is stopped. By doing so, the grain growth process was completed. 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 25.0%.

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 _0.33 Mn _0.33 Co _0.33 (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 Also, it was confirmed that some of the plate-like primary particles constituting the core, high-density layer, and outer shell layer were interconnected. Measure the maximum outer diameter (major axis diameter) of 10 or more fine primary particles and plate-shaped primary particles present in the cross section of the secondary particles, determine the average value, and use this value as the fine primary particles in the secondary particles Particles or plate-like primary particles, and then for 10 or more secondary particles, similarly determine the particle sizes of fine primary particles and plate-like primary particles, and obtain the particle sizes of these secondary particles. was calculated as the average of The plate-like primary particles had an average particle size of 0.53 μm, and the fine primary particles had an average particle size of 0.09 μm.

The ratio of the radius of the central part and 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 was also measured and calculated. Whereas 25%, 10%, 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.

[Tap density]
The tap density was measured with a tapping machine (KRS-406, manufactured by Kuramochi Scientific Instruments Co., Ltd.). As a result, it was confirmed that the tap density was 1.05 g/cm ³ .

c) Preparation of composite oxide 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 device (TURBULA Type T2C manufactured by Willie & Bacchofen (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 lithium-nickel-manganese-cobalt-containing composite oxide thus obtained. Therefore, this composite oxide was pulverized to adjust the average particle size and particle size distribution (pulverization step).

d) Evaluation of composite oxide [Composition]
Analysis using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPE-9000) revealed that the composition of this composite oxide has the general formula: Li _1.10 Ni _0.33 Mn _0.33 Co _0.33 O ₂ was confirmed.

[Particle structure]
Part of the composite oxide is embedded in a resin, cross-sectionally observable by processing a cross section polisher (manufactured by JEOL Ltd., IB-19530CP), and then SEM (FE-SEM: manufactured by JEOL Ltd., JSM -6360LA). As a result, the composite oxide is composed of secondary particles formed by agglomeration 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.

[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 oxide is measured, and d10 and d90 are measured, and the particle size is measured. [(d90-d10)/average particle size MV], which is an index showing the spread of the distribution, was calculated. As a result, it was confirmed that the average particle diameter MV was 5.0 μm and [(d90−d10)/average particle diameter MV] was 0.42.

[BET specific surface area, tap density, and particle strength]
The BET specific surface area is determined by a flow-type gas adsorption method specific surface area measuring device (manufactured by Mountec Co., Ltd., Macsorb 1200 series), the tap density is determined by a tapping machine (manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd., KRS-406), and the microparticle compression tester. (manufactured by Shimadzu Corporation, MCTM-500) to measure the particle strength. As a result, it was confirmed that the BET specific surface area was 3.0 m ² /g, the tap density was 1.4 g/cm ³ and the particle strength was 27 MPa.

e) Preparation of positive electrode active material As a tungsten compound, tungsten oxide having an average particle size d50 of 40 μm measured using a laser diffraction/scattering particle size distribution analyzer (manufactured by Microtrack Bell Co., Ltd., Microtrac MT3300EXII) ( _WO3 ) was used.

A composite oxide (3000 g) is used as a base material, and the amount of tungsten oxide (with respect to the composite oxide) is 0.35 atomic% with respect to the total number of atoms of Ni, Mn, and Co contained in the composite oxide. 0.9% by mass), and using a shaker mixer device (TURBULA Type T2C manufactured by Willie & Bachoffen (WAB)), the composite oxide and tungsten oxide are mixed at a peripheral speed of 8 m / sec for 10 minutes. They were thoroughly mixed to obtain a mixture (first mixing step: dry mixing step).

With respect to the W amount of tungsten oxide added in the first mixing step, the amount of lithium hydroxide that makes the molar ratio of Li to 2 and the amount of 20% by mass with respect to the mixture obtained in the first mixing step Pure water was prepared to prepare an aqueous lithium hydroxide solution.

Using a water spray device (manufactured by Yamato Scientific Co., Ltd., spray dryer DL410) and a shaker mixer device (TURBULA Type T2C manufactured by Willie & Bachoffen (WAB)), a lithium hydroxide aqueous solution is dispersed in a mist state with an average particle size of 100 μm or less. Then, the mixture obtained in the first mixing step is sprayed at a spray rate of 50 ml/min for 5 minutes while stirring the mixture at a peripheral speed of 8 m/sec, and after spraying is completed, 8 m/sec (second mixing step: lithium compound aqueous solution spray mixing step) for 10 minutes at a peripheral speed of . After the lithium hydroxide aqueous solution was sprayed and mixed, a part of the mixture was used as a sample and the moisture content was measured, and the moisture content was 7.5% by mass.

After the second mixing step was completed, the mixture was heated to 45 ° C. using a dryer (Nitrogen purge type vacuum dryer manufactured by Shimakawa Seisakusho Co., Ltd.) and allowed to stand for 1.5 hours (standing step ).

Furthermore, after the stationary step, the mixture was mixed for 20 minutes at a peripheral speed of 8 m / sec using a shaker mixer device (TURBULA Type T2C manufactured by Willie & Bakkofen (WAB)) (third mixing process: additional mixing process).

After the third mixing step, the above mixture was dried at 150° C. for 12 hours using a dryer (Nitrogen purge type vacuum dryer manufactured by Shimakawa Seisakusho Co., Ltd.) to obtain a positive electrode active material. No fine powder was found in the positive electrode active material. After that, the obtained positive electrode active material was sieved under the condition of a sieve mesh of 38 μm.

f) Evaluation of Positive Electrode Active Material [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, the average particle size MV was 4.8 μm (ratio to the average particle size MV of the composite oxide before the compound coating containing W and Li: 96%), [(d90-d10)/average particle size MV ] was confirmed to be 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 3.2 m ² /g and the tap density was 1.4 g/cm ³ .

[composition]
The composition of the obtained positive electrode active material was analyzed by ICP emission spectrometry, and it was confirmed that the W content was 0.35 atomic % with respect to the total number of atoms of Ni, Mn and Co.

[Coating (fine particles and/or coating)]
From the results of single-color powder XRD analysis using an X-ray diffraction (XRD) device (X'Pert PRO manufactured by Spectris Co., Ltd.), the coating of the compound containing W and Li on the surface of the secondary particles is that of lithium tungstate. It was confirmed to consist of a hydrate (7Li ₂ WO _{4.4H 2} O). Also, no peak of tungsten oxide (WO ₃ ) was confirmed.

After the positive electrode active material is in a state where cross-sectional observation is possible with a scanning transmission electron microscope (STEM: Hitachi High-Technologies Co., Ltd., scanning electron microscope S-4700), the vicinity of the surface of the secondary particles is observed with STEM. As a result, it was confirmed that fine particles having an average particle diameter of 56 nm and a particle diameter ranging from 21 nm to 279 nm and a coating having a thickness of about 2 nm were uniformly formed on the surfaces of the secondary particles. Also, using an X-ray photoelectron spectroscopy (XPS) device (manufactured by VG-Scientific, ESCALab220i-XL), target: Al, X-ray source: Al-Kα ray, voltage: 10 kV, current: 15 mA, 10 pieces XPS spectra of W, Ni, Mn, and Co were measured for each of the secondary particles of , and the ratio of their peak intensities was obtained. Based on the abundance ratio of W (W / (W + Ni + Mn + Co), the coverage of the compound of W and Li was calculated and the average was obtained. As a result, the coverage of the compound of W and Li was 70%. .

g) Production of Secondary Battery A 2032-type coin battery 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 11 was produced by drying at 120° C. for 12 hours in a vacuum dryer.

Next, using this positive electrode 11, 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 12 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 13 . Thus, a 2032-type coin battery having a gasket 14 and including a cathode can 15 and an anode can 16 was assembled.

h) 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). A Nyquist plot 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 2, which will be 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 0.68 times that of Comparative Example 2.

[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 89%.

Conditions in the manufacturing process of the positive electrode active material, average particle size MV of the secondary particles of the positive electrode active material, BET specific surface area, tap density, lithium tungstate coverage, presence or absence of tungsten oxide, and obtained lithium ions Tables 1 and 2 show the positive electrode interfacial resistance and the discharge capacity retention rate of the secondary batteries. Examples 2 to 7 and Comparative Examples 1 to 3 are also shown in Tables 1 and 2.

(Example 2)
A positive electrode active material was obtained in the same manner as in Example 1, except that the amount of lithium hydroxide in the lithium hydroxide aqueous solution was such that the molar ratio of Li to the amount of W in tungsten oxide was 5. , made its evaluation.

(Example 3)
A positive electrode active material was obtained in the same manner as in Example 1, except that the amount of lithium hydroxide in the lithium hydroxide aqueous solution was such that the molar ratio of Li to the amount of W in tungsten oxide was 8. , made its evaluation.

(Example 4)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the mixture was dried after the standing step without providing an additional mixing step.

(Example 5)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that an additional mixing step was performed after the lithium compound aqueous solution spray mixing step without providing the standing step.

(Example 6)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the mixture was dried after the lithium compound aqueous solution spray mixing step without providing the stationary step and the additional mixing step. rice field.

(Example 7)
A positive electrode active material was obtained in the same manner as in Example 1, except that tungsten oxide having an average particle size d50 of 50 μm using a laser diffraction scattering particle size analyzer was used as the tungsten compound, and the evaluation was performed. gone.

(Example 8)
Other than adding tungsten oxide with a W amount of 1.9 atomic % (5.0 mass % with respect to the composite oxide) with respect to the total number of atoms of Ni, Mn, and Co contained in the composite oxide obtained a positive electrode active material in the same manner as in Example 1 and evaluated it.

(Comparative example 1)
As the tungsten compound, tungsten oxide having an average particle size d50 of 80 μm using a laser diffraction scattering particle size analyzer, and in the lithium compound aqueous solution spray mixing step, without adding lithium hydroxide, the second 10% by mass of pure water with respect to the mixture obtained in the first mixing step in a mist state with an average particle size of 100 μm or less, and the mixture obtained in the first mixing step is spun at a circumference of 8 m / sec. While stirring the mixture at high speed, it was sprayed for 10 minutes, and after spraying was completed, mixing was continued for 5 minutes at a peripheral speed of 8 m / second, and then the mixture was subjected to a drying process without standing still. obtained a positive electrode active material in the same manner as in Example 1 and evaluated it.

(Comparative example 2)
In the lithium compound aqueous solution spray mixing step, 35% by mass of pure water is added to the mixture obtained in the first mixing step in a mist state with an average particle size of 100 μm or less without adding lithium hydroxide. The mixture obtained in the mixing step 1 is sprayed for 10 minutes while being stirred at a peripheral speed of 8 m/sec, and after the spraying is completed, mixing is continued for 5 minutes at a peripheral speed of 10 m/sec. After that, a positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the mixture was subjected to the drying step without being allowed to stand still.

(Comparative Example 3)
A positive electrode active material was prepared in the same manner as in Example 1, except that the step of applying a compound coating containing W and Li to the base material in Example 1 was omitted, and the composite oxide of the base material was used as the positive electrode active material. obtained and evaluated.

In the lithium ion secondary batteries using the positive electrode active materials of Examples 1 to 7, which are within the scope of the present invention, in comparison with Comparative Examples 1 to 3, the positive electrode interfacial resistance decreased, It was confirmed that high output was achieved.

REFERENCE SIGNS LIST 1 outer shell portion 2 aggregation portion 3 space portion 4 fine particles of a compound containing W and Li 5 coating of a compound containing W and Li 11 positive electrode (evaluation electrode)
12 negative electrode 13 separator 14 gasket 15 positive electrode can 16 negative electrode can

Claims (20)

Consists of secondary particles formed by agglomeration of a plurality of primary particles, and a coating of fine particles and/or a coating of a compound containing W and Li is present on at least the surface of the secondary particles, containing W and Li. A positive electrode active material for a lithium ion secondary battery comprising a compound-coated lithium-nickel-manganese-cobalt-containing composite oxide containing
The secondary particles are present in an outer shell portion formed of the aggregated primary particles, and inside the outer shell portion, are formed of the aggregated primary particles, and are electrically conductive to the outer shell portion. and a space portion dispersed in the aggregation portion,
Based on the XPS spectrum obtained by the surface analysis of the secondary particles by X-ray photoelectron spectroscopy, the coverage of the compound containing W and Li present on the surface of the secondary particles is in the range of 5% to 80%. is characterized by
Positive electrode active material for lithium ion secondary batteries. 2. The cathode active material for a lithium ion secondary battery according to claim 1, wherein said fine particles have a size in the range of 5 nm to 400 nm, and said film has a thickness in the range of 1 nm to 200 nm. 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. 3. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, which is 0.70 or less. 4. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the thickness of the outer shell portion of said secondary particles is in the range of 0.1 μm to 1.0 μm. 5. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein said positive electrode active material has a tap density in the range of 1.0 g/cm ³ to 1.8 g/cm ³ . 6. The positive electrode active material for a lithium ion secondary battery according to claim 1, 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. General formula (A) _: Li1 _{+ uNixMnyCozWsMtO2} (-0.05≤u≤0.50 _{, x} +y+z+s+t=1 _, 0.3≤x≤0.7 _, 0.15≤ y ≤ 0.4, 0.15 ≤ z ≤ 0.4, 0.001 ≤ s ≤ 0.03, 0 ≤ t ≤ 0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr , Nb, Mo, Hf, Ta, W), and is composed of a lithium-nickel-manganese-cobalt-containing composite oxide having a hexagonal layered rocksalt crystal structure. 7. The positive electrode active material for a lithium ion secondary battery according to any one of 6. It is composed of secondary particles formed by aggregating a plurality of primary particles, and the secondary particles are present inside the outer shell formed by the agglomerated primary particles and the outer shell, and the agglomerated It has a porous structure that is formed of primary particles and has an aggregated portion that is electrically connected to the outer shell portion, and a space that exists dispersedly in the aggregated portion. , a lithium-nickel-manganese-cobalt-containing composite oxide, which is a base material, is mixed with a tungsten compound in an amount in the range of more than 0.4% by mass and 5% by mass or less with respect to the total mass of the composite oxide. , a dry mixing process to obtain a mixture,
The mixture contains a lithium compound in an amount such that the molar ratio of Li to W in the tungsten compound is 1.2 or more, and an amount of water in the range of 2% to 30% by mass relative to the total mass of the mixture. A lithium compound aqueous solution spray mixing step of spraying the lithium compound aqueous solution and further mixing the mixture, and
A compound containing W and Li, wherein the mixture is heat-treated at a temperature of 500° C. or less to dry the mixture, and a coating consisting of fine particles and/or a coating of the compound containing W and Li is present on the surface of the primary particles. a drying step for obtaining a coated lithium-nickel-manganese-cobalt-containing composite oxide;
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: 9. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8, wherein the mixed amount of said tungsten compound is 0.7% by mass or more with respect to the total mass of said composite oxide. 10. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8, wherein said tungsten compound is tungsten oxide. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 10, wherein said tungsten compound has an average particle size d50 in the range of 0.1 µm to 70 µm. The lithium ion according to any one of claims 8 to 11, wherein the aqueous solution of the lithium compound contains the lithium compound in an amount such that the molar ratio of Li to W in the tungsten compound is in the range of 1.2 to 10. A method for producing a positive electrode active material for a secondary battery. The lithium ion secondary battery according to any one of claims 8 to 12, wherein the lithium compound aqueous solution contains water in an amount ranging from 5% by mass to 25% by mass with respect to the total mass of the mixture. A method for producing a positive electrode active material for The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 13, wherein the lithium compound is lithium hydroxide. The lithium ion secondary battery according to any one of claims 8 to 14, wherein the dry mixing step is performed for a time ranging from 5 minutes to 60 minutes while stirring at a peripheral speed ranging from 5 m / sec to 10 m / sec. A method for producing a positive electrode active material for a secondary battery. In the lithium compound aqueous solution spray mixing step, while stirring at a peripheral speed in the range of 5 m / sec to 10 m / sec, the lithium compound aqueous solution is sprayed at a spray speed in the range of 50 ml / min to 100 ml / min. The lithium ion secondary battery according to any one of claims 8 to 15, wherein the mixing is continued for a time in the range of 5 minutes to 60 minutes while stirring at a peripheral speed in the range of 5 m / sec to 10 m / sec. A method for producing a positive electrode active material. After the lithium compound aqueous solution spray mixing step and before the drying step, the mixture is heated at a temperature in the range of 50 ° C. to 80 ° C. for 1.5 hours to 2 hours. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 16, comprising a step of standing still for a period of time. After the lithium compound aqueous solution spray mixing step or the standing step and before the drying step, the mixture is stirred at a peripheral speed in the range of 5 m / sec to 10 m / sec for 5 minutes to 5 minutes. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 17, comprising an additional mixing step of mixing for a time in the range of 60 minutes. The _positive electrode _active material for _a lithium ion secondary battery has a general formula (A ₎ : Li1 _{+ uNixMnyCozWsMtO2} (-0.05≤u≤0.50, x+y+z+s+t=1 _, 0. 3≤x≤0.7, 0.15≤y≤0.4, 0.15≤z≤0.4, 0.001≤s≤0.03, 0≤t≤0.1, M is Mg , Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), and lithium nickel manganese having a crystal structure of a hexagonal layered rock salt structure The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 8 to 18, comprising a cobalt-containing composite oxide. 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, the lithium ion secondary according to any one of claims 1 to 7. A lithium ion secondary battery using a battery positive electrode active material.

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