JP2021018982A - Positive electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Abstract

To provide: a positive electrode active material for a lithium ion secondary battery, which is low in positive electrode resistance and high in discharge capacity retention rate when used for a lithium ion secondary battery, and a method for producing the same; and a lithium ion secondary battery having a positive electrode containing the positive electrode active material for a lithium ion secondary battery.SOLUTION: There is provided a positive electrode active material for a lithium ion secondary battery in which base material powder is used as a raw material, the base material powder containing a secondary particle formed by the aggregation of primary particles of a lithium metal composite oxide that contains lithium, nickel and cobalt. A coating layer containing at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate is formed on the surface of the secondary particle. The average thickness of the coating layer is 3-150 nm, and the coefficient of variation (CV%) showing a variation in the thickness of the coating layer is 15% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a positive electrode active material for a lithium ion secondary battery and a method for producing the same. More specifically, the present invention relates to a positive electrode active material for a lithium ion secondary battery having a low positive electrode resistance and a high retention rate of discharge capacity when used in a lithium ion secondary battery, a method for producing the same, and the lithium ion secondary. The present invention relates to a lithium ion secondary battery having a positive electrode containing a positive electrode active material for a battery.

In recent years, from the viewpoint of protecting the global environment, environmentally friendly vehicles such as hybrid vehicles and plug-in hybrid vehicles, which emit less carbon dioxide, are becoming widespread. Among the batteries used in environmental vehicles, the development of lithium-ion secondary batteries is desired because of their excellent output characteristics and charge / discharge cycle characteristics.

As the lithium ion secondary battery, a non-aqueous electrolyte secondary battery in which an organic solvent electrolyte (electrolyte solution) is generally used and an all-solid-state battery in which a nonflammable solid electrolyte is used are generally known. However, a non-aqueous electrolyte secondary battery using an organic solvent electrolyte (electrolyte solution) is flammable and therefore requires safety measures. On the other hand, an all-solid-state battery in which a nonflammable solid electrolyte is used has an advantage that it does not require safety measures like an organic solvent electrolyte (electrolyte solution) because the solid electrolyte is nonflammable.

An all-solid-state battery using a nonflammable solid electrolyte is composed of a positive electrode, a negative electrode, a lithium ion conductive solid electrolyte, and the like. As the active material of the positive electrode and the negative electrode, a material capable of desorbing and inserting lithium is generally used. Among the all-solid-state batteries in which the material is used, the all-solid-state battery in which the layered or spinel-type lithium metal composite oxide is used as the positive electrode active material can obtain an electromotive force of 4.5 V or more. It is expected as a battery with high energy density. However, in the all-solid-state battery, the lithium ion conductive solid electrolyte and the positive electrode active material react at the interface between the two to form a heterogeneous interface, and the diffusion of lithium ions is hindered at the heterogeneous interface, resulting in electrical resistance. Since it rises, there is a drawback that the output characteristics of the battery deteriorate.

As a coating active material capable of suppressing an increase in interfacial resistance between the active material and the solid electrolyte material, a material having an active material and a coating layer for coating the active material, and the coating layer containing a tungsten element A constituent active coating material has been proposed (see, for example, Patent Document 1). LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the base material powder in the coating active material, and tungsten is used as the coating raw material as a means for forming a resistance reducing layer on the surface of the base material powder. A rolling flow coating method using a simple substance or a tungsten compound is adopted.

In addition, it suppresses gelation of the positive electrode mixture paste, can maintain the battery capacity when used in a secondary battery, has high output characteristics, and has excellent charge / discharge cycle characteristics. The positive electrode active material for a battery is composed of a lithium metal composite oxide powder having a layered crystal structure, and the lithium metal composite oxide powder has the formula: Li _s Ni _1-xyz Co _x M n _y M _z O _{2 + α} ( In the formula, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 1.00 <s <1.30, 0 ≦ α ≦ 0.2, M is V , Mg, Mo, Nb, Ti, W and Al), a second element containing lithium and secondary particles formed by aggregation of primary particles. At least selected from the group consisting of a compound and the second compound present on the surface of the primary particle and consisting of a lithium-free oxide, a hydrate of the oxide and a lithium-free inorganic acid salt. One kind of the first compound is a compound produced by reacting with lithium ions in the presence of water, and the pH of the supernatant liquid after 5 g of the positive electrode active material is dispersed in 100 mL of pure water and allowed to stand for 10 minutes. A positive electrode active material for a non-aqueous electrolyte secondary battery in which the temperature is 11 to 11.9 at a temperature of 25 ° C. has been proposed (see, for example, Patent Document 2).

Further, in an all-solid-state battery, as a means for suppressing the reaction between the sulfide-based solid electrolyte and LiCoO ₂ and reducing the interfacial resistance, a sol-gel method is used in which a metal alkoxide is used as a coating material on the surface of LiCoO ₂ particles of the base metal powder. A method of coating a compound such as Li ₂ SiO ₃ , LiNbO ₃ , and LiTaO ₃ using Li ₂ SiO ₃ has been proposed (see, for example, Non-Patent Documents 1 to 3).

However, in the inventions described in Patent Documents 1 and 2 and Non-Patent Documents 1 to 3, a surplus lithium compound such as lithium hydroxide is contained on the particle surface of the lithium metal composite oxide constituting the base material powder. Therefore, when a positive electrode mixture paste is prepared using the lithium metal composite oxide, the lithium compound may be eluted into the solvent contained in the positive electrode mixture paste, and the positive electrode mixture paste may gel.

Further, as described in Patent Document 1 and Non-Patent Documents 1 to 3, as a method for forming a resistance reducing layer on the particle surface of the base metal powder, a rolling fluid coating in which a tungsten simple substance or a tungsten compound is used as a coating raw material. When the method or the sol-gel method in which a metal alkoxide is used as a coating raw material is adopted, the raw material cost and the cost required for the coating process are high, so that it is not possible to industrially manufacture a lithium ion secondary battery.

In the inventions described in Patent Documents 1 and 2, when the surplus lithium compound is used as the lithium source of the coating compound, the amount of the coating raw material added such as the tungsten compound and the molybdenum compound is relative to the amount of the lithium compound. When the amount is small, the obtained positive mixture paste gels, and when the amount of the coating raw material added is relatively large with respect to the amount of the lithium compound, the base material powder constituting the composite oxide together with nickel, cobalt, etc. Since even lithium required for itself is deprived, there is a risk that the performance as a positive electrode active material will not be fully exhibited.

Further, in the invention described in Patent Document 2, when determining the addition amount of a compound such as a tungsten compound or a molybdenum compound as a coating raw material, a small amount of the base metal powder and the coating raw material are used in advance to test the positive electrode activity. A lithium ion secondary battery requires a complicated preliminary experiment of producing a substance and confirming the amount of the compound required to keep the pH of the slurry of the positive electrode active material within a predetermined range. Cannot be produced industrially and efficiently.

International Publication No. 2012/1005048 International Publication No. 2017/073238

Chemistry of Materials, Vol. 22, 2010, pp. 949-956 Electrochemistry Communications, Vol. 9, 2007, pp. 1486-1490 Solid State Ionics, Vol. 179, 2008, pp. 1333-1337

The present invention has been made in view of the above-mentioned prior art, and is a positive electrode active material for a lithium ion secondary battery having a low positive electrode resistance and a high retention rate of discharge capacity when used in a lithium ion secondary battery, and production thereof. It is an object of the present invention to provide a method and a lithium ion secondary battery having a positive electrode containing the positive electrode active material for the lithium ion secondary battery.

The present invention
(1) A positive electrode active material for a lithium ion secondary battery, wherein a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide containing lithium, nickel and cobalt are aggregated is used as a raw material. A coating layer containing at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate is formed on the surface of the secondary particles, and the average thickness of the coating layer is 3 to 150 nm. , A positive electrode active material for a lithium ion secondary battery, characterized in that the fluctuation index (CV%) indicating the variation in the thickness of the coating layer is 15% or less.
(2) The lithium ion secondary battery according to (1) above, wherein the content of lithium hydroxide in the positive electrode active material is less than 0.003% by mass and the content of lithium carbonate is less than 0.003% by mass. Positive electrode active material,
(3) The lithium metal composite oxide has the formula (I):
_{Li s Ni 1-xy Co x} M y O 2 + α (I)
(In the formula, s, x, y and α are 1.00 ≦ s ≦ 1.30, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.45 and −0.1 ≦ α ≦ 0, respectively. A number satisfying .2, M represents at least one metal element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, W and Al).
The positive electrode active material for a lithium ion secondary battery according to (1) or (2) above, which is a lithium metal composite oxide represented by.
(4) The positive electrode active material for a lithium ion secondary battery is a positive electrode active material for a non-aqueous electrolyte lithium ion secondary battery or a positive electrode active material for a lithium ion secondary battery for an all-solid-state battery (1) to (3) above. The positive electrode active material for a lithium ion secondary battery according to any one,
(5) A lithium ion secondary battery having a positive electrode containing the positive electrode active material for the lithium ion secondary battery according to any one of (1) to (4) above, and (6) lithium as a raw material. , A method for producing a positive electrode active material for a lithium ion secondary battery using a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide containing nickel and cobalt are aggregated. The first mixture was prepared by mixing the base metal powder and water so that the content of water in the mixture of the powder and water was 4 to 7% by mass, and the temperature of the first mixture obtained above was adjusted. The temperature is adjusted to 25 to 50 ° C., the first mixture is mixed with the coating raw material to prepare a second mixture, and the second mixture obtained above is dried at a temperature of 150 to 250 ° C. to obtain a base material powder. At least one compound selected from the group consisting of a tungsten compound and a molybdenum compound as the coating raw material, which comprises a step of producing a positive electrode active material by forming a coating layer on the surface of the secondary particles contained in the above. The total amount of tungsten and molybdenum contained in the coating material for lithium of the surplus lithium compound contained in the base material powder is adjusted to 0.8 to 1.2 equivalents using the coating material containing. The lithium ion compound according to any one of (1) to (4) above, wherein the total amount of tungsten and molybdenum per 100 parts by mass of the base material powder is adjusted to 0.1 to 6 parts by mass. The present invention relates to a method for producing a positive electrode active material for a next battery.

According to the present invention, a positive electrode active material for a lithium ion secondary battery having a low positive electrode resistance and a high retention rate of discharge capacity when used in a lithium ion secondary battery, a method for producing the same, and the lithium ion secondary battery. A lithium ion secondary battery having a positive electrode containing a positive electrode active material is provided.

It is a schematic explanatory drawing which shows one Embodiment of the positive electrode active material for a lithium ion secondary battery of this invention.

Hereinafter, the positive electrode active material for a lithium ion secondary battery of the present invention, a method for producing the same, and a lithium ion secondary battery having a positive electrode containing the positive electrode active material for the lithium ion secondary battery will be described in detail. The present invention is not limited to the embodiments described below, and the embodiments can be modified based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

1. 1. Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for lithium ion secondary battery of the present invention is, as described above, secondary particles in which primary particles of a lithium metal composite oxide containing lithium, nickel and cobalt are aggregated. It is a positive electrode active material for a lithium ion secondary battery in which a base metal powder containing the above is used as a raw material.

In the positive electrode active material for a lithium ion secondary battery of the present invention, a coating layer containing at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate is formed on the surface of the secondary particles. One of the features of the present invention is that the average thickness of the coating layer is 3 to 150 μm, and the coefficient of variation (CV%) indicating the variation in the thickness of the coating layer is 15% or less. Since the positive electrode active material for a lithium ion secondary battery of the present invention has the above-mentioned constituent requirements, it has excellent effects of low positive electrode resistance and high discharge capacity retention rate when used in a lithium ion secondary battery. ..

As a raw material for the positive electrode active material for a lithium ion secondary battery, a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide containing lithium, nickel and cobalt are aggregated can be used.

(1) Base material powder The method for preparing the base material powder will be described below, but the present invention is not limited to the preparation method. The base metal powder contains secondary particles in which primary particles of lithium metal composite oxide are aggregated. The base metal powder may inevitably contain a small amount of primary particles of the lithium metal composite oxide.

Lithium compound particles, nickel compound particles, cobalt compound particles and, if necessary, added metal M particles can be used as raw materials for the secondary particles of the lithium metal composite oxide constituting the base metal powder.

(A) Preparation of metal composite hydroxide (precursor) particles [crystallization]
First, as a raw material solution, an aqueous solution of a metal compound containing nickel, cobalt and, if necessary, an additive metal M such as manganese or aluminum is prepared. An aqueous solution of a metal compound can be easily prepared, for example, by dissolving the metal compound in water having a water temperature of about 30 ° C. As the water, pure water such as ion-exchanged water is preferable. The water temperature of the aqueous solution of the metal compound is preferably about 30 ° C.

Examples of the metal compound include metal sulfates, metal aluminates, metal hydrates, and the like, but the present invention is not limited to these examples. Each of these metal compounds may be used alone, or two or more kinds may be used in combination. Any of these compounds can be suitably used in the present invention.

The concentration of the metal compound in the aqueous solution of the metal compound is not particularly limited, but is usually 1.0 to 2.6 mol / L.

Then added an aqueous solution of the metal compound in water at 40 to 60 ° C., by adjusting the pH and ammonium ions (NH ₄ ⁺⁾ concentration as will be described later, to crystallize the particles. When the particles are crystallized, the formation of secondary particles by agglutination of primary particles proceeds in parallel.

The temperature of the water is preferably 40 ° C. or higher from the viewpoint of suppressing the coarsening of the metal composite hydroxide particles, and 60 ° C. or lower from the viewpoint of suppressing the miniaturization of the metal composite hydroxide particles. preferable. As the water, pure water such as ion-exchanged water is preferable.

When an aqueous solution of the metal compound is added to water at 40 to 60 ° C., it is preferable to use a reaction vessel. When a reaction tank is used, an aqueous solution of the metal compound is added to water at 40 to 60 ° C. injected into the reaction tank. Hereinafter, the case where the reaction vessel is used will be described.

When an aqueous solution of the metal compound is added to water at 40 to 60 ° C., it is preferable to stir the water from the viewpoint of efficiently crystallizing the particles.

When crystallizing the particles, if the particles have a "solid" particle structure, for example, an inert gas such as nitrogen gas is introduced from the upper part of the reaction tank, and the inside of the reaction tank is introduced. It is preferable to adjust the atmosphere so that the oxygen concentration is 1% by volume or less, which is a non-oxidizing atmosphere.

When the particles have a "hollow" or "porous" particle structure, for example, the atmosphere in the reaction vessel is adjusted to an oxidizing atmosphere such as air, and the pH of an aqueous sodium hydroxide solution or the like is adjusted. while adjusting the pH of water in the reaction vessel to 11.0 to 12.5 by adjusting agent, ammonia water to adjust the aqueous solution and ammonium ions (NH ₄ ⁺⁾ concentration of the metal compound to the reaction vessel It is preferable to add it. The pH of the water is preferably 11.0 or more from the viewpoint of reducing the concentration of sulfate remaining in the positive electrode active material and improving the output characteristics of the battery, and the metal composite hydroxide particles become too small. It is preferably 12.5 or less from the viewpoint of suppressing. The concentration of ammonium in the contents of the reaction vessel ions (NH ₄ ^+), from the viewpoint of stabilizing the crystallization process, preferably 5 to 30 g / L, more preferably 10 to 20 g / L.

After crystallization of the particles, the treatment is subsequently carried out under the following conditions so that the particles have a particle structure of any one of "solid", "hollow" and "porous".

When the particles have a "solid" particle structure, for example, it is preferable to continue the crystallization treatment for growing the particles while maintaining the inside of the reaction vessel in a non-oxidizing atmosphere. .. When the particles had a "hollow" particle structure, the addition of the aqueous solution of the metal compound and aqueous ammonia was stopped, and the atmosphere in the reaction vessel was changed from an oxidizing atmosphere to a non-oxidizing atmosphere. After that, it is preferable to restart the addition of the aqueous solution of the metal compound and the aqueous ammonia solution and continue the crystallization treatment for growing the particles. When the particles have a "porous" particle structure, for example, the addition of the aqueous solution of the metal compound and aqueous ammonia is stopped, and the atmosphere in the reaction vessel is changed from an oxidizing atmosphere to a non-oxidizing atmosphere. By changing, the addition of the aqueous solution of the metal compound and the aqueous ammonia is restarted, the non-oxidizing atmosphere is changed to the oxidizing atmosphere, and the series of operations of changing from the oxidizing atmosphere to the non-oxidizing atmosphere is performed a plurality of times. It is preferable to continue the crystallization treatment for growing the particles.

As described above, by controlling the atmosphere in the reaction vessel to a non-oxidizing atmosphere or an oxidizing atmosphere, the metal composite hydroxide can be adjusted to have a predetermined particle structure.

Here, by controlling the temperature in the reaction vessel to 40 to 60 ° C., the particle size of the metal composite hydroxide can be adjusted to a preferable size. Further, by controlling the pH of the water to 11.0 to 12.5, it is possible to reduce the sulfate and adjust the particle size in the subsequent step. Also, preferably the ammonium ion (NH ₄ ⁺⁾ concentration 5 to 30 g / L, more preferably by controlling the 10 to 20 g / L, it is possible to stabilize the crystallization process.

By performing the above operation, metal composite hydroxide (precursor) particles can be obtained. The void ratio of the metal composite hydroxide particles is determined when the particle structure of the metal composite hydroxide particles is "solid" from the viewpoint of improving the particle strength and the contact area with the electrolytic solution. It is preferably 20% or less, more preferably 5% or less, and preferably 10 to 90%, more preferably 20 to 50% when the particle structure of the metal composite hydroxide particles is “hollow”. When the particle structure of the metal composite hydroxide particles is "porous", it is preferably 40 to 90%, more preferably 50 to 80%.

[Filtration / drying]
The crystallized product of the metal composite hydroxide particles obtained above is solid-liquid separated by a filtration device such as a filter press filter, and the recovered solid metal composite hydroxide particles are washed with washing water. Thereby, impurities can be removed from the metal composite hydroxide particles.

Since moisture adheres to the surface of the water-washed metal composite hydroxide particles, it is preferable to dry the metal composite hydroxide particles with a dryer. Examples of the dryer include a static dryer, a fluid dryer, and an airflow dryer, but the present invention is not limited to these examples. When a heating type dryer is used as the dryer, it is preferable that the heating type dryer is an electric heating type dryer that does not generate carbon gas in a drying atmosphere.

The drying temperature of the metal composite hydroxide particles is preferably 100 ° C. or higher, more preferably 120 ° C. or higher from the viewpoint of increasing the drying efficiency, and preferably 200 ° C. from the viewpoint of suppressing deterioration of the metal composite hydroxide particles. ° C or lower, more preferably 180 ° C or lower. Since the drying time of the metal composite hydroxide particles varies depending on the drying temperature of the metal composite hydroxide particles and the like, it cannot be unconditionally determined. Therefore, it depends on the drying temperature of the metal composite hydroxide particles and the like. It is preferable to determine it as appropriate, but it is usually about 1 to 5 hours.

The average particle size of the metal composite hydroxide particles is preferably 3 μm or more, more preferably 4 μm or more, and the ratio of the positive electrode active material, from the viewpoint of increasing the battery capacity by increasing the packing density of the metal composite hydroxide particles. From the viewpoint of increasing the surface area and improving the output characteristics of the battery, it is preferably 20 μm or less, more preferably 15 μm or less. The average particle size of the metal composite hydroxide particles is obtained from the volume reference distribution measured using a laser diffraction / scattering type particle size distribution measuring device [Microtrack Bell Co., Ltd., trade name: Microtrack MT3300EXII]. Be done.

The composition of the metal composite hydroxide particles can be analyzed by a chemical analysis method such as acid decomposition-ICP (inductively coupled plasma) emission spectroscopy.

(B) Preparation of metal composite oxide (intermediate) particles [oxidative roasting]
By oxidatively roasting the metal composite hydroxide particles obtained above in an oxygen-containing atmosphere such as air, metal composite oxide particles that are oxidatively roasted products can be obtained.

When oxidatively roasting the metal composite hydroxide particles, for example, a heating furnace such as a high temperature heating furnace can be used. The heating furnace may be either a batch type heating furnace or a continuous type heating furnace. Among the heating furnaces, an electric furnace is preferable because there is no possibility of generating combustion gas.

The temperature at which the metal composite hydroxide particles are oxidatively roasted is preferably 800 to 1000 ° C. from the viewpoint of improving the mechanical strength of the metal composite oxide particles and preventing sintering of the metal composite oxide particles. More preferably, it is 800 to 900 ° C. The time required for oxidative roasting of the metal composite hydroxide particles varies depending on the temperature at which the metal composite hydroxide particles are oxidatively roasted, and therefore cannot be unconditionally determined. It is preferable to appropriately determine the oxide particles according to the temperature at which the oxide particles are oxidatively roasted, but it is usually about 1 to 5 hours.

Before oxidatively roasting the metal composite hydroxide particles, the metal composite hydroxide water is sufficiently removed from the metal composite hydroxide particles to improve the mechanical strength of the metal composite hydroxide particles. Oxide particles may be calcined. The calcining of the metal composite hydroxide particles can be carried out, for example, by heating the metal composite hydroxide particles at a temperature of 400 to 550 ° C., preferably 450 to 500 ° C. for about 1 to 3 hours.

The average particle size of the metal composite oxide particles is preferably 3 μm or more, more preferably 4 μm or more, and the specific surface area of the positive electrode active material is increased from the viewpoint of increasing the battery capacity by increasing the packing density of the metal composite oxide particles. From the viewpoint of increasing and improving the output characteristics of the battery, it is preferably 20 μm or less, more preferably 15 μm or less. The average particle size of the metal composite oxide particles is obtained from the volume reference distribution measured using a laser diffraction / scattering type particle size distribution measuring device [Microtrack Bell Co., Ltd., trade name: Microtrack MT3300EXII]. ..

The composition of the metal composite oxide particles can be analyzed by a chemical analysis method such as acid decomposition-ICP (inductively coupled plasma) emission spectroscopy.

(C) Preparation of base material powder The metal composite oxide particles and lithium compound particles are used as raw materials for the base material powder.

[Lithium compound particles]
Examples of the lithium compound constituting the lithium compound particles include lithium carbonate (Li ₂ CO ₃ , melting point: 723 ° C.), lithium hydroxide (LiOH, melting point: 462 ° C.), lithium nitrate (LiNO ₃ , melting point: 261 ° C.). , Lithium chloride (LiCl, melting point: 613 ° C.), lithium sulfate (Li ₂ SO ₄ , melting point: 859 ° C.) and the like, but the present invention is not limited to these examples. Each of these lithium compounds may be used alone, or two or more kinds may be used in combination. Among these lithium compounds, lithium hydroxide and lithium carbonate are preferable because they are easy to handle and their quality is stable.

The maximum particle size of the lithium compound particles is preferably 10 μm or less, and the average particle size of the lithium compound particles is preferably 5 μm or less. The maximum particle size of the lithium compound particles is such that the average particle size is measured using a laser diffraction / scattering type particle size distribution measuring device [Microtrack Bell Co., Ltd., trade name: Microtrack MT3300EXII]. The average particle size of is obtained from the volume reference distribution measured using the measuring device.

[Preparation of lithium mixture]
A lithium mixture is obtained by mixing the metal composite oxide particles and the lithium compound particles.

The metal composite oxide particles and the lithium compound particles are values of the ratio of the total number of atomic elements of metal elements contained in the lithium metal composite oxide to the number of lithium atoms (hereinafter, simply "ratio value"). It is preferable to mix so that () is 1.0 to 1.2. The upper limit of the value of the ratio is preferably 1.2 or less from the viewpoint of suppressing coarsening of the particle diameter and crystallite diameter and improving the cycle characteristics. When the metal composite oxide and the lithium compound are mixed at the above ratio value, lithium atoms are incorporated into 3a sites, which are lithium sites, so that the battery characteristics can be improved. The site means a crystallographically equivalent lattice position. The presence of atoms at the lattice position is called "site occupied", and the occupied site is called "occupied site". Taking LiCoO ₂ as an example, there are three occupied sites in the LiCoO ₂ . The three occupied sites are referred to as lithium sites, cobalt sites and oxygen sites, respectively, and 3a sites, 3b sites and 6c sites, respectively.

[Preparation of base metal powder]
By firing the lithium mixture in an oxidizing atmosphere such as air, a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide are aggregated can be obtained. The oxygen concentration in the oxidizing atmosphere is preferably 18 to 100% by volume.

The firing temperature of the lithium mixture is preferably 800 ° C. or higher, more preferably 900 ° C. or higher, and among the particles of the lithium metal composite oxide, from the viewpoint of reducing the amount of unreacted lithium compound and improving the crystallinity. From the viewpoint of suppressing excessive progress of sintering, the temperature is preferably 1000 ° C. or lower. Since the calcination time of the lithium mixture varies depending on the calcination temperature of the lithium mixture and the like, it cannot be unconditionally determined. Therefore, it is preferable to appropriately determine the calcination time according to the calcination temperature of the lithium mixture, but usually, 1 is preferable. It is about 20 hours, more preferably about 10 to 15 hours.

Before firing the lithium mixture, the reaction during firing of the lithium mixture is gently promoted to improve the mechanical strength of the fired product, reduce the amount of unreacted lithium compounds, and improve the crystallinity. From the viewpoint, the lithium mixture may be calcined in an oxygen-containing atmosphere such as air. The calcining of the lithium mixture can be carried out, for example, by heating the lithium mixture at a temperature of 400 to 550 ° C, preferably 450 to 500 ° C for about 1 to 3 hours. The oxygen concentration in the oxygen-containing atmosphere is preferably 18 to 100% by volume.

By firing the lithium mixture as described above, primary particles of the lithium metal composite oxide are formed from the metal composite oxide particles and the lithium compound particles, and the primary particles of the lithium metal composite oxide are aggregated. A base metal powder containing the secondary particles is obtained. The secondary particles usually have a spherical or elliptical spherical shape, but may contain irregular particles.

The particle size of the primary particles of the lithium metal composite oxide is not particularly limited, but is usually about 0.2 to 1 μm. The particle size of the secondary particles is usually about 3 to 30 μm. The particle diameters of the primary particles and the secondary particles are based on the volume reference distribution measured using a laser diffraction / scattering type particle size distribution measuring device [Microtrack Bell Co., Ltd., trade name: Microtrack MT3300EXII]. Desired.

The base material powder is essentially composed of the secondary particles, but the primary particles may inevitably be contained in a small amount in addition to the secondary particles.

In the present invention, the base material powder obtained above can be used as a raw material for the positive electrode active material for a lithium ion secondary battery, but a commercially available base material powder may also be used. Among the commercially available base material powders, those in which the slurry prepared by using the base material powder exhibits a predetermined pH can be used as the base material powder. The pH of the base material powder slurry will be described later.

By the way, since the average thickness of the coating layer formed on the surface of the positive electrode active material of the present invention is as thin as 3 to 150 nm as described later, the positive electrode active material of the present invention is the average of the base metal powder. It inherits powder characteristics and particle structure such as particle size MV, particle size distribution, and tap density (bulk density). Therefore, by selecting the powder characteristics and the particle structure of the base material powder, the properties of the base material powder can be imparted to the positive electrode active material.

[Composition of Lithium Metal Composite Oxide]
As described above, the base metal powder is substantially composed of the secondary particles, but the primary particles may inevitably be contained in a small amount in addition to the secondary particles. Both the primary particles and the secondary particles are composed of a lithium metal composite oxide.

From the viewpoint of obtaining a positive electrode active material for a lithium ion secondary battery, which has a low positive electrode resistance and a high retention rate of discharge capacity when the lithium metal composite oxide is used in a lithium ion secondary battery, the formula (I):
_{Li s Ni 1-xy Co x} M y O 2 + α (I)
(In the formula, s, x, y and α are 1.00 ≦ s ≦ 1.30, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.45 and −0.1 ≦ α ≦ 0, respectively. A number satisfying .2, M represents at least one metal element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, W and Al).
It is preferably a lithium metal composite oxide represented by.

The composition of the base metal powder is, for example, mixing the base metal powder and the inorganic acid (35% hydrochloric acid) in appropriate amounts, heat-decomposing the obtained mixture, and adding an appropriate amount of pure to the obtained decomposition liquid. An analytical sample solution is prepared by adding water, and the analytical sample solution is specified by spectroscopic analysis with a multi-type ICP emission spectroscopic analyzer [manufactured by Shimadzu Corporation, product number: ICPE-9000]. Can be done.

[PH of base powder slurry]
Since the surplus lithium compound contained in the base metal powder is mainly composed of lithium hydroxide, there is a difference between the content of the surplus lithium compound in the base material powder and the pH of the slurry of the base material powder. There is a strong correlation. Therefore, by measuring the pH of the slurry of the base material powder, the content of the excess lithium compound in the base material powder can be specified more quickly and easily than in the conventional titration method.

The base material powder slurry can be prepared by mixing the base material powder and pure water at a ratio of 95 mL of pure water to 5 g of the base material powder and dispersing the base material powder in pure water. The pH of the base material powder slurry is preferably 10.5 from the viewpoint of controlling the content of excess lithium compounds contained in the base material powder to the optimum content of 0.045 to 1.6% by mass. It is ~ 12.5, more preferably 11.0 to 12.5, even more preferably 11.0 to 12.2, and even more preferably 11.6 to 12.2.

For the pH of the base metal powder slurry, after allowing the base material powder slurry to stand for 10 minutes, the pH of the supernatant is measured by a pH meter [manufactured by Thermo Fisher Scientific Co., Ltd., trade name: Orion-star-A214 (trade name: Orion-star-A214). It is a value when measured by (desktop type) or trade name: Orion-star-A221 (handy type)].

[Average particle size MV and particle size distribution of base material powder]
The particle size distribution [(d90-d10) / average particle size MV], which is an index showing the spread of the particle size distribution of the base material powder, enhances the filling property of the positive electrode active material and the battery capacity per battery volume, and constitutes the positive electrode active material. It is preferably 1.0 or less from the viewpoint of equalizing the applied voltage between the secondary particles and enhancing the cycle characteristics by equalizing the load between the secondary particles.

In the particle size distribution [(d90-d10) / average particle size MV], which is an index indicating the spread of the particle size distribution, d10 accumulates the number of particles of particles having each particle size from the smaller particle size side, and the accumulation thereof. It means the particle size when the volume is 10% of the total volume of all particles. Similar to d10, d90 means the particle diameter when the number of particles having each particle diameter is accumulated from the smaller particle diameter side and the accumulated volume is 90% of the total volume of all particles.

The average particle size MV and particle size distribution [(d90-d10) / average particle size MV] of the base metal powder are a laser diffraction / scattering type particle size distribution measuring device [manufactured by Microtrack Bell Co., Ltd., trade name: Microtrack]. It is obtained from the volume-based distribution of the base material powder measured using MT3300EXII].

As with d10 and d90, a particle diameter having a cumulative volume of 50% of the total particle volume, in other words, d50 having a median diameter, may be used instead of the average particle diameter MV.

[Tap density (bulk density) of base metal powder]
The tap density of the base metal powder is preferably 1.0 / cm ³ or more, more preferably 1.8 / cm, from the viewpoint of reducing the voids when the electrodes of the lithium ion secondary battery are manufactured and improving the battery performance. ³ or more, more preferably 2.0 / cm ³ or more. In addition, the tap density of the base metal powder improves the contact area between the positive electrode active material and the electrolytic solution when the positive electrode active material is used in a non-aqueous electrolyte lithium ion secondary battery, and the positive electrode active material is an all-solid lithium ion secondary battery. When used in a secondary battery, a solid electrolyte is introduced between the particles of the positive electrode active material to reduce the electrical resistance of the lithium ion secondary battery and increase the battery capacity, preferably 3.0 / cm ³ or less. It is preferably 2.4 / cm ³ or less, and more preferably 2.2 / cm ³ or less.

For the tap density of the base metal powder, 12 g of the base metal powder was filled in a 20 mL graduated cylinder, and the graduated cylinder was attached to a shaking specific gravity measuring instrument [manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd., product number: KRS-409]. This is the density of the base metal powder measured after the base material powder is densely filled by repeating the operation of freely dropping the graduated cylinder from a height of 2 cm 500 times.

(2) First Mixture The first mixture can be obtained by mixing the base metal powder and water so that the content of water in the mixture of the base material powder and water is 4 to 7% by mass.

The content of water in the mixture of the base material powder and water is 4 from the viewpoint of allowing water to sufficiently penetrate into the voids and grain boundaries between the primary particles constituting the secondary particles contained in the base material powder. By mass% or more, preferably 5% by mass or more, the drying efficiency in the drying step which is a subsequent step is increased, the amount of lithium eluted from the base material powder is reduced, and the battery of the battery in which the positive electrode active material is used for the positive electrode. From the viewpoint of improving the characteristics, it is 7% by mass or less, preferably 6% by mass or less.

The atmosphere and temperature at which the base metal powder and water are mixed are not particularly limited. The atmosphere when the base metal powder and water are mixed may be air, or may be, for example, an inert gas such as nitrogen gas or argon gas. The temperature at which the base metal powder and water are mixed can be appropriately determined from a temperature range of 5 to 95 ° C., preferably a temperature range of 10 to 80 ° C., but from the viewpoint of improving energy efficiency. , Usually preferably at room temperature.

The base metal powder and water can be mixed by using, for example, a mixer such as a shaker mixer, a stirring mixer, or a locking mixer. It is preferable that the base metal powder and water are mixed until both are uniformly dispersed and a mixture having a uniform composition is obtained.

(3) Second Mixture The second mixture can be prepared by adjusting the temperature of the first mixture obtained above to 25 to 50 ° C. and mixing the first mixture with the coating raw material.

In the present invention, when the first mixture and the coating raw material are mixed, a coating raw material containing at least one compound selected from the group consisting of a tungsten compound and a molybdenum compound is used as the coating raw material, and the base material is used. The total amount of tungsten and molybdenum contained in the coating raw material for the excess lithium compound contained in the powder is adjusted to 0.8 to 1.2 equivalents, and tungsten per 100 parts by mass of the base material powder is adjusted. The total amount of molybdenum and molybdenum is adjusted to 0.1 to 6 parts by mass.

In the present invention, since the above operation is adopted, it is possible to dissolve the lithium compound remaining on the surface of the base metal powder and improve the solubility of the coating raw material to be added in water, and by extension, the lithium ion secondary. It is possible to obtain a positive electrode active material for a lithium ion secondary battery having a low positive electrode resistance and a high discharge capacity retention rate when used in a battery.

As the coating raw material, a coating raw material containing at least one compound selected from the group consisting of a tungsten compound and a molybdenum compound is used. The tungsten compound and the molybdenum compound may be used alone or in combination. Among the tungsten compounds and molybdenum compounds, the tungsten compound is preferable because water is unlikely to be produced as a by-product when it reacts with the excess lithium compound.

Examples of the tungsten compound include tungsten oxide, tungstic acid, ammonium tungstate, and the like, but the present invention is not limited to these examples. Each of these tungsten compounds may be used alone, or two or more kinds may be used in combination. Among the tungsten compounds, tungsten oxide and tungstic acid are more preferable, and tungsten oxide is further preferable, because water is unlikely to be produced as a by-product when reacting with the excess lithium compound.

Examples of the molybdenum compound include molybdenum oxide, molybdic acid, ammonium molybdate, and the like, but the present invention is not limited to these examples. Each of these molybdenum compounds may be used alone, or two or more of them may be used in combination. Among the molybdenum compounds, molybdenum oxide and molybdic acid are preferable, and molybdenum oxide is more preferable, because water is unlikely to be produced as a by-product when reacting with the excess lithium compound.

Tungsten oxide and molybdenum oxide are preferable from the viewpoint of improving the output characteristics of the lithium ion secondary battery and increasing the battery capacity. Among tungsten oxide and molybdenum oxide, tungsten oxide is preferable from the viewpoint of improving the lithium ion conductivity of the coating compound and promoting the movement of lithium ions.

The coating raw material may contain a coating raw material other than the tungsten compound and the molybdenum compound as long as the object of the present invention is not impaired. Examples of the coating raw material other than the tungsten compound and the molybdenum compound include vanadium pentoxide, niobium oxide, tin dioxide, manganese oxide, ruthenium oxide, rhenium oxide, tantalum oxide, phosphorus oxide, and boron oxide. , It is not limited to such an example. Each of these coating raw materials may be used alone, or two or more kinds may be used in combination.

When, for example, an oxide such as tungsten oxide or molybdenum oxide or a coating material such as a hydrate of the oxide is used as the coating material, the coating material forms an oxoanion in the presence of water. The oxoanion reacts with the excess lithium of the lithium compound to produce salts such as lithium tungstenate and lithium molybdate as lithium salts of the oxoanion. When the positive electrode active material used in the coating raw material is used in the lithium ion secondary battery, the positive electrode resistance of the lithium ion secondary battery can be lowered and the maintenance rate of the discharge capacity can be increased.

Further, in the present invention, the total amount of tungsten and molybdenum contained in the coating raw material for lithium of the surplus lithium compound contained in the base material powder is 0.8 to 1.2 equivalents. By using the positive electrode active material in which the coating raw material is used in the lithium ion secondary battery, the positive electrode resistance of the lithium ion secondary battery can be lowered and the maintenance rate of the discharge capacity can be increased.

When the total amount of tungsten and molybdenum contained in the coating raw material is smaller than the amount of excess lithium compound contained in the base metal powder, the mixture of the first mixture and the coating raw material is a gel. If the amount of excess lithium compounds contained in the base metal powder is large compared to the amount of excess lithium compounds contained in the base material powder, the crystal lattice of the base material powder forming a composite oxide together with nickel, cobalt, etc. Even lithium required for culling and deintercalation is deprived, and there is a tendency that the performance as a positive electrode active material cannot be fully exhibited. Therefore, the total amount of tungsten and molybdenum contained in the coating raw material for the excess lithium compound contained in the base material powder with respect to lithium is such that the mixture of the first mixture and the coating raw material suppresses gelation. From the viewpoint of fully exerting the performance as a positive electrode active material, it is 0.8 to 1.2 equivalents, preferably 0.9 to 1.1 equivalents, and more preferably 0.95 to 1.05 equivalents.

In addition, the total amount of tungsten and molybdenum contained in the coating raw material for lithium of the surplus lithium compound contained in the base material powder is 1 equivalent, for example, the coating compound described later is ditungsic acid. In the case of dilithium (Li ₂ WO ₄ ), it means the amount of reaction of 1 mol of tungsten atom (atomic weight: 183.85) with 2 mol of lithium atom (atomic weight: 6.941), and the coating compound is dimolybdic acid. In the case of dilithium (Li ₂ MoO ₄ ), it means the amount of reaction of 1 mol of molybdenum atom (atomic weight: 95.94) with 2 mol of lithium atom (atomic weight: 6.941). For example, in pure lithium tungsten (Li ₂ WO ₄ ) and lithium molybdate (Li ₂ MoO ₄ ), the composition ratio of lithium to tungsten (Li / W) and the composition ratio of lithium to molybdenum (Li / Mo). Are 2 respectively.

For example, as described above, when the coating compounds are Li ₂ WO ₄ and Li ₂ MoO ₄ , the equivalents of the coating compounds are of formula (II) :.
[Equivalent of coating compound]
= [Tungsten or molybdenum content (%) / Tungsten or molybdenum atomic weight] / [Lithium content (%) / (Lithium atomic weight x 2)] (II)
It is calculated based on.

When the coating compound is, for example, a compound such as Li ₄ WO ₅ , Li ₆ W ₂ O ₉ , Li ₄ Mo O ₅ , Li ₆ Mo ₂ O ₉ , what is the lithium atom, the tungsten atom, and the molybdenum atom, respectively? The equivalent amount of the coating compound can be obtained by modifying the formula (II) in consideration of whether or not it becomes mol.

The total amount of tungsten and molybdenum contained in the coating material per 100 parts by mass of the base metal powder is a lithium ion secondary battery having a low positive electrode resistance and a high discharge capacity retention rate when used in a lithium ion secondary battery. From the viewpoint of obtaining a positive electrode active material for a battery, the amount is 0.1 to 6 parts by mass.

The temperature of the first mixture when the first mixture and the coating raw material are mixed is a positive electrode active material for a lithium ion secondary battery, which has a low positive electrode resistance and a high discharge capacity retention rate when used in a lithium ion secondary battery. From the viewpoint of obtaining the above, the temperature is 25 ° C. or higher, preferably 30 ° C. or higher, more preferably 33 ° C. or higher, and when used in a lithium ion secondary battery, the positive electrode resistance is low and the retention rate of the discharge capacity is high. From the viewpoint of obtaining a positive electrode active material for a battery, the temperature is 50 ° C. or lower, preferably 45 ° C. or lower, more preferably 40 ° C. or lower, still more preferably 37 ° C. or lower.

The atmosphere and temperature at which the first mixture and the coating raw material are mixed are not particularly limited. The atmosphere when the first mixture and the coating raw material are mixed may be air, or may be, for example, an inert gas such as nitrogen gas or argon gas. The temperature at which the first mixture and the coating raw material are mixed can be appropriately determined from the range of preferably 5 to 95 ° C, more preferably 10 to 80 ° C, but is usually preferably room temperature. ..

The mixing of the first mixture and the coating raw material can be performed using, for example, a mixer such as a shaker mixer, a stirring mixer, or a locking mixer. It is preferable that the first mixture and the coating raw material are mixed until they are uniformly dispersed and have a uniform composition.

(4) Positive Electrode Active Material The positive electrode active material for a lithium ion secondary battery of the present invention is made from a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide containing lithium, nickel and cobalt are aggregated. A coating layer containing at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate is formed on the surface of the secondary particles, and the average thickness of the coating layer is formed. The thickness is 3 to 150 μm, and the fluctuation index (CV%) indicating the variation in the thickness of the coating layer is 15% or less. Since the positive electrode active material for a lithium ion secondary battery of the present invention has the above-mentioned configuration, a lithium ion secondary battery having a low positive electrode resistance and a high discharge capacity retention rate can be obtained by using the positive electrode active material. Can be done.

The positive electrode active material is prepared by drying the second mixture obtained above at a temperature of 150 to 250 ° C. to form a coating layer on the surface of secondary particles contained in the base material powder. be able to.

The drying temperature of the second mixture is 150 to 250 ° C., preferably 160 to 240 ° C., from the viewpoint of efficiently drying the second mixture and forming a coating layer having a uniform thickness with little variation in thickness. More preferably, it is 170 to 230 ° C.

Drying of the second mixture is performed from the viewpoint of avoiding the reaction between the carbon dioxide contained in the air and the coating layer, for example, an inert gas such as carbon dioxide-removed air, nitrogen gas, or argon gas. It is preferable to carry out in an atmosphere such as. The pressure of the atmosphere when drying the second mixture is preferably lower than atmospheric pressure from the viewpoint of increasing the drying efficiency of the second mixture. The drying of the second mixture is preferably carried out until almost no weight loss of the second mixture is observed. Since the drying time of the second mixture varies depending on the amount of the second mixture, the drying temperature and the like, it cannot be unconditionally determined. Therefore, it is preferable to appropriately determine the drying time according to the amount of the second mixture, the drying temperature and the like. However, it is usually about 1 to 24 hours.

When drying the second mixture, for example, a dryer such as a stationary dryer, a vibration dryer, a drum dryer, or a spray dryer can be used.

In the present invention, since the above-mentioned operation is adopted, the surface of the base metal powder has a preferable thickness, the thickness variation is small, and at least selected from the group consisting of lithium tungstate and lithium molybdate. A positive electrode active material containing secondary particles having a coating layer containing a high content of one type of lithium salt can be obtained. Further, since the lithium salt coating layer is provided on the surface of the secondary particles, the decrease in the specific surface area of the positive electrode active material is suppressed, and the lithium ion conduction path at the interface between the electrolytic solution and the solid electrolyte can be secured. Therefore, the battery capacity of the lithium ion secondary battery can be increased and the positive electrode resistance can be reduced.

As described above, a positive electrode active material containing secondary particles having a coating layer containing at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate on the surface can be obtained.

When a surplus lithium compound such as lithium hydroxide is mixed as an impurity in the coating compound constituting the coating layer, when a positive mixture paste for a non-aqueous electrolyte lithium ion secondary battery is prepared using a solvent, The lithium compound is eluted in the solvent, and as the pH of the solvent increases and the concentration of the lithium salt in the solvent increases, gelation is likely to occur, or a heterogeneous interface is formed in the all-solid lithium ion secondary battery. There is a risk of being solvent. Further, when the positive electrode active material mixed with the lithium compound is used for the positive electrode of the lithium ion secondary battery, the battery capacity and output characteristics are lowered. For these reasons, at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate having an excellent resistance reducing function is used as the coating compound.

The average particle size MV of the positive electrode active material increases the filling property of the positive electrode active material and the battery capacity per battery volume of the lithium ion secondary battery, and makes the applied voltage among the secondary particles constituting the positive electrode active material uniform. The thickness is preferably 5 to 15 μm from the viewpoint of uniforming the load between the secondary particles and enhancing the cycle characteristics. The average particle size MV of the positive electrode active material is obtained from the volume reference distribution measured by the laser diffraction / scattering method.

The tap density (bulk density) of the positive electrode active material improves the battery performance by reducing the voids when the electrodes of the lithium ion secondary battery are manufactured and increasing the contact points between the positive electrode active material and the electrolyte and the solid electrolyte. From the viewpoint of increasing, it is preferably 1.0 g / cm ³ or more, and when the positive electrode active material is used in a non-aqueous electrolyte lithium ion secondary battery, the contact area between the positive electrode active material and the electrolytic solution is improved, and the positive electrode active material is used. 3.0 g / g / from the viewpoint of sufficiently introducing a solid electrolyte between the particles of the positive electrode active material to reduce the electric resistance of the lithium ion secondary battery and increase the battery capacity when the above is used in the all-solid lithium ion secondary battery. It is preferably cm ³ or less.

When the positive electrode active material of the present invention is used as the positive electrode active material of a non-aqueous electrolyte lithium ion secondary battery, the intercalation and deintercalation of lithium ions between the electrolytic solution and the positive electrode active material become active, and the whole solid. In a lithium ion secondary battery, lithium ions diffuse at the interface between the solid electrolyte and the positive electrode active material without stagnation. Therefore, while maintaining the durability of the lithium ion secondary battery, the positive electrode resistance is reduced and the output characteristics are improved. Can be made to.

If the secondary particles are agglomerated, the secondary particles may be coagulated, if necessary, with a decoction machine such as a pin mill, a hammer mill, or a palvelizer. Further, the secondary particles may be decoagulated using a drum dryer capable of simultaneously drying the second mixture and decoagulating the agglutinated secondary particles.

When the coating layer formed on the surface of the secondary particles is lithium tungstate, the lithium tungstate may be, for example, Li ₂ WO ₄ , Li ₄ WO ₅ , Li ₆ W ₂ O ₉ or a mixture thereof. Can be mentioned. When the coating layer formed on the surface of the secondary particles is lithium molybdate, the lithium molybdate can be, for example, Li ₂ MoO ₄ , Li ₄ MoO ₅ , Li ₆ Mo ₂ O ₉ or a mixture thereof. Can be mentioned.

The coating layer may contain a lithium salt other than lithium tungstate and lithium molybdate as long as the object of the present invention is not impaired. Examples of lithium salts other than lithium tungstate and lithium molybdate include lithium vanadate, lithium niobate, lithium tinate, lithium manganate, lithium ruthenate, lithium reniumate, lithium tantalate, lithium borate, and boric acid. Examples thereof include lithium, but the present invention is not limited to such examples. Each of these lithium salts may be used alone, or two or more kinds may be used in combination.

[Analysis of positive electrode active material]
The positive electrode active material can be analyzed by the following method.
(A) Lithium hydroxide (LiOH) content and lithium carbonate (Li ₂ CO ₃ ) content in the positive electrode active material Lithium hydroxide (LiOH) content and lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material The content of the above is preferably less than 0.003% by mass from the viewpoint of obtaining a lithium ion secondary battery having a low positive electrode resistance and a high retention rate of the discharge capacity by using the positive electrode active material. The contents of lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are the values measured based on the following methods, respectively.

[Method for measuring the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material]
The content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material can be determined by the neutralization titration method, respectively.

More specifically, lithium hydroxide and lithium carbonate existing on the surface of the positive electrode active material particles become hydroxide ions and carbonate ions, respectively, and are ionized from the lithium ions by being dissolved in water. .. By titrating these ionized ions with an inorganic acid or the like, lithium hydroxide and lithium carbonate can be quantified, respectively. The neutralization titration method is based on the so-called R. B. It is a sequential titration method by the Warder method. In the neutralization titration method, the first end point (pH: about 8.3) is a pH change point when the total amount of lithium hydroxide and half the amount of lithium carbonate react, and the second end point (pH: about 8.3). 3.8) is the pH change point when the remaining half of lithium carbonate reacts. The inflection point (end point) of pH can be confirmed by visually observing the discoloration of the indicator using an indicator such as phenolphthalein or methyl orange, and the change in potential difference due to the pH composite electrode is instrumental. It can be confirmed by reading to.

More specifically, for example, 2 to 20 g of the positive electrode active material is collected, the positive electrode active material and 120 mL of pure water are mixed, and 1 mol / L hydrochloric acid is gradually added to the mixed mixture while stirring the obtained mixture. The content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material can be determined based on the two pH changes that appear after the addition. Further, when the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are determined by using a pH composite electrode, these contents are determined by, for example, an automatic titrator. It can be obtained based on the end point (potential difference) of the pH composite electrode using [manufactured by Hiranuma Sangyo Co., Ltd., product number: COM-1750].

The lower the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material, the more boron and base metal powder contained in the coating raw material. This supports the fact that the lithium compound, lithium, reacted at a value close to 1 equivalent.

(B) pH of slurry of positive electrode active material
The slurry of the positive electrode active material can be prepared by mixing the positive electrode active material and pure water at a ratio of 95 mL of pure water to 5 g of the positive electrode active material and dispersing the positive electrode active material in pure water. When the pH of the slurry is measured, it can be confirmed that the excess lithium compound does not remain excessively when the pH is 10 or less. The pH of the slurry of the positive electrode active material is a value measured based on the following method.

[Method for measuring pH of slurry of positive electrode active material]
For the pH of the slurry of the positive electrode active material, after allowing the slurry of the positive electrode active material to stand for 10 minutes, the pH of the supernatant is measured by a pH meter [manufactured by Thermo Fisher Scientific Co., Ltd., trade name: Orion-star- It is obtained by measuring with A214 (desktop type)].

(C) Identification of coating compound The coating compound constituting the coating layer existing on the surface of the secondary particles used in the positive electrode active material is identified by the synchrotron radiation powder X-ray diffraction method (SXRD) described later. However, it is preferable to identify by the synchrotron radiation powder X-ray diffraction method (SXRD) using "Spring-8" of the Synchrotron Radiation Research Center (National Research and Development Corporation RIKEN). The principle and phenomenon of the synchrotron radiation powder X-ray diffraction method (SXRD) are almost the same as those of the general X-ray diffraction method (XRD), and the X-ray wavelength is based on Bragg's law. Atomic arrangement and structural analysis can be performed from information such as the distance between crystal planes and the relationship between crystal planes and the angle formed by X-rays.

By using the synchrotron radiation powder X-ray diffraction method (SXRD), the type, structure and properties of trace substances can be analyzed in detail and accurately by taking advantage of the higher X-ray intensity and short pulse property than the X-ray diffraction method (XRD). be able to. Therefore, by using the synchrotron radiation powder X-ray diffraction method (SXRD), detailed structural analysis of a sample whose background noise is high and it is difficult to identify the target compound by the X-ray diffraction method (XRD) is performed. be able to. Therefore, in the synchrotron radiation powder X-ray diffraction method (SXRD), the coating layer having a thickness of nanometers existing on the surface of the secondary particles used in the positive electrode active material of the present invention is a pure lithium salt. It can be suitably used to confirm that it is configured.

(D) Average thickness of coating layer and coefficient of variation CV%
The average thickness of the coating layer formed on the surface of the secondary particles is the positive electrode active material for lithium ion secondary batteries, which has low positive electrode resistance and high discharge capacity retention rate when used in lithium ion secondary batteries. From the viewpoint of obtaining the above, it is 3 to 150 nm, preferably 4 to 120 nm. The average thickness of the coating layer is a value measured based on the following method.

The coefficient of variation CV% indicates the variation in the thickness of the coating layer. The coefficient of variation CV% is 15% or less from the viewpoint of stabilizing the intercalation and deintercalation of lithium ions and improving the lithium ion conductivity. The coefficient of variation CV% can be adjusted to 15% or less, for example, by controlling the thickness of the coating layer to a predetermined value. The coefficient of variation CV% is a value measured based on the following method.

[Measurement method of average thickness of coating layer and coefficient of variation CV%]
When a transmission electron microscope (TEM) observes a positive electrode active material using the transmission electron microscope, an image of diffraction contrast (scattering contrast) such as an interface between primary particles can be obtained. Therefore, a crystal of the positive electrode active material is mainly used. Suitable for sex analysis. On the other hand, the scanning transmission electron microscope (STEM) is a HAADF-STEM (High-angle-Annalar) based on Z (atomic number) contrast such as confirmation of a laminated structure in a compound and a semiconductor by using the scanning transmission electron microscope. -Dark-Field-Scanning-TEM) images are obtained, which is suitable for analysis of the composition of laminated structures in compounds and semiconductors. According to the scanning transmission electron microscope (STEM), an image reflecting the composition information can be obtained. Therefore, it is formed on the surface of the base metal powder containing nickel and cobalt like the positive electrode active material of the present invention. The thickness of the coating layer in nanometer units can be confirmed accurately.

After the positive electrode active material is dried, the secondary particles contained in the positive electrode active material are processed using a cross-section polisher (CP) [manufactured by JEOL Ltd., product number: SM-09010]. , A cross-section sample of the secondary particle is prepared, and the cross-section of the cross-section sample is observed with a scanning transmission electron microscope (STEM) [manufactured by JEOL Ltd., product number: ARM200F]. Draw two straight lines orthogonal to each other at the substantially center of the observation image of the cross section of the cross-sectional sample, measure the thickness of the coating layer at four points intersecting the two straight lines, and measure the thickness of 10 secondary particles (n). From = 40), the coefficient of variation CV% indicating the variation in the average thickness of the coating layer and the thickness of the coating layer is obtained.

(E) Constituent elements (equivalent and composition ratio) of the coating compound
In order to accurately identify the constituent elements of the coating compound identified by the synchrotron radiation powder X-ray diffraction method (SXRD) and their morphology, it is preferable to perform a chemical analysis together with an analysis of the physical properties of the coating compound.

The coating compound contains a water-soluble compound such as at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate. The constituent elements of the coating compound can be analyzed by utilizing the water solubility of the coating compound, and the total amount (equivalent) of tungsten and molybdenum can be determined based on the formula (II). Further, whether or not the type and morphology of each constituent element in the coating compound identified by the synchrotron radiation powder X-ray diffraction method (SXRD) is appropriate can be confirmed by the following analysis method of the constituent elements of the coating compound.

[Analysis method of constituent elements of coating compound]
A slurry is prepared by dispersing 5 g of the positive electrode active material in 95 mL of pure water at 25 ° C., the slurry is stirred for 10 minutes, filtered, and pure water is added to the filtrate so that the total volume becomes 200 mL. An analytical sample solution is prepared, the analytical sample solution is appropriately diluted, and the content of lithium, tungsten, and molybdenum contained in the analytical sample solution is determined by a multi-type ICP emission spectroscopic analyzer [manufactured by Shimadzu Corporation, product number. : ICPE-9000].

The composition ratio of lithium, tungsten, and molybdenum was determined from the content of each element measured above and the total amount (equivalent) of tungsten and molybdenum determined based on the formula (II), and the composition ratio was the synchrotron radiation powder. It can be confirmed whether or not it matches the coating compound identified by the X-ray diffraction method (SXRD).

For example, as described in Example 1 described later, the amount of tungsten oxide (WO ₃ ) with respect to 100 g of the base metal powder is adjusted to 0.23 g (tungsten (W) equivalent amount: 0.18 g), and tungsten oxide is used. Is added to the base metal powder as a coating raw material, in the entire positive electrode active material (dried product) of lithium contained in the coating compound (coating layer) existing on the surface of the obtained positive electrode active material (dried product). When the content is 0.014% by mass and the content of tungsten contained in the coating compound (coating layer) in the positive electrode active material (dried product) is 0.20% by mass, per 5 g of the positive electrode active material. It contains 0.1 mmol (0.7 mg) of lithium and 0.05 mmol (10 mg) of tungsten, and the composition ratio of lithium to tungsten (lithium / tungsten) is 2.

Further, for example, as described in Example 1 described later, when the coating compound identified by the radiation powder X-ray diffraction method (SXRD) is only dilithium ditungstate (Li ₂ WO ₄ ), the present invention is applicable. Since Li ₂ WO ₄ is composed of 2 mol of lithium, 1 mol of tungsten and 4 mol of oxygen, the composition ratio of lithium and tungsten (lithium / tungsten) is 2, and the multi-type ICP emission spectroscopic analyzer [(Co., Ltd.) ) Shimadzu Seisakusho Co., Ltd., Part No .: ICPE-9000], which matches the composition ratio of lithium and tungsten (lithium / tungsten) 2 determined by a chemical analysis method.

In this way, the fact that the coating compound identified by the synchrotron radiation powder X-ray diffraction method (SXRD) is coated on the particle surface of the base metal powder is the analysis result by the physical characteristic analysis method and the analysis result by the chemical analysis method. It can be evaluated by confirming that and matches. The reliability of the analysis results can be improved by performing both the physical characteristic analysis method and the chemical analysis method rather than performing only one of the physical characteristic analysis method and the chemical analysis method. ..

As shown in Comparative Example 9 below, when 100 g of base metal powder and 1.04 g of dilithium ditungsten (Li ₂ WO ₄ ) (equivalent amount of tungsten: 0.73 g) are mixed as a coating compound, the positive electrode activity is activated. When the content of thium in the substance (dried product) is 0.13% by mass and the content of tungsten is 0.73% by mass, the amount of lithium per 5 g of the positive electrode active material is 0.9 mmol (6.5 mg). ), The amount of tungsten is 0.2 mmol (36 mg), and the composition ratio of lithium and tungsten (ratio of the number of atoms of lithium / tungsten) is 5.

However, when the only coating compound identified by synchrotron radiation powder X-ray diffraction (SXRD) is dilithium ditungstate (Li ₂ WO ₄ ), the composition ratio of lithium to tungsten (lithium / tungsten), as described above. However, in Comparative Example 9, it does not match that the composition ratio of lithium and tungsten obtained by the ICP method, which is a chemical analysis method, is 5. From this, it is recognized that the coating compound contains lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) in addition to dilithium ditungstate (Li ₂ WO ₄ ).

(F) Lithium content in the base metal powder after preparation of the positive electrode active material When the positive electrode active material is prepared, the amount of the coating raw material is the excess lithium present on the surface of the secondary particles of the base metal powder. When the amount is larger than the amount of the compound (when lithium is insufficient), as described above, lithium is deprived of the base metal powder, so that the obtained positive electrode active material fully exhibits its performance as a positive electrode active material. It may not be possible.

The lithium salt constituting the coating layer of the positive electrode active material is insoluble in an organic solvent and easily soluble in water. Therefore, the positive electrode active material is immersed in water, the coating layer is dissolved to isolate the base metal powder, and the base material powder is completely dissolved with an inorganic acid or the like to obtain lithium contained in the base material powder. An analytical sample solution for measuring the content can be prepared. More specifically, the lithium content in the base metal powder can be measured by the following method.

[Method of measuring lithium content in base metal powder after preparation of positive electrode active material]
A slurry is prepared by mixing 5 g of the positive electrode active material and 100 mL of pure water at room temperature, and the coating layer existing on the surface of the base metal powder is dissolved in water by stirring the slurry for 10 minutes. , The slurry is filtered, and the obtained cake-like solid content is recovered.

The recovered solid content is added to an inorganic acid such as 35% hydrochloric acid and heated to a temperature of about 100 to 200 ° C. for thermal decomposition, so that the total volume of the obtained decomposition liquid is 200 mL. An analytical sample solution is prepared by adding pure water to the mixture.

By appropriately diluting the analytical sample solution obtained above and measuring the amount of lithium in the analytical sample solution using a multi-type ICP emission spectroscopic analyzer [manufactured by Shimadzu Corporation, product number: ICPE-9000]. , The lithium content in the base metal powder after the production of the positive electrode active material can be specified.

As described above, according to the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention, the coating compound constituting the coating layer having a resistance reducing function is coated on the particle surface of the base material powder. It is possible to efficiently obtain a positive electrode active material for a lithium ion secondary battery in which the thickness of the coating layer is optimized and the variation in the thickness of the coating layer (coefficient of variation CV%) is suppressed.

Therefore, the positive electrode active material for a lithium ion secondary battery of the present invention suppresses gelation during preparation of a positive electrode mixture paste when the positive electrode active material is used in a non-aqueous electrolyte lithium ion secondary battery. Therefore, the quality and safety of the secondary battery can be improved, and when the positive electrode active material is used in the all-solid-state lithium-ion secondary battery, the formation of different interfaces is suppressed and the coating layer Since the thickness is uniform and uniform, it is possible to improve the battery characteristics after manufacturing the lithium ion secondary battery.

(G) Schematic Description of Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for lithium ion secondary battery of the present invention will be described below with reference to FIG. FIG. 1 is a schematic explanatory view showing an embodiment of a positive electrode active material for a lithium ion secondary battery of the present invention.

FIG. 1A shows a state in which the primary particles 1 of the base material powder are aggregated to form the secondary particles 2. Since the secondary particles 2 of the base metal powder do not form a coating layer having high lithium ion conductivity such as lithium tungstate and lithium molybdate, intercalation of lithium ions into the crystal lattice indicated by arrow A. Since deintercalation to the crystal lattice indicated by the ion and the arrow B is not actively performed, when the secondary particles 2 are used in the lithium ion secondary battery, the positive electrode resistance becomes high and the retention rate of the discharge capacity is increased. Is considered to be low.

On the other hand, in the positive electrode active material for a lithium ion secondary battery of the present invention, as shown in FIG. 1 (b), the primary particles 1 are aggregated to form the secondary particles 2, and the secondary particles 2 are further formed. Since the coating layer 3 is formed on the surface of the particles 2, the high lithium ion conductivity of the coating layer 3 causes the intercalation of lithium ions to the crystal lattice indicated by the arrow C and the crystal indicated by the arrow D. Since deintercalation to the lattice is actively performed, it is considered that when the secondary particles 2 are used in the lithium ion secondary battery, the positive electrode resistance is reduced and the maintenance rate of the discharge capacity is improved.

2. 2. Lithium Ion Secondary Battery The lithium ion secondary battery of the present invention is characterized by having a positive electrode containing a positive electrode active material for a lithium ion secondary battery.

The components of the lithium ion secondary battery of the present invention may be the same as the components of a commonly used lithium ion secondary battery, and are not particularly limited. For example, when the lithium ion secondary battery of the present invention is a non-aqueous electrolyte lithium ion secondary battery, it includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution. Further, when the lithium ion secondary battery of the present invention is an all-solid-state lithium-ion secondary battery, it includes a positive electrode, a negative electrode, and a solid electrolyte.

The embodiments of the lithium ion secondary battery of the present invention described below are examples, and embodiments in which various modifications or improvements are made to the embodiments based on the knowledge of those skilled in the art are included in the scope of the present invention. Will be done.

(1) Non-aqueous electrolyte lithium-ion secondary battery [Positive electrode]
First, a positive electrode mixture is prepared by mixing the positive electrode active material, the conductive material and the binder of the present invention. A positive electrode mixture paste is obtained by adding components such as activated carbon and an organic solvent used for adjusting the viscosity to the positive electrode mixture as necessary and further kneading the obtained mixture.

The ratio of each component in the positive electrode mixture is an important factor in determining the performance of the lithium ion secondary battery. The ratio of each component in the positive electrode mixture is not particularly limited. The solid content of the positive electrode mixture from which the organic solvent has been removed includes 60 to 95% by mass of the positive electrode active material, 1 to 20% by mass of the conductive material, and a binder (binder), as in the case of the positive electrode of a general lithium secondary battery. ) 1 to 20% by mass is preferably contained.

Next, the positive electrode mixture paste can be obtained by applying the positive electrode mixture paste to the surface of a current collector made of, for example, aluminum foil, and drying the paste to volatilize and remove the organic solvent. If necessary, the positive electrode may be pressurized by using a roll press or the like in order to increase the electrode density.

The positive electrode is obtained as described above, and the positive electrode usually has a sheet shape. The positive electrode is used when manufacturing a battery after cutting it to an appropriate size as needed.

The present invention is not limited to the method for producing the positive electrode, and the positive electrode may be produced by another method for producing the positive electrode.

As the conductive material, for example, graphite such as natural graphite, artificial graphite, expanded graphite, carbon black such as acetylene black, and Ketjen black can be used. The binder has a role of binding the particles of the positive electrode active material, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, ethylene-propylene-diene rubber, fluororesin such as fluororubber, and styrene-. Olefin-based resins such as butadiene rubber, cellulose-based resin, acrylic resin, polypropylene, and polyethylene can be used.

After preparing the positive electrode mixture by mixing the positive electrode active material, the conductive material and the binder, an organic solvent is added to the positive electrode mixture to dissolve the binder, and the mixture is kneaded to form the positive electrode. A material paste may be prepared. For the organic solvent, for example, N-methyl-2-pyrrolidone (NMP) or the like can be used. Activated carbon may be added to the positive electrode mixture, if necessary, in order to increase the capacity of the electric double layer.

[Negative electrode]
For the negative electrode, a negative electrode mixture paste is prepared by mixing a negative electrode active material that occludes and desorbs metallic lithium, a lithium alloy, or lithium ions with a binder, and adding an organic solvent to the obtained mixture. The negative electrode mixture paste can be produced by applying the negative electrode mixture paste on the surface of a current collector made of a metal foil such as a copper foil, and drying the mixture to volatilize and remove the organic solvent. If necessary, the negative electrode may be pressurized by using a roll press or the like in order to increase the electrode density.

As the negative electrode active material, for example, a calcined body of an organic compound such as natural graphite, artificial graphite, or phenol resin, or a powdered body of a carbon substance such as coke can be used. Similar to the positive electrode, the negative electrode binder includes, for example, a fluororesin-based binder such as polyvinylidene fluoride (PVDF), a water-based binder such as styrene-butanediene rubber, and a negative electrode. An organic solvent such as N-methyl-2-pyrrolidone (NMP) used for dispersing the active material and the binder can be used. An appropriate amount of a viscosity modifier such as carboxymethyl cellulose (CMC) may be used in the negative electrode active material in order to improve the binding force.

[Separator]
A separator is arranged between the positive electrode and the negative electrode. The separator is used to separate the positive electrode and the negative electrode and retain the electrolyte. As the separator, for example, a film in which a large number of fine through holes are formed in a fimul made of a resin such as polyethylene or polypropylene can be used.

[Non-aqueous electrolyte]
The non-aqueous electrolyte solution is a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and trifluoropropylene carbonate (TFPC); dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl. Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC); ether compounds such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), dimethoxyethane (DME); ethylmethylsulfone, 1,4 -Sulfur compounds such as butane sulton, phosphate ester compounds such as triethyl phosphate, trioctyl phosphate and the like can be mentioned, but the present invention is not limited to these examples. Each of these organic solvents may be used alone, or two or more kinds may be used in combination.

Examples of the supporting salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiAsF ₆ ), and lithium bis (trifluo). Examples thereof include lomethanesulfonyl) imide [LiN (CF ₃ SO ₂ ) ₂ ] and composite salts thereof, but the present invention is not limited to such examples. Each of these supporting salts may be used alone, or two or more types may be used in combination.

The non-aqueous electrolyte solution may contain additives such as a radical scavenger, a surfactant, and a flame retardant as long as the object of the present invention is not impaired.

[Shape and configuration of lithium-ion secondary battery]
The lithium ion secondary battery composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution may have various shapes such as a cylindrical type and a laminated type. Regardless of the shape of the lithium ion secondary battery, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with a non-aqueous electrolytic solution. A current collecting lead or the like is connected between the positive electrode and the positive electrode terminal communicating with the outside and between the negative electrode and the negative electrode terminal communicating with the outside.

A lithium ion secondary battery can be completed by storing the electrode body having the above configuration in the battery case and sealing the battery case.

〔Characteristic〕
A. Positive electrode resistance A Nyquist plot can be obtained by producing a 2032 type coin battery CBA, charging the coin battery CBA at a charging potential of 4.1 V, and measuring it by the AC impedance method using a frequency response analyzer and a potentiogalvanostat. Since this Nyquist plot is represented as the sum of the solution resistance, the negative electrode resistance and its capacitance, and the positive electrode resistance and its capacitance, the fitting calculation is performed using an equivalent circuit based on the Nyquist plot. , Positive electrode resistance can be calculated.

B. Initial discharge capacity and maintenance rate of discharge capacity The initial discharge capacity is set to the current density with respect to the positive electrode after the open circuit voltage OCV (Open-Circuit-Voltage) is stabilized by leaving it for about 24 hours from the time of manufacturing the 2032 type coin battery CBA. This is the discharge capacity when the battery is charged to a cutoff voltage of 4.3 V at 0.1 mA / cm ² and discharged to a cutoff voltage of 3.0 V after a one-hour rest.

The maintenance rate of the discharge capacity is determined by holding the temperature of the coin battery CBA at 60 ° C. and measuring the discharge capacity (initial discharge capacity) of the first cycle, then resting for 10 minutes, and similarly to the measurement of the initial discharge capacity. The charge / discharge cycle is repeated for 500 cycles (charge / discharge) including the measurement of the initial discharge capacity, and the discharge capacity at the 500th cycle is measured.
[Discharge capacity maintenance rate (%)]
= [(Discharge capacity at the 500th cycle) ÷ (Initial discharge capacity)] × 100
It is a value obtained based on.

(2) All-solid-state lithium-ion secondary battery [positive electrode]
The positive electrode, the positive electrode active material powder and Li ₂ S-P ₂ S ₅ based glass, a sulfide-based lithium ion conductive solid electrolyte powder such as Li ₁₀ GeP ₂ S ₁₂ in a suitable ratio (e.g., weight ratio 7 : The mixture obtained by mixing in 3) can be used.

[Negative electrode]
For the negative electrode, an appropriate ratio (for example, 7: by mass ratio) of a negative electrode active material capable of occluding and desorbing metallic lithium, lithium-indium alloy or lithium ions and a sulfide-based lithium ion conductive solid electrolyte powder is used. The mixture obtained by mixing in 3) can be used. As the negative electrode active material, for example, a calcined body of an organic compound such as natural graphite, artificial graphite, or phenol resin, or a powdered body of a carbon substance such as coke can be used.

[Solid electrolyte]
The solid electrolyte is preferably a lithium ion conductor having an ionic conductivity of 10 ^-4 S / cm or more, such as a sulfide-based lithium ion conductive solid electrolyte. The sulfide-based lithium ion conductive solid electrolyte, for _{example, Li 2 S-P 2 S} 5 -based glass, Li ₁₀ GeP ₂ S ₁₂ based glass, such as _{Li 3 PO 4 -Li 2 S-} SiS 2 based glass like However, the present invention is not limited to such examples.

[Shape and configuration of all-solid-state lithium-ion secondary battery]
The all-solid-state lithium-ion secondary battery has a positive electrode, a negative electrode, and a solid electrolyte as described above. Examples of the shape of the all-solid-state lithium ion secondary battery include a circular type and a sheet type. Regardless of the shape of the all-solid lithium-ion secondary battery, the positive electrode and the negative electrode are the electrode bodies, the solid electrolyte exists between the positive electrode and the negative electrode, and the positive electrode current collector provided on the positive electrode is provided. Connect between the positive electrode terminal leading to the outside and between the negative electrode current collector provided on the negative electrode and the negative electrode terminal leading to the outside with a current collecting lead or the like, and store these in a battery case to seal them. Thereby, an all-solid-state lithium ion secondary battery can be obtained.

〔Characteristic〕
A. Positive electrode resistance For the positive electrode resistance, the all-solid-state battery is charged to a charging potential of 4.0 V, the AC impedance is measured using a frequency response analyzer and a potentiogal vanostat, and the positive electrode resistance is calculated from the obtained impedance spectrum using an equivalent circuit. It is the value when.

B. Initial discharge capacity and retention rate of discharge capacity The initial discharge capacity is the capacity when an all-solid-state battery is manufactured, charged to a charging potential of 4.2 V at a constant current density, and discharged to 3.0 V. In addition, the maintenance rate of the discharge capacity is 50 cycles including the measurement of the initial discharge capacity, which is the same as the measurement of the initial discharge capacity after the initial discharge capacity is measured by holding the all-solid-state battery at 25 ° C. (Charging / discharging) Repeatedly measure the discharge capacity at the 50th cycle, and formula:
[Discharge capacity maintenance rate (%)]
= [(Discharge capacity at 50th cycle) ÷ (Initial discharge capacity)] × 100
It is a value obtained based on.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.

In each example, the base metal powder, the positive electrode active material, and each reagent used in producing the lithium ion secondary battery are all special grade reagents manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. Table 1 shows the results of analysis and identification of the base metal powder and the positive electrode active material.

[Example 1]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.81 and a tap density of 2.6 g / cm ³ and a pH of the base material powder slurry of 11.0 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The powder of the lithium metal composite oxide so that the equivalent of tungsten contained in the coating compound to be produced is one equivalent with respect to the excess lithium of the lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g was adjusted to be the amount described in the column of "total amount of W and Mo" in Table 1, and the first obtained above was obtained. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 4 nm, and the coefficient of variation CV% indicating the variation in thickness was 15%. Further, the pH of the slurry of the positive electrode active material is 9.5, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

The lithium content of the base metal powder after preparation of the positive electrode active material (listed in the column of "Li in the base material powder" in Table 1) was 7.1% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.27. Moreover, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 90%.

The positive electrode resistance value and the retention rate of the discharge capacity of the lithium ion secondary battery were measured based on the following methods.

[Measurement method of positive electrode resistance value and discharge capacity maintenance rate]
15 mg of a mixture obtained by mixing a positive electrode active material and 75 Li ₂ S-25P ₂ S ₅ glass at a mass ratio of 7: 3 was used for the positive electrode. Also, artificial graphite as a negative electrode 75Li ₂ S-25P ₂ S ₅ mass and glass ratio of 7: with a mixture 6mg obtained by mixing 3. As the solid electrolyte, 150 mg of 75 Li ₂ S-25P ₂ S ₅ glass was used.

The positive electrode, the solid electrolyte, and the negative electrode were superposed to prepare a three-layer laminated body, and the obtained laminated body was pressure-molded to a diameter of 10 mm at a pressure of 300 MPa, and stainless steel plates were formed on both sides of the obtained molded body. Was pressure-welded to form a current collector, and a circular all-solid-state lithium-ion secondary battery was produced.

(1) Positive electrode resistance value The all-solid-state lithium-ion secondary battery obtained above is charged with a charging potential of 4.0 V, and an AC impedance is used using a frequency response analyzer and Potential Galvanostat 1255B (trade name, manufactured by Solartron, UK). The impedance spectrum was obtained by measuring by the method. In the impedance spectrum obtained above, two semicircles were observed in the high frequency region and the intermediate frequency region, and the positive electrode resistance value was calculated by analyzing the semicircles in the intermediate frequency region with an equivalent circuit.

(2) Maintenance rate of discharge capacity Using the all-solid-state lithium-ion secondary battery obtained above, the battery is charged in air at 25 ° C. with a constant current density until the potential reaches 4.2 V, and then the potential becomes 3. The initial discharge capacity when discharged to 0 V is measured.

After measuring the initial discharge capacity, charging and discharging were repeated for 50 cycles including the measurement of the initial discharge capacity in the same manner as the measurement of the initial discharge capacity, and then the discharge capacity at the 50th cycle was measured, and the formula (III):
[Discharge capacity maintenance rate (%)]
= {[Discharge capacity at a predetermined point in time (mAh or Ah)]
÷ [Initial discharge capacity (mAh or Ah)]} × 100 (III)
The maintenance rate of the discharge capacity was calculated based on.

[Example 2]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.6 g / cm ³ , and a pH of the base metal powder slurry of 11.3 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The powder of the lithium metal composite oxide so that the equivalent of tungsten contained in the coating compound to be produced is one equivalent with respect to the excess lithium of the lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g was adjusted to be the amount described in the column of "total amount of W and Mo" in Table 1, and the first obtained above was obtained. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 7 nm, and the coefficient of variation CV% indicating the variation in thickness was 12%. Further, the pH of the slurry of the positive electrode active material is 9.7, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.24. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 91%.

[Example 3]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.7 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.7 g / cm ³ , and a pH of the base metal powder slurry of 11.6 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 14 nm, and the coefficient of variation CV% indicating the variation in thickness was 8.6%. Further, the pH of the slurry of the positive electrode active material is 9.7, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.18. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 92%.

[Example 4]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. Particle size] was 0.81, the tap density was 2.6 g / cm ³ , and the base metal powder slurry had a pH of 11.9. A lithium metal composite oxide powder was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 29 nm, and the coefficient of variation CV% indicating the variation in thickness was 5.2%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.11. In addition, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 93%.

[Example 5]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.80, a tap density of 2.6 g / cm ³ , and a pH of the base material powder slurry of 12.2 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 57 nm, and the coefficient of variation CV% indicating the variation in thickness was 3.4%. Further, the pH of the slurry of the positive electrode active material is 9.5, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.15. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 92%.

[Example 6]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.7 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.7 g / cm ³ and a pH of the base metal powder slurry of 12.5 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 116 nm, and the coefficient of variation CV% indicating the variation in thickness was 5.1%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.22. Moreover, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 90%.

[Example 7]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.0 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.81 and a tap density of 2.5 g / cm ³ and a pH of the base material powder slurry of 11.5 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and molybdenum trioxide (MoO ₃ ) with the temperature of the first mixture adjusted to 30 ° C.

Next, the second mixture obtained above was dried at a temperature of 170 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 10 nm, and the coefficient of variation CV% indicating the variation in thickness was 11%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.20. Moreover, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 90%.

[Example 8]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.1 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.80, a tap density of 2.5 g / cm ³ , and a pH of the base material powder slurry of 12.0 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and molybdenum trioxide (MoO ₃ ) with the temperature of the first mixture adjusted to 30 ° C.

Next, the second mixture obtained above was dried at a temperature of 170 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 33 nm, and the coefficient of variation CV% indicating the variation in thickness was 6.2%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.13. In addition, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 93%.

[Example 9]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.1 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.5 g / cm ³ , and a pH of the base material powder slurry of 12.4 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and molybdenum trioxide (MoO ₃ ) with the temperature of the first mixture adjusted to 30 ° C.

Next, the second mixture obtained above was dried at a temperature of 170 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 82 nm, and the coefficient of variation CV% indicating the variation in thickness was 4.3%. Further, the pH of the slurry of the positive electrode active material is 9.5, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.19. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 91%.

[Example 10]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.9 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.5 g / cm ³ , and a pH of the base material powder slurry of 12.1 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 6 g of water.

As a coating raw material, a mixture of coating raw materials obtained by mixing tungsten trioxide (WO ₃ ) and molybdenum trioxide (MoO ₃ ) at a molar ratio of 1: 1 was used. The lithium metal is prepared so that the total amount of tungsten and molybdenum contained in the produced coating compound is 1 equivalent with respect to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The total amount of tungsten and molybdenum contained in the mixture of the coating raw materials per 100 g of the powder of the composite oxide was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1, and described above. A second mixture was obtained by mixing the first mixture and the mixture of the coating raw materials in a state where the temperature of the obtained first mixture was adjusted to 35 ° C.

Next, the second mixture obtained above was dried at a temperature of 200 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, the coating compounds were lithium tungstate and lithium molybdate, and their compositions were dilithium ditungstate (Li ₂ WO ₄ ) and dimolybdate. It was confirmed to be dilithium (Li ₂ MoO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 45 nm, and the coefficient of variation CV% indicating the variation in thickness was 4.4%. Further, the pH of the slurry of the positive electrode active material is 9.7, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.16. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 92%.

The positive electrode resistance value of the lithium ion secondary battery produced using the positive electrode active material obtained above is the lithium ion secondary battery produced using the positive electrode active material obtained in Comparative Example 13 (without coating). When the positive electrode resistance value of the above was 1.00, it was 0.16, and it was confirmed that the maintenance rate of the discharge capacity of the lithium ion secondary battery was 92%.

[Comparative Example 1]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.80, a tap density of 2.6 g / cm ³ , and a pH of the base material powder slurry of 10.5 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 1 nm, and the coefficient of variation CV% indicating the variation in thickness was 82%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.58. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 85%.

[Comparative Example 2]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.7 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.6 g / cm ³ , and a pH of the base material powder slurry of 13.0 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) with the temperature of the first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 360 nm, and the coefficient of variation CV% indicating the variation in thickness was 18%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.40. In addition, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 86%.

[Comparative Example 3]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.0 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.81 and a tap density of 2.5 g / cm ³ and a pH of the base material powder slurry of 10.8 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The powder of the lithium metal composite oxide so that the equivalent amount of molybdenum contained in the coating compound to be produced is 1 equivalent with respect to the excess lithium of the lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1, and the first obtained above. A second mixture was obtained by mixing the first mixture and molybdenum trioxide (MoO ₃ ) with the temperature of the mixture adjusted to 30 ° C.

Next, the second mixture obtained above was dried at a temperature of 170 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the coating layer of the positive electrode active material was 2 nm, and the coefficient of variation CV% indicating the variation in thickness was 53%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0. It was confirmed that it was less than 003% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.61. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 85%.

[Comparative Example 4]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.1 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.82, a tap density of 2.5 g / cm ³ , and a pH of the base metal powder slurry of 12.8 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and obtained as described above. A second mixture was obtained by mixing the first mixture and molybdenum trioxide (MoO ₃ ) with the temperature of the first mixture adjusted to 30 ° C.

Next, the second mixture obtained above was dried at a temperature of 170 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the positive electrode active material was 206 nm, and the coefficient of variation CV% indicating the variation in thickness was 19%. Further, the pH of the slurry of the positive electrode active material is 9.7, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.44. In addition, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 86%.

[Comparative Example 5]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. A lithium metal composite oxide having a particle size of 0.81 and a tap density of 2.6 g / cm ³ and a pH of the base material powder slurry of 11.8 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder was adjusted to be the amount shown in the column of "total amount of W and Mo" in Table 1, and the first mixture and the third were adjusted. A second mixture was obtained by mixing with tungsten oxide (WO ₃ ) at room temperature.

Next, the second mixture obtained above was dried at a temperature of 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the positive electrode active material was 23 nm, and the coefficient of variation CV% indicating the variation in thickness was 17%. Further, the pH of the slurry of the positive electrode active material is 9.5, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.32. The retention rate of the discharge capacity of the lithium ion secondary battery obtained above was 87%.

[Comparative Example 6]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.0 μm, and the particle size distribution [(d90-d10) / average. A lithium metal composite oxide having a particle size of 0.80, a tap density of 2.5 g / cm ³ , and a pH of the base metal powder slurry of 11.7 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the coating compound to be produced is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g of the powder was adjusted so as to be the amount shown in the column of "total amount of W and Mo" in Table 1, and the first mixture and the third A second mixture was obtained by mixing with molybdenum oxide (MoO ₃ ) at room temperature.

Next, the second mixture obtained above was dried at 170 ° C. for 12 hours, and then a part of the agglomerates was decoagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the positive electrode active material was 16 nm, and the coefficient of variation CV% indicating the variation in thickness was 16%. Further, the pH of the slurry of the positive electrode active material is 9.5, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.38. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 87%.

[Comparative Example 7]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.8 μm, and the particle size distribution [(d90-d10) / average. A lithium metal composite oxide having a particle size of 0.82, a tap density of 2.6 g / cm ³ and a pH of the base material powder slurry of 12.1 was used.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium metal composite oxide is prepared so that the equivalent of tungsten contained in the produced coating compound is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the powder was adjusted to be the amount shown in the column of "total amount of W and Mo" in Table 1, and the first mixture and the third were adjusted. Mixture A was obtained by mixing with tungsten oxide (WO ₃ ) at room temperature.

Next, a mixture B was obtained by mixing 100 g of the mixture A obtained above and 7 g of water. The obtained mixture B was dried at 230 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the positive electrode active material was 45 nm, and the coefficient of variation CV% indicating the variation in thickness was 23%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.65. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 85%.

[Comparative Example 8]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.0 μm, and the particle size distribution [(d90-d10) / average. A lithium metal composite oxide having a particle size of 0.82, a tap density of 2.5 g / cm ³ and a slurry pH of 12.2 was used.

Molybdenum trioxide (MoO ₃ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the coating compound to be produced is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the molybdenum trioxide (MoO ₃ ) per 100 g of the powder was adjusted so as to be the amount shown in the column of "total amount of W and Mo" in Table 1, and the first mixture and the third Mixing with molybdenum oxide (MoO ₃ ) at room temperature gave Mixture A.

Next, a mixture B was obtained by mixing 100 g of the mixture A obtained above and 4 g of water. The obtained mixture B was dried at 170 ° C. for 12 hours, and then a part of the agglomerates was coagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium molybdate and its composition was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the positive electrode active material was 51 nm, and the coefficient of variation CV% indicating the variation in thickness was 33%. Further, the pH of the slurry of the positive electrode active material is 9.6, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.77. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 85%.

[Comparative Example 9]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.7 μm, and the particle size distribution [(d90-d10) / average. A lithium metal composite oxide having a particle size of 0.81 and a tap density of 2.6 g / cm ³ and a slurry pH of 11.6 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Dilithium ditungstate (Li ₂ WO ₄ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of tungsten contained in the coating compound to be produced is 1 equivalent to the amount of lithium in the excess lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the dilithium ditungstate (Li ₂ WO ₄ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and described above. A second mixture was obtained by mixing the first mixture and dilithium ditungstate (Li ₂ WO ₄ ) with the temperature of the obtained first mixture adjusted to 40 ° C.

Next, the second mixture obtained above was dried at 230 ° C. for 12 hours, and then a part of the agglomerates was decoagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, lithium hydroxide and lithium carbonate (Li ₂ CO ₃ ) were detected as impurities in addition to the identification of lithium tungstate as the coating compound. It was confirmed that the composition of lithium tungstate was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the positive electrode active material was 21 nm, and the coefficient of variation CV% indicating the variation in thickness was 22%. Further, the pH of the slurry of the positive electrode active material is 11.2, the content of lithium hydroxide in the positive electrode active material is 0.076% by mass, and the content of lithium carbonate (Li ₂ CO ₃ ) is 0. It was confirmed to be .006% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.84. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 83%.

[Comparative Example 10]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 12.0 μm, and the particle size distribution [(d90-d10) / average. A powder of a lithium metal composite oxide having a particle size of 0.81 and a tap density of 2.5 g / cm ³ and a slurry pH of 11.5 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 4 g of water.

Dilithium dimolybdate (Li ₂ MoO ₄ ) was used as a coating material. The lithium metal composite oxide is prepared so that the equivalent amount of molybdenum contained in the coating compound to be produced is 1 equivalent to the amount of lithium in the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of molybdenum contained in the dilithium dimolybate (Li ₂ MoO ₄ ) per 100 g of the powder of the above was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1 and described above. A second mixture was obtained by mixing the first mixture and dilithium dimolybate (Li ₂ MoO ₄ ) with the temperature of the obtained first mixture adjusted to 30 ° C.

Next, the second mixture obtained above was dried at 170 ° C. for 12 hours, and then a part of the agglomerates was decoagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, lithium hydroxide and lithium carbonate (Li ₂ CO ₃ ) were detected as impurities in addition to the identification of lithium molybdate. It was confirmed that the composition of lithium was dilithium dimolybdate (Li ₂ MoO ₄ ).

The average thickness of the positive electrode active material was 15 nm, and the coefficient of variation CV% indicating the variation in thickness was 26%. Further, the pH of the slurry of the positive electrode active material is 11.3, the content of lithium hydroxide in the positive electrode active material is 0.096% by mass, and the content of lithium carbonate (Li ₂ CO ₃ ) is 0. It was confirmed that it was .008 mass%.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.89. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 82%.

[Comparative Example 11]
As the base metal powder, the same lithium metal composite oxide powder used in Example 6 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. The lithium equivalent of tungsten contained in the coating compound to be produced is significantly less than one equivalent with respect to the amount of lithium of the surplus lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the metal composite oxide powder was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1, and the above. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) in a state where the temperature of the first mixture obtained in (1) was adjusted to 40 ° C.

Next, the second mixture obtained above was dried at 230 ° C. for 12 hours, and then a part of the agglomerates was decoagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, lithium hydroxide and lithium carbonate (Li ₂ CO ₃ ) were detected as impurities in addition to the identification of lithium tungstate, and tungsten was detected. It was confirmed that the composition of lithium carbonate was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the positive electrode active material was 54 nm, and the coefficient of variation CV% indicating the variation in thickness was 23%. Further, the pH of the slurry of the positive electrode active material is 12.3, the content of lithium hydroxide in the positive electrode active material is 0.95% by mass, and the content of lithium carbonate (Li ₂ CO ₃ ) is 0. It was confirmed to be 0.065% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.96. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 74%.

[Comparative Example 12]
As the base metal powder, the same lithium metal composite oxide powder used in Example 1 was used.

A first mixture was obtained by mixing 100 g of the lithium metal composite oxide powder and 7 g of water.

Tungsten trioxide (WO ₃ ) was used as the coating material. In order to ensure that the equivalent amount of tungsten contained in the coating compound to be produced is significantly more than one equivalent with respect to the amount of lithium in the excess lithium compound contained in the powder of the lithium metal composite oxide. The amount of tungsten contained in the tungsten trioxide (WO ₃ ) per 100 g of the lithium metal composite oxide powder was adjusted so as to be the amount described in the column of "total amount of W and Mo" in Table 1. A second mixture was obtained by mixing the first mixture and tungsten trioxide (WO ₃ ) in a state where the temperature of the first mixture obtained above was adjusted to 40 ° C.

Next, the second mixture obtained above was dried at 230 ° C. for 12 hours, and then a part of the agglomerates was decoagulated with a decoupling machine to obtain a positive electrode active material.

When the coating compound on the particle surface of the positive electrode active material obtained above was identified, it was confirmed that the coating compound was lithium tungstate and its composition was dilithium ditungstate (Li ₂ WO ₄ ).

The average thickness of the positive electrode active material was 36 nm, and the coefficient of variation CV% indicating the variation in thickness was 17%. Further, the pH of the slurry of the positive electrode active material is 9.5, and the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) in the positive electrode active material are both 0.003. It was confirmed that it was less than% by mass.

The lithium content in the base metal powder after the production of the positive electrode active material was 6.9% by mass.

When the positive electrode resistance value of the lithium ion secondary battery produced by using the positive electrode active material obtained in Comparative Example 13 (without coating) described later is 1.00, the positive electrode active material obtained above is used. The positive electrode resistance value of the produced lithium ion secondary battery was 0.91. Further, the maintenance rate of the discharge capacity of the lithium ion secondary battery obtained above was 78%.

[Comparative Example 13]
As the base metal powder, the particle structure is a solid structure, the composition is Li _1.02 Ni _0.82 Co _0.15 Al _0.03 O ₂ , the average particle diameter MV is 11.9 μm, and the particle size distribution is [(d90-d10) / average particle diameter. ] Is 0.82, the tap density is 2.5 g / cm ³ , and the pH of the slurry is 12.1. The powder of the lithium metal composite oxide was used.

The characteristics of the lithium ion secondary battery were evaluated using the lithium metal composite oxide as a positive electrode active material without coating the lithium metal composite oxide. As a result, the positive electrode resistance value of the lithium ion secondary battery was 1.00, and the maintenance rate of the discharge capacity was 67%.

[Comprehensive evaluation]
From the results shown in Table 1, the positive electrode active material obtained in each example has an average thickness of the coating layer in the range of 3 to 150 nm, and has a coefficient of variation (CV%) indicating variation in thickness. It can be seen that it is 15% or less. Further, in the positive electrode active material obtained in each example, the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) were both less than the detection limit of 0.003% by mass. It turns out that there is. Further, in each of the positive electrode active materials obtained in each example, the sum of tungsten and molybdenum contained in the coating compound produced is the sum of the amount of lithium in the excess lithium compound contained in the lithium metal composite oxide. It can be seen that the amount is 0.8 to 1.2 equivalents.

In addition, by synchrotron radiation powder X-ray diffraction method (SXRD), which is a physical characteristic analysis method, dilithium ditungstate (Li ₂ WO ₄ ), dilithium dimolybdate (Li ₂ MoO ₄ ), or a mixture thereof can be used as a coating compound. Identified. The composition ratio of lithium, tungsten and molybdenum [lithium / tungsten, lithium / molybdenum or lithium / (tungsten + molybdenum)] based on the identification result of this radiation powder X-ray diffraction method (SXRD) was performed in parallel with this. Since the composition ratio of lithium [lithium / tungsten, lithium / molybdenum or lithium / (tungsten + molybdenum)] determined based on the contents of lithium, tungsten and molybdenum by the chemical analysis method is consistent, It can be seen that the produced coating compound is as the identification result of the radiation powder X-ray diffraction method (SXRD).

From the above results, in each example, the coating compound having a resistance reducing function is purely coated on the particle surface of the base metal powder in an almost equivalent amount, the thickness of the coating layer is optimized, and the coating layer is optimized. It can be seen that the positive electrode active material for the lithium ion secondary battery is obtained in which the variation in the thickness of the particles is minimized.

Therefore, the positive electrode resistance values of the lithium ion secondary batteries produced using the positive electrode active materials obtained in each example are all less than 0.30, and the retention rate of the discharge capacity is 90% or more. It can be seen that a very good result of being present was obtained.

On the other hand, the positive electrode active materials obtained in each comparative example have the optimum coefficient of variation (CV%) indicating the average thickness of the coating layer and the variation in the thickness, including the one without the coating layer. It is out of the range, and it can be seen that the battery characteristics are inferior.

Further, in Comparative Examples 9 and 10, instead of tungsten acid and molybdic acid, the coating compound dilithium ditungstate (Li ₂ WO ₄ ) or dilithium dimolybate (Li ₂ MoO ₄ ) was used as it was. Therefore, the excess lithium of the lithium compound contained in the base metal powder is mixed into the coating layer as an impurity in an unreacted state, so that lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) are mixed with the coating compound. It is identified and it can be seen that the pH of the slurry of the positive electrode active material exceeds 11. From this, the content of lithium hydroxide was high, and the total amount of tungsten and molybdenum contained in the coating compound was not equivalent to the amount of lithium in the surplus lithium compound contained in the lithium metal composite oxide. .. This tendency is also observed when the amount of the coating raw material for the excess lithium compound contained in the base metal powder with respect to lithium is insufficient, as in the case of the positive electrode active material obtained in Comparative Example 11.

On the other hand, in the positive electrode active material obtained in Comparative Example 12, since the amount of tungsten trioxide (WO ₃ ) added as a coating raw material is excessive, there is a possibility that tungsten trioxide (WO ₃ ) may remain in the coating compound. However, only dilithium ditungsten (Li ₂ WO ₄ ) was identified purely, and the content of lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) were both 0, respectively. It is less than .003% by mass and the coating compound is in the range of 0.8 to 1.2 equivalents.

However, the lithium content of the base material powder of the positive electrode active material obtained in Comparative Example 12 was 6.9% by mass, whereas the lithium content of the positive electrode active material obtained in Example 1 was 6.9% by mass. Since it is 7.1% by mass, it can be seen that in the positive electrode active material obtained in Comparative Example 12, lithium is deprived not only from nickel and cobalt but also from the base material powder itself constituting the composite oxide. ..

Further, the positive electrode resistance value and the retention rate of the discharge capacity of the lithium ion secondary battery are inferior to those of the positive electrode active material obtained in Example 1 than those of the positive electrode active material obtained in Comparative Example 12. In the positive electrode active material obtained in Example 12, it is considered that the battery characteristics were deteriorated due to the deprivation of lithium from the base metal powder itself by the excessive amount of the coating raw material.

As described above, the positive electrode active material for a lithium ion secondary battery of the present invention has a low positive electrode resistance and a high retention rate of discharge capacity when used in a lithium ion secondary battery. Therefore, the lithium ion secondary battery Can be suitably used for.

1 Primary particle 2 Secondary particle 3 Coating layer

In each example, the base metal powder, the positive electrode active material, and each reagent used in producing the lithium ion secondary battery are all special grade reagents manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. The results of analysis and identification of the base metal powder and the positive electrode active material are shown in Tables 1 and 2 .

[Comprehensive evaluation]
From the results shown in Table 2 , the positive electrode active material obtained in each example has an average thickness of the coating layer in the range of 3 to 150 nm, and has a coefficient of variation (CV%) indicating variation in thickness. It can be seen that it is 15% or less. Further, in the positive electrode active material obtained in each example, the content of lithium hydroxide (LiOH) and the content of lithium carbonate (Li ₂ CO ₃ ) were both less than the detection limit of 0.003% by mass. It turns out that there is. Further, in each of the positive electrode active materials obtained in each example, the sum of tungsten and molybdenum contained in the coating compound produced is the sum of the amount of lithium in the excess lithium compound contained in the lithium metal composite oxide. It can be seen that the amount is 0.8 to 1.2 equivalents.

In addition, by synchrotron radiation powder X-ray diffraction method (SXRD), which is a physical characteristic analysis method, dilithium ditungstate (Li ₂ WO ₄ ), dilithium dimolybdate (Li ₂ MoO ₄ ), or a mixture thereof can be used as a coating compound. Identified. The composition ratio of lithium, tungsten and molybdenum [lithium / tungsten, lithium / molybdenum or lithium / (tungsten + molybdenum)] based on the identification result of this radiation powder X-ray diffraction method ( SXRD ) was performed in parallel with this. Since the composition ratio of lithium [lithium / tungsten, lithium / molybdenum or lithium / (tungsten + molybdenum)] determined based on the contents of lithium, tungsten and molybdenum by the chemical analysis method is consistent, It can be seen that the produced coating compound is as the identification result of the radiation powder X-ray diffraction method (SXRD).

Claims (6)

A positive electrode active material for a lithium ion secondary battery, wherein a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide containing lithium, nickel and cobalt are aggregated is used as a raw material. A coating layer containing at least one lithium salt selected from the group consisting of lithium tungstate and lithium molybdate is formed on the surface of the secondary particles, and the average thickness of the coating layer is 3 to 150 nm. A positive electrode active material for a lithium ion secondary battery, characterized in that a fluctuation index (CV%) indicating variation in layer thickness is 15% or less. The lithium according to claim 1, wherein the content of lithium hydroxide (LiOH) in the positive electrode active material is less than 0.003% by mass, and the content of lithium carbonate (Li ₂ CO ₃ ) is less than 0.003% by mass. Positive electrode active material for ion secondary batteries. Lithium metal composite oxide has the formula (I):
_{Li s Ni 1-xy Co x} M y O 2 + α (I)
(In the formula, s, x, y and α are 1.00 ≦ s ≦ 1.30, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.45 and −0.1 ≦ α ≦ 0, respectively. A number satisfying .2, M represents at least one metal element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, W and Al).
The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, which is a lithium metal composite oxide represented by. The lithium ion secondary according to any one of claims 1 to 3, wherein the positive electrode active material for the lithium ion secondary battery is a positive electrode active material for a non-aqueous electrolyte lithium ion secondary battery or a positive electrode active material for an all-solid lithium ion secondary battery. Positive electrode active material for next battery. A lithium ion secondary battery comprising a positive electrode containing the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4. A method for producing a positive electrode active material for a lithium ion secondary battery using a base material powder containing secondary particles in which primary particles of a lithium metal composite oxide containing lithium, nickel and cobalt are aggregated as raw materials.
The first mixture was prepared by mixing the base material powder and water so that the content of water in the mixture of the base material powder and water was 4 to 7% by mass.
The temperature of the first mixture obtained above is adjusted to 25 to 50 ° C., and the second mixture is prepared by mixing the first mixture with the coating raw material.
Including a step of producing a positive electrode active material by drying the second mixture obtained above at a temperature of 150 to 250 ° C. to form a coating layer on the surface of secondary particles contained in the base material powder. ,
A coating material containing at least one compound selected from the group consisting of a tungsten compound and a molybdenum compound is used as the coating material, and the excess lithium compound contained in the base material powder is contained in the coating material for lithium. Adjust the total amount of tungsten and molybdenum to 0.8 to 1.2 equivalents, and adjust the total amount of tungsten and molybdenum per 100 parts by mass of the base metal powder to 0.1 to 6 parts by mass. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4.

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