JP6909553B2 - Film-forming agent and its manufacturing method and non-aqueous electrolyte positive electrode active material for secondary batteries and its manufacturing method - Google Patents

Description

The present invention relates to a film forming agent and a method for producing the same, and a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same.

Since a non-aqueous electrolyte secondary battery is lightweight and has a high energy density, it can be used, for example, as a power source mounted on a vehicle that uses electricity as a drive source, or as a power source used for a personal computer, a mobile terminal, or other electric product. It is becoming more important.

A typical non-aqueous electrolyte secondary battery includes a lithium ion secondary battery that charges and discharges when lithium ions move back and forth between the positive electrode and the negative electrode. In a lithium ion secondary battery having a typical configuration, an electrode material mainly composed of a substance (electrode active material) capable of reversibly storing and releasing lithium ions is layered on a conductive member (electrode current collector). (Hereinafter, such a layered product is referred to as an “electrode mixture layer”, and in the case of a positive electrode, a “positive electrode mixture layer”). For example, in the case of a positive electrode, particles of a lithium transition metal composite oxide as a positive electrode active material, a powder of a highly conductive material (for example, carbon black, etc.), and a binder (for example, polyvinylidene fluoride) are suitable. A paste-like composition (the paste-like composition includes a slurry-like composition and an ink-like composition) is prepared by kneading and dispersing various solvents, and this is used as a positive electrode current collector (for example,). A positive electrode mixture layer is formed by applying it to an aluminum material or the like and drying it.

As the solvent used when preparing the paste-like composition for forming the positive electrode mixture layer, an aqueous solvent or a water-soluble organic solvent (for example, N-methylpyrrolidone or the like) is adopted (for example, Patent Document 1). .. Due to the water content of these solvents, the lithium ions present on the particle surface of the lithium transition metal composite oxide may be eluted into the solvent, and the paste-like composition may exhibit strong alkalinity. In such an alkaline paste-like composition, decomposition of the binder contained in the composition, aggregation of the binder, and aggregation of the positive electrode active material occur, and gelation of the paste-like composition (increase in viscosity) occurs. (A state in which the fluidity and uniformity are lost) is likely to occur. Further, in the case of a water-soluble organic solvent, by working in a place with high humidity, moisture contained in the outside air may flow into the paste-like composition, and gelation of the paste-like composition may occur as well.

Since the gelled paste-like composition has an increased viscosity and a decreased adhesive strength and dispersibility of the raw material powder, it is possible to form a positive electrode mixture layer having a desired thickness and a uniform composition on the positive electrode current collector. It can be difficult. If the thickness and composition are not uniform, the battery reactivity at the time of charging and discharging deteriorates, and further, it causes an increase in the internal resistance of the battery, which is not preferable.

For the purpose of suppressing the paste-like composition, Patent Document 2 describes Li _x Ni _1-y A _y O ₂ (0.98 ≦ x ≦ 1.06, 0.05 ≦ y ≦ 0.30, A. The pH of the supernatant obtained by stirring and mixing 5 g with 100 g of pure water for 120 minutes and then allowing it to stand for 30 seconds is 12.7 or less at 25 ° C. A positive electrode active material for a water electrolyte secondary battery has been proposed.

Further, in Patent Document 3, for the purpose of effectively suppressing the deterioration of the positive electrode active material due to the reaction with the electrolytic solution or the like and improving the cycle characteristics, the surface of the positive electrode active material is an interface formed with a metal organic compound and micellar. By firing the sol-gel step of forming a gel film in which the activator is dispersed and adhered, and the gel film obtained in the sol-gel step, the surfactant is decomposed and removed, and lithium ions are formed on the surface of the positive electrode active material. A method for producing a porous metal oxide-coated positive electrode active material, which comprises a firing step of forming a porous metal oxide-coated layer in which movable pores are formed, has been proposed.

On the other hand, as a technique for solving the above-mentioned problems in the paste-like composition, Patent Document 4 includes a positive electrode and a negative electrode, and the positive electrode is formed on the positive electrode current collector and the current collector. The positive electrode mixture layer includes at least a positive electrode mixture layer containing a positive electrode active material and a binder, and the surface of the positive electrode active material is coated with a hydrophobic film. , A battery which is a binder which dissolves or disperses in an aqueous solvent has been proposed.

JP-A-2009-193805 Japanese Unexamined Patent Publication No. 2003-31222 Japanese Unexamined Patent Publication No. 2009-200007 International Publication No. 2012/1111616

However, Patent Document 2 does not mention a specific method for producing a positive electrode active material for controlling pH. Further, Patent Document 3 does not examine the above-mentioned problems in the paste-like composition used for producing the positive electrode mixture layer.
Further, Patent Document 4 only discloses a method of coating lithium transition metal composite oxide particles by mechanochemical treatment or a general metal alkoxide, and these methods sufficiently provide a coating state. It cannot be controlled, and it is considered that a large amount of coating substance is required to sufficiently prevent the contact between the lithium transition metal oxide particles and the aqueous solvent, and the paste is made while maintaining sufficient battery characteristics. It can be said that it is insufficient as a method for solving the above-mentioned problems in the state composition. Further, the coating method by the mechanochemical treatment has problems such as damage to the surface of the positive electrode active material particles and crushing of the particles themselves.

The present invention has been made to solve the above-mentioned conventional problems, and is a coating film that suppresses gelation of a paste-like composition for forming a positive electrode mixture layer without impairing the battery performance inherent in the positive electrode active material. It is an object of the present invention to provide a forming agent and a method for producing the same, a positive electrode active material for a non-aqueous electrolyte secondary battery, and a method for producing the same.

As a result of diligent studies to solve the above problems, the present inventor chelated a metal compound having a hydrolyzable organic group, mixed water to partially hydrolyze the metal compound, and further. The positive electrode active material produced by using the film forming agent obtained by adding water does not impair the original battery performance of the lithium transition metal composite oxide particles, and can suppress the gelation of the paste-like composition. The present invention was completed with the knowledge that this is the case.

That is, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery in which an oxide film is formed on the surface of lithium transition metal composite oxide particles. A mixed solution containing a metal compound having a hydrolyzable organic group, a chelating agent, and an organic solvent is heated to 50 to 100 ° C. to remove a part of the hydrolyzable organic group contained in the metal compound. A stock solution synthesis step of mixing water with the mixed solution after chelating with the chelating agent to obtain a stock solution containing precursor fine particles produced by partially hydrolyzing the metal compound, and the stock solution. water was mixed, the precursor particles, and the chelating agent, and the organic solvent medium, and the film forming agent synthesized to obtain a film-forming agent comprising water, and the film-forming agent, a lithium transition metal composite A mixing step of mixing the oxide particles to obtain a mixture and drying the mixture to reduce the organic solvent and water in the mixture and the precursor on the surface of the lithium transition metal composite oxide particles. The drying step of forming a film in which fine particles are adsorbed and bonded and the mixture after the drying step are heat-treated to fix the film on the surface of the lithium transition metal composite oxide particles, and the organic component contained in the film. A heat treatment step for obtaining a positive electrode active material on which an oxide film composed of fine metal oxide fine particles is formed is provided, and the positive electrode active material is applied to the surface of the lithium transition metal composite oxide particles. The portion where the oxide film is not formed is dispersed and exists.

As a preferred embodiment of the above-mentioned production method, in the undiluted solution synthesis step, after mixing water with the mixed solution, the solution temperature is maintained at 20 to 90 ° C. to obtain the undiluted solution.
In another preferred embodiment of the above production method, the metal compound having a hydrolyzable organic group comprises one or more selected from zirconium, titanium, and aluminum alkoxides.
In another preferred embodiment of the above production method, the metal compound having a hydrolyzable organic group is selected from zirconium butoxide, titanium isopropoxide, titanium butoxide, aluminum isopropoxide, aluminum diisopropoxide and aluminum butoxide. It consists of one or more types.
As another preferred embodiment in the above-mentioned production method, the chelating agent contains at least one selected from an aminocarboxylic acid salt and a salt thereof and a diketone.
In another preferred embodiment of the production method, the chelating agent comprises acetylacetone.
In another preferred embodiment of the production method, the organic solvent comprises one or more selected from ethanol, 2-propanol and 1-butanol.

The particle size of the hydrolysis product contained in the film-forming agent is preferably a central particle size of 100 nm or less as measured by a dynamic light scattering method.
As a preferred embodiment of the film forming agent, the pH of the film forming agent is 8 to 11.

As a preferable aspect in the method for producing the positive electrode active material, the mixture is mixed using a rotation / revolution type kneading mixer in the mixing step.
As another preferable aspect in the method for producing the positive electrode active material, one or more selected from polyethylene glycol, polypropylene glycol and hexylene glycol are added to the mixture before the drying step.
As another preferable aspect of the method for producing the positive electrode active material, in the heat treatment step, the heat treatment temperature is controlled in the range of 80 to 400 ° C. in an atmosphere selected from an oxygen-containing atmosphere, an inert atmosphere, and a vacuum atmosphere. Heat treatment.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has lithium transition metal composite oxide particles and a coating film covering the surface of the particles, and has an average particle size D50 of 3 to 25 μm measured by a laser diffraction / scattering method. The film is formed of fine particles of one or more oxides selected from zirconium, titanium, and aluminum, and the average particle size D50 of the fine particles is 0.1 to 10 nm, and the fine particles are positive electrode active. The lithium transition metal composite oxide particles contained in an amount of 0.2 to 0.6% by mass based on the entire substance are represented by the following general formula (1), and are described on the surface of the lithium transition metal composite oxide particles. The portion where the oxide film is not formed is dispersed and exists.
General formula: Li _a Ni _1-b M1 _b O ₂ ... (1)
(In the formula, M1 represents one or more elements selected from a transition metal element other than Ni, a group 2 element, or a group 13 element, and 0.95 ≦ a ≦ 1.20, 0 ≦ b ≦ 0. 5.)

As another preferred embodiment of the positive electrode active material, the pH of the slurry 60 minutes after adding 1 g of the positive electrode active material to 50 ml of pure water at 24 ° C. is 11 or less, and the positive electrode active material is 30 ° C.-. The mass increase rate after exposure to a 70% RH constant temperature and humidity chamber for 7 days is 2.0% or less as compared with that before exposure.

The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and includes a positive electrode containing the above-mentioned positive electrode active material.

The positive electrode active material for a non-aqueous electrolyte secondary battery produced by using the film-forming agent of the present invention has a film capable of suppressing elution of tium ions and impairs the battery performance inherent in lithium transition metal oxide particles. The gelation of the paste-like composition can be suppressed even in a solvent containing water. Further, since this positive electrode active material has a coating film, it is not easily affected by the humidity of the outside air, so that gelation is suppressed even if the work is not performed in a place where the humidity is reduced such as a dry room when forming the positive electrode mixture layer. It is possible to improve the handleability during the work process. Further, the method for producing a film-forming agent and a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is simple even in industrial-scale production, and its industrial value is extremely large.

FIG. 1 is a schematic view of a 2032 type coin battery used for battery evaluation.

[Manufacturing method of film forming agent]
The method for producing a film-forming agent of the present embodiment includes a stock solution synthesis step of obtaining a stock solution for film formation, and a film-forming agent synthesis step of mixing water with the stock solution to obtain a film-forming agent. Hereinafter, each step will be described.

(Undiluted solution synthesis process)
In the undiluted solution synthesis step, a mixed solution containing a metal compound having a hydrolyzable organic group, a chelating agent, and an organic solvent is heated to 50 to 100 ° C., water is mixed, and the metal compound is partially hydrolyzed. A stock solution for forming a film obtained by a decomposition reaction is obtained.

As the metal compound, a metal compound having a hydrolyzable organic group can be used. The hydrolyzable organic group refers to a group containing at least a carbon element that can form a hydroxy group (OH group) by hydrolysis when water is added. A metal compound having such a group is easy to hydrolyze, and the metal compound itself is soluble in an organic solvent such as alcohol or water, so that a film-forming agent can be easily synthesized.

Examples of the hydrolyzed organic group include an alkoxy group. Since the metal compound has an alkoxy group, a hydrolysis reaction easily occurs when water is added. Further, in the case of a monomer, the metal compound may have one or more of the above-mentioned groups in one molecule, and preferably has 3 to 4 functional groups in one molecule.

Examples of the alkoxy group include an alkoxy group having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, and a butoxy group. For example, since the ethoxy group is highly reactive and the hydrolysis reaction is likely to occur, when a metal compound having an ethoxy group is used, it is preferably handled in an inert gas. As the alkoxy group, an isopropoxy group and a butoxy group are preferable from the viewpoint of stability and cost.

Examples of the metal compound having an alkoxy group (hereinafter, also referred to as “metal alkoxide compound”) include -ethoxydo, -methoxide, -isopropoxide, and -butoxide. As the metal alkoxide compound, a monomer may be used, or these oligomers may be used. As the oligomer, one that dissolves in an organic solvent used for producing a film-forming agent is used.

Examples of the metal compound having a hydrolyzable organic group include organic group-containing metal compounds such as zirconium, titanium, aluminum, niobium, tin, silicon, boron and phosphorus, and among these, zirconium, titanium and aluminum. It preferably consists of one or more metal alkoxide compounds selected from alkoxides. By using these metal alkoxide compounds as a film-forming agent, it is possible to obtain a positive electrode active material having an oxide film formed of oxide fine particles which are sparingly soluble in water and have a controlled particle size. Such a positive electrode active material can both suppress deterioration of battery characteristics and suppress lithium elution.

Specific examples of the metal compound having a hydrolyzable organic group include zirconium tetrabutoxide, titanium tetraisopropoxide, titanium tetrabutoxide, aluminum triethoxydo, aluminum diisoproxide, aluminum triisopropoxide, and aluminum tributoxide. , Niobpentaethoxydo, tin tetraethoxydo, silanetetraethoxydo, silanetetramethoxyde, boron trimethoxyde, boron triethoxydo, boron triisopropoxide, phosphate trimethoxyde, phosphate triethoxydo, phosphate tributoxide, etc. These metal compounds may be used alone or in combination of two or more. Among these, one or more selected from zirconium tetrabutoxide, titanium tetraisopropoxide, titanium tetrabutoxide, aluminum triisopropoxide, monobutoxyaluminum diisopropoxide and aluminum tributoxide are preferable, and zirconium tetrabutoxide and titaniumium. One or more selected from tetraisopropoxide and titanium tetrabutoxide are more preferable.

The chelating agent can modify (chelate) a part of the hydrolyzable organic group contained in the metal compound to control the rate of the hydrolysis reaction of the metal compound. For example, a metal compound having an alkoxy group has a high hydrolysis rate and may generate a hydroxide due to humidity in the outside air or the like. Therefore, by incorporating a chelating agent in the mixed solution, a part of the hydrolyzable functional groups in the metal compound is modified (chelated) with the chelating agent to suppress the rate of the hydrolysis reaction of the metal compound.

When all the hydrolyzable organic groups are modified, not only the hydrolyzable organic group is not dissolved in the organic solvent, but also the obtained film-forming agent is not adsorbed or chemically reacted on the surface of the composite oxide particles, so that an oxide film is formed. It tends to be insufficient. For example, in the case of zirconium butoxide having four alkoxy groups (butoxy groups) in one molecule, by modifying one or two alkoxy groups with a chelating agent, the stability to the outside air is improved and the particles are formed. It becomes possible to maintain the adsorptivity of.

The chelating agent is not particularly limited, and examples thereof include at least one selected from aminocarboxylic acid and its salt, diketones and its salt. Examples of the diketones include β-diketones and aromatic ketones. Specific examples thereof include aminocarboxylic acids such as nitrilotriacetic acid, methylglycine diacetic acid, dicarboxymethyl glutamic acid and L-aspartic acid, salts thereof, and β-diketone such as acetoacetic acid and acetylacetone. Among these, acetylacetone. Is preferable.

The content of the chelating agent can be appropriately adjusted according to the content of the metal compound having a hydrolyzable organic group and the number of hydrolyzable groups thereof. For example, 5 with respect to 100 parts by mass of the metal compound. It can be ~ 60 parts by mass, preferably 10 to 40 parts by mass. For example, when 1 mol of zirconium tetrabutoxide is chelated, the amount of the four alkoxy groups supplementing one or two functional groups is about the same amount, for example, about 0.5 mol to 2.5 mol. By adding a chelating agent of the above to modify a part of its functional group, the hydrolysis rate is slowed down and the water resistance is greatly improved.

The organic solvent is not particularly limited as long as it can dissolve a metal compound having a hydrolyzable organic group, and for example, alcohols or hydrocarbon-based solvents can be used. Among these, it is preferable to use alcohols from the viewpoint of solubility and dryness. As the alcohols, lower alcohols are preferable, and one or more selected from ethanol, 2-propanol and 1-butanol are more preferable. Ethanol and / or 2-propanol are preferred from the standpoint of additive solubility and cost. By adding a lower alcohol to the mixed solution, drying does not proceed if the solvent of the coating solution finally obtained is only water, and the OH groups remaining on the surface after coating tend to aggregate after drying. In addition to supplementing, effects such as improving the wettability to the surface of the lithium transition metal composite oxide particles can be obtained. It should be noted that higher alcohols and hydrocarbon solvents having 5 or more carbon atoms may cause problems of harmfulness and offensive odor when volatilized and dried.

It is preferable to use a dehydrated organic solvent. By dehydration, the hydrolysis reaction at the time of mixing with a metal compound having a hydrolyzable organic group is suppressed, and the formation of the fine particles is easily controlled by the hydrolysis reaction with water added after the addition of the chelating agent. Can be done.

In the mixed solution, the organic solvent is preferably contained in an amount of 30 parts by mass or more with respect to 100 parts by mass of the metal compound having a hydrolyzable organic group. If the amount of the organic solvent added is less than 30 parts by weight, the reaction with the chelating agent tends to be non-uniform, and white turbidity may occur when water diluted to a concentration suitable for the film-forming agent is added. The upper limit of the content of the organic solvent is not particularly limited, but can be contained in an amount of about 400 parts by mass. Although the mixture can be prepared even if it exceeds 400 parts by weight, there is little merit in terms of cost because the amount of the organic solvent used increases.

The method for preparing the mixed solution is not particularly limited as long as the metal compound having a hydrolyzable organic group is dissolved in an organic solvent and chelated with a chelating agent. For example, a chelating agent can be added to a solution obtained by mixing and dissolving a metal compound and an organic solvent. As a result, the metal compound can be sufficiently modified during chelation. Further, the chelating agent may be added directly, or may be mixed with an organic solvent in advance and added. Further, after adding the chelating agent, for example, heating at 50 to 100 ° C., preferably 60 to 100 ° C., more preferably 70 to 90 ° C. sufficiently chelates the metal compound, and then water is added. When it is added and a partial hydrolysis reaction is carried out, it becomes possible to suppress rapid hydrolysis. The heating time can be appropriately adjusted depending on the type and amount of each component added, and is, for example, 0.2 to 4 hours, more preferably 0.5 to 2 hours.

For example, a monomer of a metal alkoxide compound such as butoxide is dissolved in an organic solvent such as 2-propanol, a chelating agent such as acetylacetone is gradually added to the solution of the obtained solution, and then the mixture is heated at 50 to 100 ° C. , A mixed solution in which the alkoxide monomer is chelated can be obtained. By such an operation, the modification reaction of the alkoxide monomer is promoted and the stability to water is increased.

The amount of each component added can be appropriately adjusted within the above range. For example, the amount of the metal compound added is preferably 10% by mass or more and 65% by mass or less with respect to 100% by mass of the total amount of the obtained mixed solution. More preferably 15% by mass or more and 50% by mass or less, the amount of the chelating agent added is preferably 3% by mass or more and 60% by mass or less, more preferably 3% by mass or more and 30% by mass or less, and the amount of the organic solvent added is preferably 30. It can be adjusted to be 40% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 75% by mass or less.

Next, water is added to the above-mentioned mixed solution to obtain a stock solution (hereinafter, also simply referred to as “stock solution”) of the film-forming agent which is at least partially hydrolyzed (partially hydrolyzed). The stability of the stock solution can be increased by partially hydrolyzing the metal compound having a hydrolyzable organic group. If the metal compound is not partially hydrolyzed, the humidity in the outside air may cause the mixed solution to partially become cloudy, resulting in coagulation and precipitation.

The amount of water added in the partial hydrolysis reaction is preferably 10 parts by mass or more and 50 parts by mass or less, and 15 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the metal compound having a hydrolyzable organic group. The following is more preferable. By adding water in an amount of 10 parts by mass or more, partial hydrolysis of the metal compound can be sufficiently made. On the other hand, when the content is 50 parts by mass or less, the hydrolysis of the metal compound proceeds too rapidly and the undiluted solution can be prevented from gelling.

When water is added to the mixed liquid, a slight cloudiness occurs in the mixed liquid for a moment, but it immediately returns to a transparent liquid. It is probable that this phenomenon was partially hydrolyzed in a state containing organic substances, and at least a part of the hydrolyzable groups became hydroxyl groups, and the water solubility was increased, resulting in an apparently transparent liquid. The mixed liquid to which water is added can then be kept at a liquid temperature of preferably 20 to 90 ° C, more preferably 60 to 90 ° C. Further, in the above temperature range, the mixed solution can be held for preferably 0.2 to 25 hours, more preferably 0.5 to 2 hours. By keeping the liquid temperature and time as described above, the partially hydrolyzed metal compound can be stabilized. By stabilizing the metal compound, it is possible to suppress cloudiness and the formation of precipitates even if a large amount of water is subsequently added for dilution. The mixed solution containing the stabilized metal compound has a storage stability to the extent that the transparency of the undiluted solution does not change even if it is left for one month, for example.

Here, the transparency of the undiluted solution can be evaluated to the extent that visible particles floating in the solution can be confirmed. If it is a coarse particle, it becomes cloudy due to light scattering, and if it is a fine particle (nanoparticle). The liquid is transparent because light is transmitted through it. For example, 50 ml of the undiluted solution is placed in a cylindrical glass container having a diameter of 4 cm and a height of 6 cm, and the appearance of the undiluted solution is visually observed. Here, the nanoparticles refer to fine particles having a central particle size of 100 nm or less. Therefore, the particle size of the particles contained in the undiluted solution is preferably such that the central particle size is 100 nm or less. The central particle size refers to a 50% integrated value (D50) in a volume-based particle size distribution obtained by measuring by a dynamic light scattering method.

The mixed solution or the undiluted solution may contain other additives other than the above-mentioned components as long as the effects of the present invention are not impaired. For example, a water-soluble glycol can be added from the viewpoint of preventing peeling of the coating film in the drying step described later.

The water-soluble glycols may be added at any stage after chelation, but since the glycols are powders, they need to be dissolved in a solvent (water or organic solvent). Therefore, it is preferable to add it at the time of dilution using a large amount of solvent. As the water-soluble glycols, one or more selected from polyethylene glycol, polypropylene glycol and hexylene glycol are preferably used, and among these, polyethylene glycol which is inexpensive, easy to handle, and easily soluble in water or lower alcohol. And / or polypropylene glycol is more preferred, and those having a molecular weight of 2,000 to 20,000 are preferably used. When the polymer has a molecular weight of more than 20,000, its solubility in water or alcohol decreases, so that the film-forming agent may become cloudy. Therefore, it is necessary to sufficiently dissolve the film-forming agent in the film-forming agent by selecting an organic solvent or the like. There is. The amount of the water-soluble glycol added is preferably about 2 to 20 parts by mass with respect to 100 parts by mass of the metal compound (addition amount) having a hydrolyzable organic group.

(Film forming agent synthesis process)
The film-forming agent synthesis step is a step of mixing water with the above-mentioned undiluted solution to obtain a film-forming agent. The film-forming agent contains fine particles (hereinafter, referred to as “precursor fine particles”) that are precursors of an oxide film formed on at least a part of the particle surface of the lithium transition metal composite oxide. The precursor fine particles refer to particles derived from a metal compound having a hydrolyzable organic group, which is obtained when water is mixed with the above-mentioned mixed solution or undiluted solution. It is considered that the main precursor fine particles are produced by hydrolyzing at least a part of the hydrolyzable organic groups contained in the metal compound. The stock solution may be mixed with water alone or a mixed solution of water and alcohol. When this mixed solution is a mixed solution in which 10 to 50 parts by mass of alcohol is mixed with 100 parts by mass of water, drying proceeds easily and productivity is improved. As the alcohol that can be used here, one or more kinds are selected from ethanol, 2-propanol and 1-butanol.

The precursor fine particles can be uniformly deposited on the particle surface of the lithium transition metal composite oxide in the mixing step described later by diluting the stock solution with water to reduce the concentration. When water is not mixed with the stock solution, the concentration of the stock solution is relatively high, so the precursor fine particles are locally adsorbed on the particle surface of the lithium transition metal composite oxide, and an oxide film is formed only on a part of the particle surface. It may end up.

The dilution ratio of the undiluted solution with water (or a mixed solution of water and alcohol) can be appropriately adjusted so that the amounts of water and precursor fine particles in the mixture in the mixing step described later are in the optimum range. For example, it can be diluted with water (or a mixed solution of water and alcohol) of preferably 50% by volume or more and 500% by volume or less, more preferably 100% by volume or more and 400% by volume or less with respect to 100% by volume of the undiluted solution. The content of the precursor fine particles can be, for example, 0.5 mmol or more and 10 mmol or less, preferably 0.5 mmol or more and 8 mmol or less, and more preferably 0.5 mmol or more and 5 mmol or less with respect to 10 ml of the film forming agent. When the content of the precursor fine particles is in the above range, the precursor fine particles can be uniformly deposited, and the deterioration of the battery characteristics of the lithium transition metal composite oxide particles can be suppressed. Here, the content of the precursor fine particles is a value that can be calculated from the number of moles of the metal element contained in the added organic group-containing metal compound.
The mass ratio of the precursor fine particles to the water (or a mixed solution of water and alcohol) mixed with the undiluted solution is the case where the amount of the precursor fine particles is converted into the amount of the metal compound having a hydrolyzable organic group. The mass ratio (addition amount of metal compound: water added to the stock solution) is preferably 1: 5 to 50, more preferably 1: 5 to 40.

The method of mixing the undiluted solution and water is not particularly limited, and the undiluted solution and water may be sufficiently mixed. For example, water can be added to the undiluted solution, and the mixture can be mixed by stirring at room temperature for 5 minutes or more. The temperature at the time of mixing is not particularly limited, and may be a temperature of about 15 to 40 ° C., or room temperature.

The amount of the diluted organic solvent and water (hereinafter, both are also collectively referred to as "solvent") is the concentration (addition amount) of the metal compound having a hydrolyzable organic group in the film-forming agent. The total amount is preferably 0.2 parts by mass or more and 20 parts by mass or less, and more preferably 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass. If it exceeds 20 parts by mass, the liquid viscosity may become too high and a film may not be uniformly formed on the particle surface of the lithium transition metal composite oxide. On the other hand, if it is less than 0.2 parts by mass, the effect of the coating film may be diminished. In addition, it is not economical because it takes a long time to concentrate and dry the solvent.

The precursor fine particles (hydrolysis products) in the film forming agent preferably have a central particle size of 100 nm or less as measured by a dynamic light scattering method. Since the film-forming agent obtained in this step is obtained through partial hydrolysis, the individual precursor fine particles are fine, and the precursor fine particles are less likely to aggregate with each other. In general, since the dynamic light scattering method measures the particle size including the aggregated form of the fine particles, the dynamic light is measured from the measurement value by a transmission electron microscope or the like for measuring the particle size of each precursor fine particle in the coating film. The value measured by the scattering method is smaller. The precursor fine particles produced by the production method of the present embodiment preferably have little aggregation from the viewpoint of forming a uniform oxide film, and the central particle size measured by the dynamic light scattering method is also the individual precursor fine particles. It is preferable that the particle size is close to that obtained by measuring with a method for measuring, for example, a transmission electron microscope or the like. Specifically, the central particle size measured by the dynamic light scattering method is more preferably 50 nm or less, and further preferably 0.1 nm or more and 10 nm or less. The central particle size of the precursor fine particles can be controlled within the above range by adjusting the type and mixing ratio of each component in the mixed solution and the heating conditions of the mixed solution and the undiluted solution.

The pH of the film-forming agent is preferably alkaline, more preferably pH 8 or higher and pH 11 or lower. Since the PH of the film-forming agent is alkaline, the elution of lithium from the composite oxide particles is alleviated during the mixing step, and an oxide film is formed on the particle surface without deteriorating the lithium transition metal composite oxide particles. Can be formed. The pH of the film-forming agent can be controlled within the above range by appropriately adjusting the type and mixing ratio of each component in the mixed solution or the undiluted solution, the heating conditions of the mixed solution, and the like.

Unlike the dispersion liquid having many coarse-grained particles, the film-forming agent obtained in this step can form a film having dense precursor fine particles on the surface of the lithium transition metal composite oxide particles with good adhesion. .. In addition, since at least some of the organic groups are hydrolyzed in this film and it is not a complete organic film, the influence of decomposition products during heat treatment and the problem of organic residue are eliminated, and it is unlikely to cause deterioration of battery characteristics. There are advantages. Further, the method for producing the film forming agent and the method for using the film forming agent are simple, and the cost can be reduced.

[Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary batteries]
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, also referred to as “positive electrode active material”) according to the present embodiment is as follows: 1) The above film-forming agent and lithium transition metal composite oxide particles are mixed. A mixing step of obtaining a mixture, a drying step of reducing the solvent (including water and an organic solvent) in the mixture and drying it, and 3) a heat treatment of the mixture after the drying step to heat the lithium transition metal composite oxide particles. It can include a heat treatment step of obtaining a positive electrode active material having an oxide film formed on the surface. The positive electrode active material obtained by this production method forms an oxide film that suppresses contact with water on at least a part of the particle surface, and has excellent water resistance.

The conventional method of coating a lithium transition metal composite oxide on a particle surface using a metal alkoxide has a problem that the water introduced to hydrolyze the metal alkoxide elutes lithium ions from the particle surface. In addition, it took a long time (several hours) to form a film due to the bonding of hydroxyl groups in the metal alkoxide, and then drying was also required. These long-time coating and drying steps not only cause deterioration of battery characteristics, but also cause problems in terms of cost due to reduction in productivity.

On the other hand, in the mixing and drying steps of the production method of the present embodiment, it is considered that the elution of lithium ions from the particle surface due to the moisture contained in the solvent hardly occurs. The reason for this is unknown, but the liberated chelating agent contained in the film-forming agent acts on the lithium on the particle surface during the mixing and drying steps, so that the lithium transition metal composite oxide particles themselves are also chelated. It is presumed that it is stable against water. The reason why the elution of lithium ions is suppressed is not limited to this.

In addition, 1) the time for the lithium transition metal composite oxide particles to come into contact with water is short because each step is a short-time treatment, 2) the film-forming agent used is alkaline, and 3) the organic group-containing metal. By hydrolyzing the compound, it becomes precursor fine particles having many hydroxyl groups, which are quickly adsorbed on the particle surface. It is considered that the elution of lithium ions is suppressed because of the fact that it can be treated.
Hereinafter, each step will be described in detail.

(Mixing process)
The mixing step is a step of mixing the film forming agent and the lithium transition metal composite oxide particles to obtain a mixture. The method for producing a positive electrode active material of the present embodiment can be applied to almost all positive electrode active materials. Therefore, the lithium transition metal composite oxide particles are not particularly limited, and composite oxide particles containing tyrium and a transition metal are used, for example, lithium nickel composite oxide, lithium cobalt composite oxide, and lithium nickel cobalt manganese. Examples thereof include particles made of a composite oxide, a lithium manganese composite oxide, and the like.

As the lithium transition metal double composite oxide particles, those represented by the following general formula (1) are preferably used from the viewpoint of improving the battery characteristics.
General formula: Li _a Ni _1-b M ¹ _b O ₂ ... (1)
(In the formula, M ¹ represents one or more elements selected from transition metal elements other than Ni, Group 2 elements, or Group 13 elements, 0.95 ≦ a ≦ 1.20, 0 ≦ b ≦ 0. .5.)

The lithium transition metal double composite oxide particles have high sensitivity to moisture and have the property that lithium is easily eluted. Usually, a film-forming agent that mainly uses water as a solvent is in a state in which Li, which is an alkaline component, is eluted from the surface of the composite oxide particles and is easily deteriorated. However, the film-forming agent according to the present embodiment can form a film without deteriorating the lithium transition metal double composite oxide particles. It is considered that this is because the inclusion of the chelating agent in the film forming agent alleviates the elution of lithium due to the influence of chelation on the particle surface.

The average particle size of the lithium transition metal composite oxide particles is not particularly limited, and may be the same particle size as the positive electrode active material to be finally obtained, and is preferably 3 μm or more and 25 μm or less, for example. More preferably, it is 3 μm or more and 15 μm or less. Since the positive electrode active material obtained by the production method of the embodiment can reduce the thickness of the oxide film, its particle structure and particle size distribution are almost the same as those of the lithium transition metal composite oxide particles used as a raw material. Can be maintained at. The average particle size is a volume-based median diameter (D50), and is measured by a particle size distribution measuring device by a laser diffraction / scattering method. The specific surface area of the lithium transition metal composite oxide particles is not particularly limited, and is preferably 0.1 m ² / g or more, 1.8 m ² / g or less, and more preferably 0.3 m ² / g or more. It can be 1.2 m ² / g or less.

The minimum amount of the film-forming agent to be mixed with the lithium transition metal composite oxide particles is such that the film-forming agent is adsorbed and permeated over the entire surface of the composite oxide particles, and is required to be on the surface of the composite oxide particles. It is preferable to contain a sufficient amount of precursor fine particles to be deposited. For example, the amount of the film-forming agent is preferably diluted with water so as to be 5 parts by mass or more with respect to 100 parts by mass of the lithium transition metal composite oxide particles used for mixing, and more preferably 10 to 50 parts by mass. .. On the other hand, if the amount of water added is too large, problems of drying and wettability and deterioration of the composite oxide particles due to water may occur.

The content of the precursor fine particles contained in the mixture is 0.1 to 10 parts by mass with respect to 100 parts by mass of the lithium transition metal composite oxide particles in terms of the amount of the metal compound having a hydrolyzable organic group added. Preferably, 1 part by mass to 4 parts by mass is more preferable. By setting the amount of the metal compound having a hydrolyzable organic group to 0.1 to 10 parts by mass, a sufficient amount of oxide fine particles are formed in the coating film, and the thickness of the coating film is formed more uniformly. can.

Since the amount of metal elements in the precursor fine particles contained in the mixture is maintained even after the heat treatment step described later, the total content of the metal elements contained in the mixture is 0. It is preferable to mix them so as to be 2 to 0.8% by mass.

The amount of water contained in the mixture is preferably 2 to 30 parts by mass, more preferably 4 to 25 parts by mass, based on 100 parts by mass of the lithium transition metal composite oxide particles. By setting the water content within the above range, the viscosity when the film-forming agent is mixed with the composite oxide particles can be made suitable for mixing, and the uniformity of each component can be improved to improve the uniformity of the composite oxide particles. A more uniform film can be formed on the surface. Further, the amount of the solvent (organic solvent and water) contained in the film forming agent is smaller than that of a general surface treatment composition, and drying in a subsequent step can be easily performed. If the amount of water is less than 2 parts by mass, there may be a problem that the mixing becomes insufficient. On the other hand, if it exceeds 20 parts by mass, it takes a long time to concentrate and dry the solvent, which is not economical. Further, since the components forming a film such as the precursor fine particles released during drying remain in the supernatant, there may be a problem that they remain as a high-concentration residue on the surface of the mixture after drying.

The mixing method is not particularly limited as long as it is a method of uniformly depositing (coating) the precursor fine particles on the surface of the composite oxide particles. Particles can be mixed. The kneading mixer can uniformly mix the mixture by applying an appropriate shearing force to the mixture, and the mixing can be performed in a short time, for example, about 1 to 5 minutes. Mixing for a short time with a rotation / revolution type kneading mixer can suppress damage to the surface of the composite oxide particles.

If a device such as a bead mill, a ball mill, a rod mill, a homogenizer, or the like in which a large force is directly applied to the composite oxide particles is used, the composite oxide particles are crushed or the particle surface is severely damaged. Lithium ions may be eluted from the particle surface. Therefore, when using these devices, it is preferable to adjust the mixing conditions so that a large force is not directly applied to the composite oxide particles.

The viscosity of the mixture is preferably 600 to 1100 mPa · s, more preferably 700 to 1000 mPa · s. By adjusting to such a viscosity, mixing becomes easy, the uniformity of each component can be improved, and a more uniform film can be formed on the surface of the composite oxide particles.

It is also possible to add a small amount of water-soluble glycols to the mixture. The addition of the water-soluble glycol can improve the uniformity of the film and avoid the occurrence of film cracking and peeling that occur during drying. Of these, water-soluble glycols having a slow drying rate are preferable, and specifically, the same water-soluble glycols as described in the above-mentioned film forming agent synthesis step section can be used.

(Drying process)
After mixing the film-forming agent and the lithium transition metal composite oxide particles, the solvent (water and organic solvent) in the mixture is evaporated to dry the mixture. In the process of this drying, the precursor fine particles in the film-forming agent are adsorbed and bonded to the surface of the lithium transition metal composite oxide particles to form a film.

For example, in the drying of a mixture obtained by a kneading mixer, if the solvent is rapidly volatilized at once, a large amount of liquid remains, so that agglutination between particles tends to occur at the same time as drying. In order to suppress this, it is preferable to evaporate the solvent slowly so as not to cause adhesion between the particles. Since the evaporation rate strongly depends on the temperature, it is effective to gradually expose it to a high temperature from room temperature. The rate of temperature rise during drying can be, for example, about 2 to 30 ° C./min. Further, the mixture may be dried as long as a film is formed on the surface of the particles and heat treatment can be performed in a subsequent step without completely evaporating the solvent. However, in order to suppress aggregation between the particles, the particles are dried. It is preferable to remove or evaporate the solvent to the extent that adhesion does not occur.

The drying temperature is preferably 70 ° C. or higher and 200 ° C. or lower, and preferably 70 ° C. or higher and 150 ° C. or lower. Since the film-forming agent of the present embodiment mainly uses an aqueous solvent, the drying temperature can be set to be slightly higher. If the drying temperature is less than 70 ° C., it takes a long time to dry, which may reduce productivity. On the other hand, when the drying temperature exceeds 200 ° C., the composite oxide particles tend to deteriorate. The drying time may be such that the solvent does not evaporate and adhesion between the particles does not occur, and is preferably 1 hour or more and 5 hours or less. If it is less than 1 hour, drying may be insufficient, and if it exceeds 5 hours, the productivity will decrease.

By drying within the above temperature range, the solvent and chelating agent remaining in the film are volatilized and decomposed, so that the film is mineralized and becomes a state close to an oxide. The dry atmosphere at this time is not particularly limited because the temperature is low, but it is preferable to use an air atmosphere from the viewpoint of ease of handling and cost. If more complete drying is required, it can be performed in a vacuum atmosphere.

(Heat treatment process)
The heat treatment step is a step of heat-treating the mixture after the mixing step to obtain a positive electrode active material having an oxide film formed on the surface of the lithium transition metal composite oxide particles. By this step, a positive electrode active material in which the oxide film is not peeled off even by kneading at the time of manufacturing the battery can be obtained.

The heat treatment temperature is higher than the drying temperature. Specifically, it is preferably in the range of 80 to 600 ° C, more preferably in the range of 150 to 600 ° C, and even more preferably in the range of 200 to 400 ° C. As a result, the coating film is fixed to the surface of the lithium transition metal composite oxide particles, and unnecessary components such as an organic solvent remaining in the coating film are removed to generate gas from the coating layer when used as an active material for a battery. It can be suppressed. If the heat treatment temperature is less than 80 ° C., an unnecessary organic solvent remains in the membrane, and gas generation may become a problem when charging / discharging after the battery cell. Further, when the heat treatment temperature exceeds 600 ° C., the coating film and the particles may react at the interface, and the battery characteristics of the positive electrode active material may deteriorate. Since the coating film is completely mineralized by the heat treatment, there is almost no heat loss when the obtained positive electrode active material is heated, and the amount is at most 3% or less.

The heat treatment time is preferably 0.5 to 10 hours, more preferably 1 to 5 hours. As a result, it is possible to sufficiently adhere to the surface of the lithium transition metal composite oxide particles and remove unnecessary organic components. If the heat treatment time is less than 0.5 hours, organic components may remain. On the other hand, if it exceeds 10 hours, the coating film and the particles may react at the interface, and the characteristics of the positive electrode active material may deteriorate.

The atmosphere during the heat treatment is selected from an oxygen-containing atmosphere, an inert atmosphere, and a vacuum atmosphere, but when the temperature exceeds 300 ° C., the treatment is performed in an oxygen atmosphere, and the surface of the lithium transition metal composite oxide particles is not reduced. It is preferable to do so.

[Cathode active material for non-aqueous electrolyte secondary batteries]
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present embodiment (hereinafter, simply referred to as “positive electrode active material”) is composed of lithium transition metal composite oxide particles and an oxide film covering at least a part of the particle surface. The average particle size D50 obtained by the above-mentioned production method and measured by the laser diffraction scattering method is 3 to 25 μm, and the oxide film is made of one or more oxides selected from zirconium, titanium, and aluminum. It is formed of fine particles, and the average particle size of the fine particles is 0.1 to 10 nm.

The lithium transition metal composite oxide particles are not particularly limited as long as they are composite oxide fine particles containing lithium and a transition metal (for example, nickel, cobalt, manganese, etc.), but are preferably lithium nickel composite oxides (for example, LiNiO). ₂ , LiNiCoAlO ₂ ), lithium cobalt composite oxide (eg LiCoO ₂ ), lithium manganese composite oxide (eg LiMn ₂ O ₄ ), or lithium nickel cobalt manganese composite oxide (eg LiNi _1/3 Co _{1) It is} a ternary lithium-containing composite oxide such as / 3 Mn _1/3 O _2). In particular, since the lithium nickel composite oxide having a high composition ratio of nickel (Ni) has a high battery capacity, it is preferable to use the particles represented by the following general formula (1), and the particles represented by the following general formula (2) are used. It is more preferable to do so.
General formula: Li _a Ni _1-b M ¹ _b O ₂ ... (1)
(In the formula, M ¹ represents at least one element selected from a transition metal element other than Ni, a group 2 element, or a group 13 element, and 0.95 ≦ a ≦ 1.20, 0 ≦ b ≦ 0. 5.)
General formula: Li _t Ni _1-x-y Co _x M ² _y O ₂ ... (2)
(In the formula, M ² represents at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, and 0.95 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15)

In the above formula (2), M ² preferably contains at least Al from the viewpoint of increasing the capacity of the positive electrode active material and thermal stability.

In the above general formulas (1) and (2), when Li is excessive (1.01 ≦ a ≦ 1.10) in order to obtain high capacity and excellent cycle characteristics, the sensitivity to water is particularly high, and Li Has the property of being easily eluted. In the production method of the present embodiment, since the film forming treatment is performed with an aqueous solvent, there is a concern that Li, which is an alkaline component, is eluted from the surface of the composite oxide particles and deteriorates. However, the pH of the film-forming agent indicates the alkaline side, and the Li elution is alleviated by the action of the chelating agent, and excess Li or the eluted Li reacts with a part of the film-forming agent during the heat treatment to form the Li compound phase. By forming it, it is possible to achieve both high battery characteristics and water resistance.

The powder characteristics of the positive electrode active material may be selected according to the characteristics required for the target positive electrode active material. For example, the average particle size is preferably 3 μm or more and 25 μm or less, and 3 μm or more and 15 μm or less. Is more preferable. By setting the average particle size within the above range, high battery capacity and fillability can be obtained. Here, the average particle size is measured by a particle size distribution measuring device based on the laser diffraction / scattering method in the same manner as the above-mentioned lithium transition metal composite oxide particles.

The positive electrode active material of the present embodiment has an oxide film formed of fine particles of one or more oxides selected from zirconium, titanium, and aluminum on the surface of the lithium transition metal composite oxide particles. When preparing a paste-like composition for forming a positive electrode mixture layer using an active material, it is possible to suppress elution of lithium ions from the positive electrode active material into a solvent containing water. As a result, the paste-like composition itself does not become strongly alkaline, and gelation of the paste-like composition can be suppressed. In addition, gelation of the paste-like composition due to the inflow of moisture from the outside air when working in a high humidity place is also suppressed.

Further, the oxide film suppresses the water absorption of the lithium transition metal composite oxide particles, and makes it possible to maintain the battery performance as the positive electrode active material. Further, in the secondary battery using this positive electrode active material, the influence of the decomposition products and water of the electrolytic solution generated during charging and discharging is suppressed by the oxide film, and the cycle characteristics can be improved.

The total content of the oxide fine particles is preferably 0.2 to 0.8% by mass, more preferably 0.2 to 0.6% by mass, still more preferably, with respect to 100% by mass of the entire positive electrode active material. It is 0.25 to 0.45% by mass. When the content of the oxide fine particles is in the above range, lithium elution and water absorption can be suppressed while maintaining high battery characteristics by making sufficient contact between the positive electrode active material and the electrolytic solution. When the content is less than 0.2% by mass, the coating film becomes thin, and the effect of suppressing lithium elution and water absorption may not be sufficiently obtained. On the other hand, if the content exceeds 0.8% by mass, the coating film becomes thick and the contact between the positive electrode active material and the electrolytic solution decreases, so that high battery characteristics may not be obtained.

The fine particles of the oxide preferably have an average particle size D50 measured by observation with a transmission electron microscope (TEM) of 0.1 nm or more and 10 nm or less. By making the oxide fine particles finer, it is possible to protect the lithium transition metal composite oxide particles even if the coating film is thinned, and even a small amount that does not adversely affect the battery characteristics is as described above. The effect is obtained. Further, from the viewpoint of achieving both suppression of deterioration of battery characteristics and suppression of lithium elution more highly, the thickness of the oxide film is preferably uniform, for example, the film thickness is preferably 5 nm or more and 100 nm or less. , More preferably 5 nm or more and 50 nm or less, and further preferably 5 nm or more and 30 nm or less. The oxide film can be formed into an arbitrary film thickness by adjusting the mixing amount of the film forming agent.

Since the oxide film is formed of fine particles of metal oxide, when the secondary battery is manufactured, the electrolytic solution can permeate the film and come into contact with the lithium transition metal composite oxide particles, but contact with the electrolytic solution. The coating is preferably formed discontinuously on the surface of the particles, and an oxide coating is formed from the viewpoint of suppressing deterioration of battery characteristics by contacting with the electrolytic solution. It is preferable that the non-existing portion is dispersed on the surface of the particles.

As the positive electrode active material of the present embodiment, it is preferable that the pH of the slurry 60 minutes after adding 1 g of the positive electrode active material to 50 ml of pure water at 24 ° C. is 11 or less. By setting the pH to 11 or less, the gelation suppressing effect of the paste-like composition for forming the positive electrode mixture layer can be improved.

The positive electrode active material of the present embodiment preferably has a mass increase rate of 2.0% or less after being exposed to a constant temperature and humidity chamber at 30 ° C. to 70% RH for 7 days. The mass increase is due to moisture absorption and chloride chloride, and the mass increase of 2.0% or less means that the water resistance is high and the deterioration of the positive electrode active material and the gelation of the paste-like composition are suppressed. show.

When the positive electrode active material of the present embodiment is used for the positive electrode of a non-aqueous electrolyte secondary battery, it has a high capacity and a high output. The non-aqueous electrolyte secondary battery obtained in a particularly preferable embodiment has a high initial discharge capacity of 160 mAh / g or more when used as a positive electrode of a 2032 type coin battery, and 180 mAh / g or more under more optimum conditions, and a low positive electrode. Resistance is obtained. In addition, it has high thermal stability and is excellent in safety.

[Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery embodiment of the present embodiment will be described in detail for each component. The non-aqueous electrolyte secondary battery of the present embodiment can be composed of the same components as a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, and the above positive electrode active material is used as the positive electrode. It was used. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is implemented in various modifications and improvements based on the knowledge of those skilled in the art, including the following embodiments. can do. Further, the non-aqueous electrolyte secondary battery of the present invention is not particularly limited in its use.

(Positive electrode)
The positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described. The powdered positive electrode active material of the present invention is mixed with a conductive material and a binder, and if necessary, activated carbon, a solvent for viscosity adjustment, etc. is added, and the mixture is kneaded to obtain a positive electrode mixture paste. To make. The performance of the lithium secondary battery can be controlled by appropriately adjusting the mixing ratio of each of the positive electrode mixture.

The content of each component of the positive electrode mixture is not particularly limited and may be the same as that of the positive electrode of a known lithium secondary battery. For example, the total mass of the solid content of the positive electrode mixture excluding the solvent. When is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass, the content of the conductive material is 1 to 20% by mass, and the content of the binder is 1 to 20% by mass, respectively. be able to.

The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like in order to increase the electrode density. In this way, a sheet-shaped positive electrode can be produced. The sheet-shaped positive electrode can be cut into an appropriate size according to the target battery and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the above-exemplified one, and other methods may be used.

In producing the positive electrode, as the conductive agent, for example, a carbon black material such as graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, Ketjen black (trademark), or the like can be used.

The binder serves as a binder that holds the active material particles together. For example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluororubber, styrene butadiene, cellulosic resin, polyacrylic acid, etc. Can be used. If necessary, the positive electrode active material, the conductive material, and the activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone, dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, hexamethylphosphoamide and the like can be used. .. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(Negative electrode)
For the negative electrode, metallic lithium, lithium alloy, etc., or a negative electrode mixture that is made into a paste by mixing a binder with a negative electrode active material that can occlude and desorb lithium ions and adding an appropriate solvent, is made of copper, etc. It can be applied to the surface of a metal foil current collector, dried, and if necessary, compressed to increase the electrode density.

Examples of the negative electrode active material include calcined organic compounds such as natural graphite, artificial graphite, and phenolic resin, powdered carbon substances such as coke, and oxides such as lithium-titanium oxide (Li ₄ Ti ₅ O ₁₂ ). Materials can be used. In this case, as the negative electrode binder, a fluororesin such as polyvinylidene fluoride can be used as in the positive electrode, and as a solvent for dispersing these active substances and the binder, N-methyl-2-pyrrolidone or the like can be used. An organic solvent can be used.

(Separator)
A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode to retain the electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of minute holes, can be used.

(Non-aqueous electrolyte solution)
The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2-. One selected from ether compounds such as methyl tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, etc., and a composite salt thereof can be used.

Further, the non-aqueous electrolyte solution may contain a radical catching agent, a surfactant, a flame retardant and the like.

(Battery shape and configuration)
The shape of the lithium secondary battery according to the present invention, which is composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte solution described above, can be various, such as a cylindrical type and a laminated type.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolytic solution. The positive electrode current collector and the positive electrode terminal that communicates with the outside, and the negative electrode current collector and the negative electrode terminal that communicates with the outside are connected by using a current collector lead or the like. The battery can be completed by sealing the above configuration in a battery case.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. Each evaluation in the examples of the present invention was carried out by the following method.

1. 1. Various physical characteristics of the film-forming agent and the positive electrode material (1) Measurement of the particle size of the precursor fine particles and the positive electrode active material in the film-forming agent:
The average particle size (D50) of the precursor fine particles was measured using a particle size distribution meter (Nanotrack WAVE, manufactured by Nikkiso Co., Ltd.). The average particle size (D50) of the lithium transition metal composite oxide powder and the active material of the positive electrode material was measured using a particle size distribution meter (Microtrac MT3300, manufactured by Nikkiso Co., Ltd.).
(2) Evaluation of water resistance and moisture resistance of the positive electrode active material The water resistance was evaluated by adding 1 G of the positive electrode active material to 50 ml of pure water at 24 ° C., stirring the mixture, and measuring the pH after 60 minutes. The moisture resistance was evaluated by the mass increase rate before and after the exposure of the positive electrode active material in a constant temperature and humidity chamber at 30 ° C. to 70% RH for 7 days.
The water resistance was evaluated by adding 1 g of the positive electrode active material to 50 ml of pure water at 24 ° C., stirring the mixture, and measuring the pH after 60 minutes. The moisture resistance was evaluated by the mass increase rate before and after the exposure of the positive electrode active material in a constant temperature and humidity chamber at 30 ° C. to 70% RH for 7 days.
(3) Gelation evaluation In the gelation evaluation, 9.5 g of positive electrode active material, 0.5 g of vinylidene fluoride (PVDF) as a binder, 5.5 g of N-methyl-2-pyrrolidinone (NMP) as a solvent, and 0 water. .2 g was made into a slurry by a self-conversion kneading machine, and then statically stored at 24 ° C. for 4 days, and the gelation state was confirmed by visual observation.

2. Battery manufacturing and evaluation of battery characteristics (battery manufacturing)
The 2032 type coin battery 1 (hereinafter referred to as a coin type battery) shown in FIG. 1 was used for the evaluation of the positive electrode active material.
As shown in FIG. 1, the coin-type battery 1 is composed of a case 2 and an electrode 3 housed in the case 2. The case 2 has a positive electrode can 2A that is hollow and has one end opened, and a negative electrode can 2b that is arranged in the opening of the positive electrode can 2a. When the negative electrode can 2b is arranged in the opening of the positive electrode can 2a, , A space for accommodating the electrode 3 is formed between the negative electrode can 2b and the positive electrode can 2a.

The electrode 3 is composed of a positive electrode 3a, a separator 3c, and a negative electrode 3b, and is laminated so as to be arranged in this order. The positive electrode 3a contacts the inner surface of the positive electrode can 2a, and the negative electrode 3b contacts the inner surface of the negative electrode can 2b. It is housed in the case 2. The case 2 is provided with a gasket 2c, and the gasket 2c fixes the relative movement between the positive electrode can 2a and the negative electrode can 2b so as to maintain a non-contact state. Further, the gasket 2c also has a function of sealing the gap between the positive electrode can 2a and the negative electrode can 2b to seal the inside and the outside of the case 2 in an airtight and liquid-tight manner.

The coin-type battery 1 was manufactured as follows.
First, 52.5 mg of the positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) are mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. , Positive electrode 3a was prepared. The prepared positive electrode 3a was dried in a vacuum dryer at 120 ° C. for 12 hours. Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolytic solution, the above-mentioned coin-type battery 1 was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C. For the negative electrode 3b, a graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and a negative electrode sheet coated with polyvinylidene fluoride on a copper foil were used. A polyethylene porous membrane having a film thickness of 25 μm was used for the separator 3c. As the electrolytic solution, an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using _{1M LiCLO 4 as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.}

(Evaluation of battery characteristics)
The initial discharge capacity and positive electrode resistance indicating the performance of the manufactured coin-type battery 1 were evaluated as follows.
The initial discharge capacity is the cutoff voltage 4 ^{with the current density for the positive electrode set to 0.1 mA / cm 2} after the open circuit voltage OCV (OPEN CIRCUIT VOLTAGE) stabilizes after being left for about 24 hours after the coin-type battery 1 is manufactured. The initial discharge capacity was defined as the capacity when the battery was charged to 3 V, paused for 1 hour, and then discharged to a cutoff voltage of 3.0 V.

The positive electrode resistance was evaluated by the AC impedance method. That is, the coin-type battery 1 was charged with a charging potential of 4.1 V and measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) to obtain a Nyquist plot. Since this Nyquist plot is expressed 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 this Nyquist plot, and the positive electrode resistance is performed. The value of was calculated. The positive electrode resistance was evaluated by a relative value using the positive electrode resistance of Comparative Example 1 as a reference value.

(Lithium Transition Metal Composite Compound LiNiCoAlO ₂ )
Lithium transition metal composite oxide powder obtained by a known technique was used as a positive electrode active material. That is, a lithium transition metal composite represented _{by Li 1.03} Ni _0.76 Co _0.14 Al _0.10 O ₂ is obtained by mixing and firing nickel oxide powder containing Ni as a main component and lithium hydroxide. Oxide powder was obtained. The average particle size of this lithium transition metal composite oxide powder was 11.3 μm, and the specific surface area was 0.41 m ² / g.

(Example 1)
(Preparation of film forming agent)
2.33 g of zirconium butoxide (manufactured by Kanto Chemical Co., Inc.) was added to 7 ml of 2-propanol in advance and stirred to prepare a solution (A). To a separate container, 0.44 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) was added to 3 ml of 2-propanol and stirred to prepare a solution (B). The solution (B) was put into the solution (A) and stirred and mixed to prepare a solution (C). The solution (C) was placed in a tightly closed container, heated at 80 ° C. for 1 hour with stirring, cooled and returned to room temperature to prepare a solution (D). 0.69 g of pure water was added to the solution (D), the amount of the solution was adjusted to 12 ml with 2-propanol, and then heated at 80 ° C. for 1 hour with stirring, cooled to return to room temperature, and partially hydrolyzed. A clear yellow solution (F) (stock solution) was prepared. The solution (F) did not change even after being left for 1 month. Further, 4 ml was separated from the above solution (F), 6 ml of pure water was mixed, and the mixture was stirred at room temperature for 5 minutes to obtain a film forming agent (G). Table 1 summarizes various physical characteristics of the film forming agent (G).

(Preparation of positive electrode active material)
40 g of the lithium transition metal composite compound powder was separately mixed with the entire amount of the film forming agent (G) for 1 minute using a self-revolving kneader (ARV-310LED manufactured by Shinky) to obtain a mixture. The viscosity of this mixture was 860 mPa · s. Then, it was dried at 80 ° C. for 3 hours in the air atmosphere and further dried at 110 ° C. for 1 hour in the air atmosphere. Further, heat treatment was performed by heating at 300 ° C. for 1 hour in a pure oxygen atmosphere to obtain a positive electrode active material. The obtained positive electrode active material was cross-sectioned with a cross section polisher (CP), and the oxide film was observed with a transmission electron microscope (TEM). As a result, the thickness of the film was uniform and the oxide fine particles of less than 10 nm were observed. It was confirmed that the portion formed from the above and not formed with a film was dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 2)
In the preparation of the film-forming agent, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that 0.2 g of polypropylene glycol was added to the solution (D). Table 1 summarizes various physical characteristics of the film forming agent (G). The viscosity of the mixture was 910 mPa · S.
When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 3)
In the preparation of the film-forming agent, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of acetylacetone added to the solution (B) was changed to 0.88 g. Table 1 summarizes various physical characteristics of the film forming agent (G). The viscosity of the mixture was 800 mPa · s.
When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 4)
In the preparation of the film-forming agent, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of acetylacetone added to the solution (B) was changed to 0.66 g. Table 1 summarizes various physical characteristics of the film forming agent (G). The viscosity of the mixture was 840 mPa · s.
When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 5)
In the preparation of the film-forming agent, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the amount of pure water added to the solution (D) was changed to 0.46 g. The viscosity of the mixture was 960 mPa · s. Table 1 summarizes various physical characteristics of the film forming agent (G).
When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 6)
In the preparation of the film-forming agent, the positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the heating of the solution (C) was changed at 70 ° C. for 0.5 hours. Table 1 summarizes various physical characteristics of the film forming agent (G). The viscosity of the mixture was 910 mPa · s.
When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 7)
In the preparation of the film-forming agent, the positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the heating of the solution (C) was changed at 90 ° C. for 0.5 hours. Table 1 summarizes various physical characteristics of the film forming agent (G). The viscosity of the mixture was 900 mPa · s.
When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Example 8)
(Preparation of film forming agent)
2.00 g of titanium isopropoxide (manufactured by Kanto Chemical Co., Inc.) was added to 7 ml of 2-propanol in advance and stirred to prepare a solution (A). A solution (B) was prepared by adding 1.00 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) to 3 ml of 2-propanol in a separate container and stirring. The solution (B) was put into the solution (A) and stirred and mixed to prepare a solution (C). The solution (C) was placed in a tightly closed container, heated at 80 ° C. for 1 hour with stirring, cooled and returned to room temperature to prepare a solution (D). 0.69 g of pure water is added to the solution (D), the amount of the solution is adjusted to 12 ml with 2-propanol, the mixture is heated at 80 ° C. for 1 hour with stirring, cooled to return to room temperature, and partially hydrolyzed. A transparent dark yellow solution (F) was prepared. The solution (F) did not change even after being left for 1 month. Further, 4 ml was separated from the above solution (F), and 6 ml of pure water was mixed to obtain a film forming agent (G). Table 1 summarizes various physical characteristics of the film forming agent (G).
(Preparation of positive electrode active material)
40 g of the lithium transition metal composite compound powder was separately mixed with the entire amount of the film forming agent (G) for 1 minute using a self-revolving kneader (ARV-310LED manufactured by Shinky) to obtain a mixture. The viscosity of this mixture was 780 mPa · s. Then, it was dried at 80 ° C. for 3 hours in the air atmosphere and further dried at 110 ° C. for 1 hour in the air atmosphere. Further, heat treatment was performed by heating at 300 ° C. for 1 hour in a pure oxygen atmosphere to obtain a positive electrode active material. When the obtained positive electrode active material was cross-sectionald with CP and the oxide film was observed with TEM, the thickness of the film was uniform, and it was formed from fine particles of oxide of less than 10 nm, and the film was not formed. Was confirmed to be dispersed on the surface of the lithium transition metal double composite oxide particles. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

(Comparative Example 1)
The lithium-nickel composite oxide powder used in Example 1 was evaluated as a positive electrode active material as it was without being treated. The evaluation results of the positive electrode active material are summarized in Table 2.

(Comparative Example 2)
(Preparation of film forming agent)
2.33 g of zirconium butoxide (manufactured by Kanto Chemical Co., Inc.) was added to 7 ml of 2-propanol in advance and stirred to prepare a solution (A). To a separate container, 0.1 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) was added to 3 ml of 2-propanol and stirred to prepare a solution (B). The solution (A) and the solution (B) were mixed to obtain a solution (C), and the amount of the solution was adjusted to 12 ml with 2-propanol.
(Preparation of positive electrode active material)
Immediately after 40 g of the lithium transition metal composite oxide powder was separately added and 4 ml of the above solution (C) and 6 ml of pure water were added, a white film covered the surface of the lithium transition metal composite oxide powder, so that the subsequent steps were stopped. When the white part was taken out and EDS analyzed, a high concentration of zirconium was detected. It was considered that zirconium butoxide was rapidly hydrolyzed and became cloudy.

(Comparative Example 3)
(Preparation of film forming agent)
2.33 g of zirconium butoxide (manufactured by Kanto Chemical Co., Inc.) was added to 7 ml of 2-propanol in advance and stirred to prepare a solution (A). To a separate container, 0.1 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) was added to 3 ml of 2-propanol and stirred to prepare a solution (B). The solution (B) was put into the solution (A) and stirred and mixed to prepare a solution (C). Immediately after adding 1.00 g of pure water to the solution (C), a cloudy liquid was obtained as in Comparative Example 2. After that, even if it was heated, it remained cloudy and did not become a transparent liquid, so the subsequent steps were stopped.

(Comparative Example 4)
(Preparation of film forming agent)
2.00 g of titanium isopropoxide (manufactured by Kanto Chemical Co., Inc.) was added to 7 ml of 2-propanol in advance and stirred to prepare a solution (A). To a separate container, 2.00 g of triethanolamine (manufactured by Kanto Chemical Co., Inc.) was added to 3 ml of 2-propanol and stirred to prepare a solution (B). The solution (B) was put into the solution (A) and stirred and mixed to prepare a solution (C). The solution (C) was placed in a tightly closed container and stirred at room temperature for 1 hour without heating to prepare a yellow solution (D). 1.00 g of pure water was added to the solution (D), the amount of the solution was adjusted to 12 ml with 2-propanol, and then the solution (F) was prepared by stirring. Further, 4 ml was separated from the above solution (F), and 6 ml of pure water was mixed to obtain a film forming agent (G). Table 1 summarizes various physical characteristics of the film forming agent (G).
(Preparation of positive electrode active material)
40 g of the lithium transition metal composite compound powder was separately mixed with the entire amount of the film forming agent (G) for 1 minute using a self-revolving kneader (ARV-310LED manufactured by Shinky) to obtain a mixture. The viscosity of the mixture was 770 mPa · s. The evaluation results of the obtained positive electrode active material are summarized in Table 2.

なお、表１の質量部は、加水分解性有機基を有する金属化合物（有機基含有金属化合物）の添加量１００質量部に対する、各成分の添加割合（質量部）を示す。

In addition, the mass part of Table 1 shows the addition ratio (mass part) of each component with respect to 100 mass parts of the addition amount of the metal compound (organic group-containing metal compound) having a hydrolyzable organic group.

According to the present invention, a positive electrode activity for a non-aqueous electrolyte secondary battery that has a high capacity and a high output and does not gel even if left at room temperature for a long time after preparation of a paste-like composition for forming a positive electrode active material layer. The substance is obtained. Such a cathode active material is suitable for an in-vehicle non-aqueous electrolyte secondary battery, which is required to have high capacity and high output, and further high productivity is required. Further, the obtained non-aqueous electrolyte secondary battery can be suitably used as a power source for a motor (motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

1: Coin-type battery 2: Case 2a: Positive electrode can 2b: Negative electrode can 2c: Gasket 3: Electrode 3a: Positive electrode 3b: Negative electrode 3c: Separator

Claims (15)

A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery in which an oxide film is formed on the surface of lithium transition metal composite oxide particles.
A mixed solution containing a metal compound having a hydrolyzable organic group, a chelating agent, and an organic solvent is heated to 50 to 100 ° C., and a part of the hydrolyzable organic group contained in the metal compound is used by the chelating agent. After chelation, water is mixed with the mixed solution to obtain a stock solution containing the precursor fine particles produced by partially hydrolyzing the metal compound, and a stock solution synthesis step.
By mixing water into the stock, said the precursor particles, and the chelating agent, and the organic solvent medium, and the film forming agent synthesized to obtain a film-forming agent comprising water,
A mixing step of mixing the film-forming agent and lithium transition metal composite oxide particles to obtain a mixture.
A drying step of drying the mixture to reduce the organic solvent and water in the mixture and forming a film on the surface of the lithium transition metal composite oxide particles in which the precursor fine particles are adsorbed and bonded.
By heat-treating the mixture after the drying step to fix the coating film on the surface of the lithium transition metal composite oxide particles and removing the organic component contained in the coating film, oxidation composed of fine particles of the metal oxide is performed. A heat treatment process for obtaining a positive electrode active material on which a material film is formed, and
Equipped with
In the positive electrode active material, portions where the oxide film is not formed are dispersed on the surface of the lithium transition metal composite oxide particles.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to claim 1, wherein in the stock solution synthesis step, water is mixed with the mixed liquid and then the liquid temperature is maintained at 20 to 90 ° C. to obtain the stock solution. A method for producing a positive electrode active material. The positive electrode activity for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the metal compound having a hydrolyzable organic group comprises one or more selected from alkoxides of zirconium, titanium, and aluminum. Method of manufacturing the substance. The metal compound having a hydrolyzable organic group is characterized by comprising one or more selected from zirconium butoxide, titanium isopropoxide, titanium butoxide, aluminum isopropoxide, aluminum diisopropoxide and aluminum butoxide. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the chelating agent comprises at least one selected from an aminocarboxylic acid salt and a salt thereof, and a diketone and a salt thereof. Manufacturing method. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the chelating agent is composed of acetylacetone. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the organic solvent comprises one or more selected from ethanol, 2-propanol and 1-butanol. Production method. The non-aqueous system according to any one of claims 1 to 7, wherein the particle size of the hydrolysis product contained in the film-forming agent has a central particle size of 100 nm or less measured by a dynamic light scattering method. A method for producing a positive electrode active material for an electrolyte secondary battery. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 8, wherein the pH of the film-forming agent is 8 to 11. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein in the mixing step, mixing is performed using a rotation / revolution type kneading mixer. The production of the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10, wherein one or more selected from polyethylene glycol, polypropylene glycol and hexylene glycol are added to the mixture before the drying step. Method. The method according to claim 10 or 11, wherein in the heat treatment step, the heat treatment is performed by controlling the heat treatment temperature in the range of 80 to 400 ° C. in an atmosphere selected from an oxygen-containing atmosphere, an inert atmosphere, and a vacuum atmosphere. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. A positive electrode active material for a non-aqueous electrolyte secondary battery having lithium transition metal composite oxide particles and an oxide film covering the surface of the particles.
The average particle size D50 measured by the laser diffraction / scattering method is 3 to 25 μm.
The oxide film is formed of fine particles of one or more oxides selected from zirconium, titanium, and aluminum, and the average particle size D50 of the fine particles is 0.1 to 10 nm.
The fine particles are contained in an amount of 0.2 to 0.6% by mass based on the entire positive electrode active material.
The lithium transition metal composite oxide particles are represented by the following general formula (1).
A cathode active material for a non-aqueous electrolyte secondary battery, characterized in that portions in which the oxide film is not formed are dispersed on the surface of the lithium transition metal composite oxide particles.
General formula: Li _a Ni _1-b M1 _b O ₂ ... (1)
(In the formula, M1 represents one or more elements selected from a transition metal element other than Ni, a group 2 element, or a group 13 element, and 0.95 ≦ a ≦ 1.20, 0 ≦ b ≦ 0. 5.) 60 minutes after adding 1 g of the positive electrode active material to 50 ml of pure water at 24 ° C., the pH of the slurry is 11 or less, and the positive electrode active material is exposed to a constant temperature and humidity chamber at 30 ° C. to 70% RH for 7 days. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 13, wherein the mass increase rate after exposure is 2.0% or less. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a positive electrode including the positive electrode active material according to claim 13 or 14.

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