JP2017224590A - Method for producing positive electrode active material for lithium secondary battery and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a positive electrode active material for a lithium secondary battery having an aluminum oxide coating film which has less damage to an active material by a simple method which can be adopted industrially and can also reduce mixing of impurities and to further provide a lithium secondary battery excellent in cycle characteristics by using the positive electrode active material produced by the method of the present invention.SOLUTION: The method for producing a positive electrode active material for a lithium secondary battery includes: causing an alkylaluminum partial hydrolyzate to act on a composite oxide particle of lithium and a transition metal; and calcining at a temperature condition of 50°C to 1000°C. The alkylaluminum partial hydrolyzate of 0.01 to 10 parts by mass in terms of alumina is caused to act on 100 parts by mass of the positive electrode active material.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery and a lithium secondary battery using a positive electrode produced by the method. Specifically, using a specific alkylaluminum compound, a method for producing a positive electrode active material having an aluminum oxide coating with less physical damage to the positive electrode active material and reduced impurities, and lithium using a positive electrode produced by this method The present invention relates to a secondary battery.

  Lithium secondary batteries have high output density and high energy density, and are widely used as power sources for mobile phones, notebook computers, tablet computers, and the like. In particular, due to the high energy density and output density, its use as a power source for electric vehicles is expanding as well as consumer and small-sized applications. For these applications, a service life exceeding 10 years, which is the same as that of an internal combustion engine, is required (Non-Patent Document 1).

  Further, these lithium secondary batteries are required to have higher energy density such as reduction in battery size and extension of the cruising distance of electric vehicles. As a method for increasing the energy density, an active material having a large theoretical capacity or a method of charging / discharging at a higher voltage has been studied. When operated at a higher voltage than before, there has been a problem that the positive electrode has a strong oxidizing atmosphere, decomposition of the electrolyte progresses on the surface of the positive electrode, and the stability of the positive electrode itself decreases.

  For such a problem, it is known that the stability of the battery is improved by forming a metal oxide film on the surface of the positive electrode active material. For example, Patent Document 1 proposes a technique in which particles of a positive electrode active material are coated with a metal oxide by sputtering in order to suppress decomposition of the electrolytic solution on the surface of the positive electrode. Patent Documents 2 and 3 propose a technique in which ceramic particles such as alumina are directly attached to the surface of the positive electrode active material for the purpose of providing a lithium ion secondary battery having excellent cycle characteristics. Patent Document 4 discloses a method in which a colloid of aluminum hydroxide is produced in an aqueous solution of sodium aluminate or aluminum sulfate, a lithium cobalt composite oxide is dispersed in the aqueous colloid solution, and a coating layer is formed by adsorption. .

Japanese Patent Laid-Open No. 08-236114 JP 2010-140737 A Special table 2013-541129 gazette JP 2002-151077 A

Publisher of “Development of Lithium-ion Battery Active Material and Electrode Material Technology” Hiroshi Motoki, Science & Technology Co., Ltd. (issued January 30, 2014), p. 15

The method based on the sputtering method disclosed in Patent Document 1 is an extremely effective method for a flat surface where the object to be coated is smooth in a manufacturing process of a semiconductor or the like. However, this method is insufficient for forming a uniform coating on irregularly shaped particles such as a positive electrode active material.
The coating method using ceramic particles disclosed in Patent Documents 2 and 3 has an advantage that it can be easily controlled to an arbitrary composition by using the same metal oxide as the coating composition. However, since the powder particles are coated by friction between them, the active material may be greatly damaged, and the ceramic itself has a large particle size, so that it is difficult to make a thin film. In either case, the resulting coated active material has problems such as an increase in resistance on the surface of the active material.
The method of generating aluminum hydroxide colloid in an aqueous solution of sodium aluminate or aluminum sulfate disclosed in Patent Document 4 is difficult to eliminate sulfate ions and the like in the system, and remains as an impurity in the crystal structure. As a result, there was a problem of lowering battery performance.

  The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a means capable of providing a positive electrode active material for a lithium secondary battery that can provide a lithium secondary battery having excellent cycle characteristics, and more specifically, a lithium secondary battery. A method for producing a positive electrode active material for a secondary battery, which can be carried out relatively easily on an active material that is an irregularly shaped particle, is less likely to cause damage to the active material during implementation, and contains impurities. To provide a method with little or substantially no contamination of impurities. Furthermore, the subject of this invention is providing the lithium secondary battery excellent in cycling characteristics using the positive electrode active material for lithium secondary batteries provided by this invention.

  As a result of intensive studies to solve the above problems, the present inventors have developed a composite material obtained by allowing a relatively reactive alkylaluminum compound to act on a composite oxide particle of lithium and a transition metal. It has been found that the cycle characteristics of a non-aqueous lithium secondary battery are improved by using it as an active material, and the present invention has been completed.

That is, the present invention is as follows.
(1)
Partial hydrolysis of an alkylaluminum compound which is a dialkylaluminum, a trialkylaluminum or a mixture thereof (provided that the alkyl groups in the dialkylaluminum and the trialkylaluminum can be the same or different and have 1 to 8 carbon atoms) A step of forming a coating of the partial hydrolyzate on at least a part of the surface of the composite oxide of lithium and transition metal using the product, and firing the composite oxide formed with the coating of the partial hydrolyzate And a method for producing a positive electrode active material comprising a composite oxide having an aluminum oxide coating, comprising a step of forming a composite oxide having an aluminum oxide coating.

  Usually, a temperature of 600 ° C. or higher is required to produce alumina from aluminum hydroxide (including hydrate), but by using a partially hydrolyzed product of highly reactive alkylaluminum compound, 600 ° C. It is a surprising effect that the coating effect can be exhibited even at a temperature lower than ° C.

(2)
The said partial hydrolyzate is a manufacturing method as described in (1) used for coating | cover of complex oxide as a mixture with a nonaqueous solvent.

(3)
The production method according to (1) or (2), wherein the dialkylaluminum is an alkylaluminum compound represented by the following general formula (1).
(In the formula, R ¹ is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group, and X represents a halogen atom such as hydrogen, fluorine, chlorine, bromine or iodine.

(4)
The production method according to any one of (1) to (3), wherein the trialkylaluminum is an alkylaluminum compound represented by the following general formula (2).
(In the formula, R ² is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group.

(5)
The production method according to any one of (1) to (4), wherein the lithium-transition metal composite oxide includes a lithium transition metal composite oxide or a lithium-containing transition metal phosphate compound.
(6)
The composite oxide of lithium and transition metal is LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFeO ₂ , LiNi _0.5 Mn _1.5 O ₂ , LiNi _x Co _y Al _z O ₂ (x + y + z = 1), LiNi _x Co _y Mn _z O ₂ (x + y + z = 1), LiFePO ₄ , LiMnPO ₄ , or one or more composite oxides selected from the group consisting of LiCoPO ₄ are described in any one of (1) to (4) Manufacturing method.
(7)
The coating amount of the partial hydrolyzate on the composite oxide is 0.01 to 10 parts by mass in terms of alumina with respect to 100 parts by mass of the composite oxide, according to any one of (1) to (6). Production method.

(8)
The said baking is a manufacturing method in any one of (1)-(7) implemented at the temperature of the range of 50 to 1000 degreeC.

(9)
The manufacturing method in any one of (1)-(8) whose mass ratio of the complex oxide in the said positive electrode active material and an aluminum oxide film is the range of 100: 0.01-10.

(10)
The production method according to any one of (1) to (9), wherein the positive electrode active material is for a lithium secondary battery.

(11)
A positive electrode active material is manufactured by the method as described in (1)-(10), The positive electrode active material is obtained using the obtained positive electrode active material, The manufacturing method of a positive electrode.

(12)
The manufacturing method of a lithium secondary battery which manufactures a positive electrode by the method as described in (11), and manufactures a lithium secondary battery using the obtained positive electrode and negative electrode, a separator, and a non-aqueous electrolyte.
(13)
Partial hydrolysis of an alkylaluminum compound which is a dialkylaluminum, a trialkylaluminum or a mixture thereof (provided that the alkyl groups in the dialkylaluminum and the trialkylaluminum can be the same or different and have 1 to 8 carbon atoms) A composition for producing a positive electrode active material comprising a composite oxide having an aluminum oxide film.
(14)
The composition according to (13), wherein the partial hydrolyzate of the alkylaluminum compound is a mixture of compounds containing a structural unit represented by the following general formula (3).
(In the formula, R ³ is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group, m is an integer of 1-80.
(15)
The composition according to (13) or (14), further comprising one or more nonaqueous solvents.

  According to the method of the present invention, there is provided a method for producing a positive electrode active material for a lithium secondary battery having an aluminum coating that can be industrially adopted, has little damage to the active material, and can reduce contamination by impurities. can do. Furthermore, by using the positive electrode active material produced by the method of the present invention, a lithium secondary battery with significantly improved charge / discharge cycle life can be provided.

It is a schematic diagram which shows the battery of the coin cell used for Examples 1-24 and Comparative Examples 1-6. It is IR spectrum by the transmission method of what dried the triethylaluminum hydrolysis composition NMP solution prepared in the preparation example 1. FIG. It is IR spectrum by the transmission method of what dried the triisobutylaluminum hydrolysis composition NMP solution prepared in the preparation example 5. FIG. It is IR spectrum by the transmission method of what dried the trimethylaluminum hydrolysis composition toluene solution prepared in the preparation example 7. FIG.

The present invention uses a partial hydrolyzate of an alkylaluminum compound which is a dialkylaluminum, a trialkylaluminum or a mixture thereof, and coats the partial hydrolyzate on at least a part of the surface of the composite oxide of lithium and transition metal. And forming the composite oxide having an aluminum oxide film by firing the composite oxide having the partial hydrolyzate film formed thereon, and a composite oxide having an aluminum oxide film The present invention relates to a method for producing a positive electrode active material.
Furthermore, this invention relates to the composition for positive electrode active material manufacture which consists of complex oxide which has an aluminum oxide film containing the partial hydrolysis product of the alkylaluminum compound which is a dialkylaluminum, a trialkylaluminum, or those mixtures.

  The “partial hydrolyzate of alkyl aluminum compound” in the composition for producing a positive electrode active material is common to the “partial hydrolyzate of alkyl aluminum compound” in the method for producing a positive electrode active material. Furthermore, the “positive electrode active material comprising a composite oxide having an aluminum oxide film” in the composition for producing a positive electrode active material is the “positive electrode active material comprising a composite oxide having an aluminum oxide film” in the method for producing a positive electrode active material. Common.

The partial hydrolyzate of alkylaluminum used in the production method of the present invention is an alkylaluminum compound comprising a dialkylaluminum, a trialkylaluminum or a mixture thereof (provided that the alkyl group has 1 to 8 carbon atoms and is the same or different. May be hydrolyzed.
An example of the dialkylaluminum is an alkylaluminum compound represented by the following general formula (1).

(In the formula, R ¹ is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group, and X represents a halogen atom such as hydrogen, fluorine, chlorine, bromine or iodine.

  Examples of the compound represented by the general formula (1) include, for example, dimethylaluminum hydride, dimethylaluminum fluoride, dimethylaluminum chloride, dimethylaluminum bromide, dimethylaluminum iodide, diethylaluminum hydride, diethylaluminum fluoride, diethylaluminum. Chloride, diethylaluminum bromide, diethylaluminum iodide, di-n-propylaluminum hydride, di-n-propylaluminum fluoride, di-n-propylaluminum chloride, di-n-propylaluminum bromide, di-n-propylaluminum Iodide, diisopropylaluminum hydride, diisopropylaluminum fluoride, diisopropyl Luminium chloride, diisopropylaluminum bromide, diisopropylaluminum iodide, di-n-butylaluminum hydride, di-n-butylaluminum fluoride, di-n-butylaluminum chloride, di-n-butylaluminum bromide, di-n-butyl Aluminum iodide, diisobutylaluminum hydride, diisobutylaluminum fluoride, diisobutylaluminum chloride, diisobutylaluminum bromide, diisobutylaluminum iodide, di-t-butylaluminum hydride, di-t-butylaluminum fluoride, di-t-butylaluminum chloride , Di-t-butylaluminum bromide, di-t-butylaluminum iodide Di-n-pentylaluminum hydride, di-n-pentylaluminum fluoride, di-n-pentylaluminum chloride, di-n-pentylaluminum bromide, di-n-pentylaluminum iodide, di-n-hexylaluminum hydride, Di-n-hexyl aluminum fluoride, di-n-hexyl aluminum chloride, di-n-hexyl aluminum bromide, di-n-hexyl aluminum iodide, di-n-heptyl aluminum hydride, di-n-heptyl aluminum fluoride , Di-n-heptyl aluminum chloride, di-n-heptyl aluminum bromide, di-n-heptyl aluminum iodide, di-n-octyl aluminum hydride, di-n-octyl aluminum Examples thereof include nium fluoride, di-n-octyl aluminum chloride, di-n-octyl aluminum bromide, and di-n-octyl aluminum iodide.

An example of the trialkylaluminum is an alkylaluminum compound represented by the following general formula (2).
(In the formula, R ² is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group.

  Examples of the compound represented by the general formula (2) include, for example, trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-t-butyl. Aluminum, tri-n-pentyl aluminum, tri-n-hexyl aluminum, tri-n-heptyl aluminum, tri-n-octyl aluminum, and the like can be given.

  The partial hydrolysis of the alkylaluminum compound is carried out using water in such a range that the total amount of aluminum of the alkylaluminum compound is not hydrolyzed (the bond with alkyl is replaced by the bond with oxygen). More specifically, the molar ratio with respect to the alkylaluminum compound can be performed, for example, using water in the range of 0.5 to 1.3. Water can be used alone or as a solution containing water. When the molar ratio of water to the alkylaluminum compound is less than 0.5, a step of further oxidizing with oxygen or water may be required, so that it is preferably 0.5 or more. However, implementation is possible even if it is less than 0.5. On the other hand, when the molar ratio of water to the alkylaluminum compound exceeds 1.3, a gel or solid insoluble in the solvent may be deposited, and it may be difficult to form a uniform film due to the gel or solid. In addition, when gel or solid precipitates when the molar ratio of water exceeds 1.3, or even when the molar ratio of water is 1.3 or less, it should be removed by filtration. Is also possible. However, this is not preferable because it leads to loss of aluminum. The molar ratio to the alkylaluminum compound is preferably in the range of 0.6 to 1.3, more preferably in the range of 0.7 to 1.2, still more preferably in the range of 0.8 to 1.1, and still more preferably 0. A partial hydrolyzate is obtained using water in the range of 9 to 1.1.

  The non-aqueous solvent of the present invention refers to a solvent other than water. Specific examples of the non-aqueous solvent include N-methyl-2-pyrrolidone, 1,3-dimethyl-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H)- Cyclic amides such as pyrimidinone, aliphatic hydrocarbons such as n-hexane, octane, and n-decane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; benzene, toluene, xylene, cumene, etc. Aromatic hydrocarbons; Hydrocarbon solvents such as mineral spirit, solvent naphtha, kerosene, petroleum ether, etc .; diethyl ether, tetrahydrofuran, diisopropyl ether, dioxane, di-n-butyl ether, dialkylethylene glycol, dialkyldiethylene glycol, dialkyltriethyleneglycol Ethers such as Le, can be cited glyme, diglyme, triglyme solvent like. The non-aqueous solvent is preferably N-methyl-2-pyrrolidone, 1,3-dimethyl-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone, n -Hexane, octane, n-decane, cyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, benzene, toluene, xylene, cumene, mineral spirit, solvent naphtha, kerosene, petroleum ether, diethyl ether, tetrahydrofuran, diisopropyl ether, dioxane, dioxane -One or more solvents selected from the group consisting of n-butyl ether, dialkylethylene glycol, dialkyldiethylene glycol, dialkyltriethylene glycol, glyme, diglyme, and triglyme. These non-aqueous solvents can be variously selected depending on production conditions and use conditions. For example, an amide solvent such as N-methyl-2-pyrrolidone is preferably used at the time of producing an electrode, and is preferably toluene, Aromatic hydrocarbon solvents such as xylene are preferable because they are widely used industrially, and ether solvents such as tetrahydrofuran and glyme are preferable because they are coordinated with alkylaluminum partial hydrolysates and stabilized.

  The partial hydrolyzate of the alkylaluminum compound in the method of the present invention is presumed to be a mixture of compounds containing a structural unit represented by the following general formula (3).

(In the formula, R ³ is the same as R ¹ in the general formula (1) and R ² in the general formula (2), and m is an integer of 1 to 80.)

  Such a partial hydrolyzate of an alkylaluminum compound is industrially used together with a transition metal compound as a catalyst component for olefin, styrene and butadiene polymerization, and is composed of a combination of a linear type and a branched type or a cyclic type. It is a mixture.

  Also in the composition for producing a positive electrode active material, the partial hydrolyzate of the alkylaluminum compound is preferably a mixture of compounds containing the structural unit represented by the general formula (3). Furthermore, the composition for producing a positive electrode active material may be a composition further containing the above-mentioned one or two or more non-aqueous solvents.

The positive electrode active material in the present invention is preferably an active material for a lithium secondary battery positive electrode. In this case, the positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. For example, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFeO ₂ , LiNi _0.5 Mn _1.5 O ₂ , LiNi _x Co _y Al _z O ₂ (x + y + z = 1), LiNi _x Co _y Mn _z O ₂ ( Examples thereof include lithium transition metal composite oxides such as x + y + z = 1) and lithium-containing transition metal phosphate compounds such as LiFePO ₄ , LiMnPO ₄ , and LiCoPO ₄ . LiMn ₂ O ₄ Among them, LiNi _0.5 Mn _1.5 O _4, a lithium transition metal composite oxide or LiCoO ₂ having a spinel structure and the _{like, LiNiO 2, LiNi x Co y} Al z O 2 (x + y + z = 1), LiNi x Co _y Mn _z O ₂ by an aluminum oxide coating to the oxide of a transition metal having an (x + y + z = 1 ) layered structure such preferable because of high effect of improving the battery performance. Although the detailed mechanism is not clear, in the lithium transition metal composite oxide having a spinel structure formed with the aluminum oxide film produced by the method of the present invention, elution of Mn from the composite oxide is suppressed. Inferred. In addition, in the transition metal oxide having a layered structure formed with the aluminum oxide film produced by the method of the present invention, the crystal structure of the oxide can be strengthened.

  The addition amount of the alkylaluminum compound partial hydrolyzate with respect to the positive electrode active material is in the range of 0.01 to 10 parts by mass, preferably 0.05 to 4 parts by mass, in terms of alumina, with respect to 100 parts by mass of the positive electrode active material. Preferably it is 0.2-2 mass parts. When the amount is less than 0.01 parts by mass, the coating treatment efficiency is lowered, so that a sufficient addition effect cannot be obtained. When the amount exceeds 10 parts by mass, the film thickness of the film increases and the resistance value may increase. The addition amount of the partial hydrolyzate can be appropriately determined in consideration of the performance of the obtained positive electrode active material.

  The method of coating the positive electrode active material with a partial hydrolyzate of alkyl aluminum is not particularly limited. For example, a partial hydrolyzate solution of alkyl aluminum may be added to a suspension of the active material in a non-aqueous solvent, or the positive electrode active material is mixed with a conductive additive or a binder and processed into a sheet shape. Then, it can be coated by a method such as spraying or dipping.

  In the method of the present invention, the positive electrode active material is coated with a partial hydrolyzate of alkylaluminum and then baked to convert the partial hydrolyzate into an oxide. The firing conditions may be any conditions that do not deteriorate the performance of the composite oxide serving as the positive electrode active material and can form a suitable coating by converting the partial hydrolyzate into an oxide. As a calcination temperature, it can be set as 50 degreeC-1000 degreeC, for example, Preferably, it is 100-900 degreeC, More preferably, it is 150-800 degreeC, More preferably, it can be set as the range of 200-700 degreeC. Even if firing at a temperature exceeding 800 ° C., the effect is not different from the case of 800 ° C. or lower, or the crystal structure of the positive electrode active material changes, which may adversely affect battery performance. In addition, when the temperature is lower than 100 ° C., the coexistence of moisture due to moisture absorption or the like is insufficient, and the battery performance may be deteriorated due to other factors such as moisture content. The firing time can be appropriately determined in consideration of the degree of conversion of the partial hydrolyzate into an oxide, the change in the crystal structure of the positive electrode active material, and the like according to the firing temperature. For example, it is in the range of 10 minutes to 10 hours, preferably in the range of 30 minutes to 5 hours. However, it is not intended to be limited to these numerical ranges.

  By the firing, a composite material in which an aluminum oxide film is formed on at least a part of the surface of the composite oxide is obtained. This composite material is preferably used as a positive electrode active material, more preferably as a positive electrode active material for a lithium secondary battery. Is preferred. By using a positive electrode using this composite material as a positive electrode active material, advantages such as providing a lithium secondary battery with significantly improved charge / discharge cycle life can be obtained.

  The present invention also includes a non-aqueous electrolyte secondary battery including a positive electrode used as the positive electrode active material of the present invention. In addition to the positive electrode, the battery can include a negative electrode and a separator.

  The negative electrode material is not particularly limited as long as it is a material usually used for a lithium secondary battery. For example, metallic lithium or a lithium alloy such as tin, silicon, silica, or a carbon material that can be doped / undoped with lithium ions, etc. It can be illustrated.

  As the separator, a microporous film or the like is used, and as a material, a polyolefin resin such as polyethylene or polypropylene, or a fluorine resin such as polyvinylidene fluoride, or the like is used.

  The lithium secondary battery of this invention contains electrolyte solution in addition to the said positive electrode, a negative electrode, and a separator. As the electrolytic solution, a nonaqueous electrolytic solution is used, and a nonaqueous electrolytic solution commonly used for lithium secondary batteries can be used. Examples of the solvent for the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, and bis (2,2 , 2-trifluoroethyl) carbonate, chain carbonates such as γ-butyrolactone, γ-valerolactone, propiolactone, cyclic esters such as methyl acetate, methyl butyrate, ethyl trifluoroacetate, diisopropyl ether, Simple ethers such as tetrahydrofuran, dioxolane, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and nitriles such as acetonitrile and benzonitrile. Mention may be made of one or a mixture of two or more thereof.

As the electrolyte salt constituting the nonaqueous electrolytic solution, a lithium salt that is stable in a wide potential region can be used. Examples of such electrolyte salts include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). ₃ , Mg (ClO ₄ ) ₂ , Mg (CF ₃ SO ₃ ) ₂ , Mg (N (CF ₃ SO ₂ ) ₂ ) _{2 and the} like. These may be used alone or in combination of two or more. In addition, the density | concentration of the electrolyte salt in a non-aqueous electrolyte can be made into the range of 0.2-2.5 mol / L, for example. The concentration of the electrolyte salt in the non-aqueous electrolyte can be appropriately determined in consideration of the type of the electrolyte salt and the like from the viewpoint of obtaining good high rate charge / discharge characteristics of the battery.

  Although the shape and form of the nonaqueous electrolyte secondary battery are not particularly limited, a cylindrical type, a square type, a coin type, a card type, a laminate type, and the like are usually selected.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.

(Preparation Example 1)
9 g of triethylaluminum (manufactured by Tosoh Finechem, hereinafter abbreviated as TEAL) was added to 20 g of N-methyl-2-pyrrolidone (battery grade manufactured by Kishida Chemical, hereinafter abbreviated as NMP) and sufficiently stirred. Thereafter, 7 g of NMP solution containing 20% by mass of water at 25 ° C. ([H 2 O] / [TEAL] = 1.0, mol / mol) was added dropwise over 50 minutes. The maturation reaction was carried out by continuing stirring for 5 hours under a temperature condition of 25 ° C. to obtain an NMP solution of TEAL partial hydrolyzate (ethylaluminoxane) (hereinafter referred to as EAO / NMP).
When the solvent was removed from the obtained EAO / NMP solution and IR measurement was performed by the permeation method, a broad Al—O—Al vibration peak was confirmed in the vicinity of 400 to 1500 cm ⁻¹ , and Al—O—Al by hydrolysis was confirmed. Bond formation was confirmed. The IR results measured by the transmission method are shown in FIG.

[Example 1]
Lithium cobaltate (manufactured by Aldrich, 99.8% trace metals basis, hereinafter abbreviated as LiCoO ₂ ) was used which was dried at 100 ° C. and 5 kPa for about 3 hours. Under a nitrogen stream, 7 g of NMP was added to 15 g of LiCoO ₂ pretreated, and stirred in a slurry state. To this slurry solution was added 1.8 g of the EAO / NMP solution (Al concentration: 6.2% by mass) prepared in Preparation Example 1 (LiCoO ₂ in terms of alumina, ₂ parts by mass with respect to 100 parts by mass) and stirred overnight. . Next, after distilling off the solvent using an evaporator, it was transferred to a crucible in the atmosphere and subjected to a baking treatment at 700 ° C. for 1 hour. As a result of measuring the Al concentration in the obtained Al oxide-coated LiCoO ₂ using an ICP issuance spectroscopic analyzer, it was confirmed that the Al concentration was 0.6 mass%, which was almost the theoretical value.
Acetylene black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder were blended with the obtained oxidized Al-coated LiCoO _{2 so} as to be oxidized Al-coated LiCoO ₂ : acetylene black: PVDF = 94: 3: 3, and NMP was added. The slurry used was applied to an aluminum current collector with a certain film thickness and dried to obtain a positive electrode sheet.

As an electrolyte solvent, a solvent (battery grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (hereinafter abbreviated as EC) and ethyl methyl carbonate (hereinafter abbreviated as EMC) are mixed at a volume ratio of 3: 7 is used. those of lithium hexafluorophosphate (LiPF ₆₎ was dissolved 1.0 mol / L was used as the electrolyte.
A lithium secondary battery using a coin-type cell having the structure shown in FIG. 1 is prepared by using a metal lithium foil (0.5 mm thickness, manufactured by Honjo Chemical Co., Ltd.) as the negative electrode active material and a polyolefin porous film containing an inorganic filler as the separator. did. In the lithium secondary battery, a positive electrode 1 and a negative electrode 4 are arranged opposite to each other with a separator 6 interposed therebetween, a stainless steel leaf spring 5 is installed on a negative electrode stainless steel cap 3, and a laminate including the negative electrode 4, the separator 6, and the positive electrode 1 is coin-shaped. Stored in the cell. After injecting the electrolytic solution of the present invention into this laminate, the gasket 7 was placed, then the cap 2 made of a positive electrode stainless steel was covered, and the coin-type cell case was crimped.

A coin cell type lithium secondary battery (half cell) made of Al oxide-coated LiCoO ₂ positive electrode and metallic lithium prepared by the above method is charged at a constant current of 25 ° C. with a charging current of 0.1 CmA and an upper limit voltage of 4.2 V. Subsequently, the battery was discharged at a discharge current of 0.1 CmA until it reached 3.0V. After performing this operation three times, constant current-low voltage charging was performed up to 4.5 V with a charging current of 1 CmA under a constant temperature condition of 50 ° C., and constant current discharging was performed up to a final voltage of 3.0 V with a discharging current of 1 CmA. . The discharge capacity at this time was taken as the initial discharge capacity, the discharge capacity when this operation was repeated 50 times was measured, and the comparison was made with the discharge capacity / initial discharge capacity ratio after 50 cycles as the cycle retention rate. The results are shown in Table 1.

(Preparation Example 2)
An EAO / THF solution was prepared in the same manner as in Preparation Example 1, except that the solvent was changed to tetrahydrofuran (hereinafter abbreviated as THF).

[Example 2]
A positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1 except that the EAO / THF solution obtained in Preparation Example 2 was used, and a charge / discharge test was performed. The results are shown in Table 1.

(Preparation Example 3)
24 g of TEAL was added to 57 g of toluene and sufficiently stirred. Thereafter, 19 g of a THF solution containing 20% by mass of water at 25 ° C. ([H ₂ O] / [TEAL] = 1.0, mol / mol) was dropped over about 2 hours. The aging reaction was carried out by continuing stirring for 5 hours under a temperature condition of 25 ° C. to obtain an EAO / toluene solution. When IR was measured by the transmission method in the same manner as in Preparation Example 1, a broad vibration peak of Al—O—Al was confirmed in the vicinity of 400 to 1500 cm ⁻¹ , and formation of an Al—O—Al bond by hydrolysis was confirmed. .

[Example 3]
A positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1 except that the EAO / toluene solution obtained in Preparation Example 3 was used, and a charge / discharge test was performed. The results are shown in Table 1.

(Preparation Example 4)
An EAO / xylene solution was prepared in the same manner as in Preparation Example 3 except that the solvent was changed to xylene.

[Example 4]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 1 except that the EAO / xylene solution obtained in Preparation Example 4 was used, and a charge / discharge test was performed. The results are shown in Table 1.

[Comparative Example 1]
Without performing the coating treatment of LiCoO ₂ used in Example 1, a positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1, and a charge / discharge test was performed. The results are shown in Table 1.

[Comparative Example 2]
An aqueous aluminum sulfate solution was added to 15 g of LiCoO ₂ used in Example 1 so as to be 2 parts by mass in terms of alumina. After stirring overnight, the active material was filtered off and baked in the atmosphere at 700 ° C. for 1 hour. Using the thus obtained aluminum sulfate-treated positive electrode, a positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1, and a charge / discharge test was performed. The results are shown in Table 1.

As is apparent from Table 1, it can be seen that the LiCoO ₂ positive electrode coated with Al oxide has an improved cycle capacity retention rate as compared with LiCoO ₂ not subjected to the coating treatment. As is confirmed in Comparative Example 2, it is considered that the addition of the aluminum compound has an effect.
On the other hand, although the cause of the difference in the cycle capacity retention rate between Examples 1 to 4 and Comparative Example 2 is not clear, for example, impurities (sulfate ions), or Al oxide coating prepared by the production method of the present invention This is probably due to the formation of different Al oxide coatings.

[Example 5]
The amount of EAO / NMP solution of Example 1 was 1/2, prepare the oxide Al coated LiCoO ₂ except adding 1 part by weight in terms of alumina with respect to LiCoO _2, 100 parts by weight in the same manner as in Example 1 did. Using this Al oxide-coated LiCoO ₂ , a positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1, and a charge / discharge test was performed. The results are shown in Table 2.

[Example 6]
A positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 5 except that the Al oxide coating amount was changed to 0.5 parts by mass in terms of alumina, and a charge / discharge test was performed. The results are shown in Table 2.

[Example 7]
A positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 5 except that the amount of Al oxide coating was 0.05 parts by mass in terms of alumina, and a charge / discharge test was performed. The results are shown in Table 2.

[Example 8]
After coating with the EAO / NMP solution, a positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1 except that the firing temperature was 180 ° C., and a charge / discharge test was performed. The results are shown in Table 2.

[Example 9]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 8 except that the Al oxide coating amount was 1.0 parts by mass in terms of alumina, and a charge / discharge test was performed. The results are shown in Table 2.

[Example 10]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 8 except that the Al oxide coating amount was changed to 0.5 parts by mass in terms of alumina, and a charge / discharge test was performed. The results are shown in Table 2.

[Example 11]
After coating with the EAO / NMP solution, a positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 5 except that the firing temperature was 100 ° C., and a charge / discharge test was performed. The results are shown in Table 2.

In Examples 5 to 7, the influence of the Al oxide coating amount was examined. As a result, it was confirmed that the cycle capacity retention ratio was improved even when 0.05 parts by mass of EAO / NMP in terms of alumina was used with respect to 100 parts by mass of LiCoO ₂ . This suggests that a very small amount of alkylaluminum partial hydrolyzate coating is effective.
Further, Examples 5, 7 and 11 are examples examined by changing the firing temperature with the same amount of alumina coating. Surprisingly, even in the case of the cathode active material fired at 100 ° C., the uncoated cathode active material It was found that the cycle capacity retention rate was improved compared to This effect, like aluminum hydroxide, is a surprising effect that cannot be achieved with an alumina precursor.

(Preparation Example 5)
34 g of triisobutylaluminum (manufactured by Tosoh Finechem Co., Ltd., hereinafter abbreviated as TIBAL) was added to 136 g of hexane (industrial grade Zeolum dehydrated, hereinafter abbreviated as HX), and sufficiently stirred. Thereafter, 2 g of water ([H ₂ O] / [TIBAL] = 0.7, mol / mol) was added dropwise at 50 ° C. over 50 minutes. Aging was performed for 1 hour under a temperature condition of 0 ° C., and further the temperature was raised to 25 ° C., followed by stirring for 5 hours to complete the aging reaction, and a hexane solution of TIBAL partial hydrolyzate (butylaluminoxane) (hereinafter referred to as BAO). / HX).
When the solvent was removed from the obtained BAO / HX solution and IR measurement was performed by a permeation method, a broad Al—O—Al vibration peak was observed in the vicinity of 400 to 1500 cm ⁻¹ , and Al—O—Al by hydrolysis was confirmed. Bond formation was confirmed. The IR results measured by the transmission method are shown in FIG.

[Example 12]
A positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 1 except that the BAO / HX solution obtained in Preparation Example 5 was used, and a charge / discharge test was performed. The results are shown in Table 3.

(Preparation Example 6)
24 g of diisobutylaluminum hydride (manufactured by Tosoh Finechem, hereinafter abbreviated as DIBAL-H) was added to 125 g of hexane and sufficiently stirred. Then, 2 g ([H ₂ O] / [DIBAL-H] = 0.7, mol / mol) of water was added dropwise at 0 ° C. over 1 hour. The mixture was aged for 1 hour under a temperature condition of 0 ° C., and further heated to 25 ° C., and then stirred for 5 hours to complete the aging reaction. A DIBAL-H partial hydrolyzate (dibutylaluminoxane) in hexane , DBAO / HX) was obtained.
When the solvent was removed from the obtained DBAO / HX solution and IR measurement was performed by a transmission method, a broad vibration peak of Al—O—Al was confirmed in the vicinity of 400 to 1500 cm ⁻¹ , and Al—O—Al by hydrolysis was confirmed. Bond formation was confirmed.

[Example 13]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 1 except that the DBAO / HX solution obtained in Preparation Example 6 was used, and a charge / discharge test was performed. The results are shown in Table 3.

  Examples 12 and 13 describe the results of studies on triisobutylaluminum and diisobutylaluminum hydride. It was confirmed that the alumina coating can be formed even when the functional group bonded to aluminum is different, and the battery performance is improved.

[Example 14]
4.6 g of NMP was mixed with 10 g of LiCoO ₂ (manufactured by Aldrich), and 0.42 g of an EAO / NMP solution (Al concentration 6.4% by mass) synthesized in the same manner as in Preparation Example 1 was mixed under a nitrogen atmosphere. A reflux apparatus was attached to the mixed solution, and the mixture was heated to 204 ° C. under a nitrogen stream and stirred continuously for 27 hours. After cooling this solution, acetylene black (AB) and PVdF were blended at a weight ratio of LiCoO2: AB: PVdF = 94: 3: 3, and slurried using NMP to an aluminum current collector with a certain film thickness And dried to obtain a positive electrode sheet.

Using the obtained positive electrode sheet, a coin cell type lithium secondary battery was prepared in the same manner as in Example 1. A coin cell type lithium secondary battery (half cell) made of the prepared Al oxide-coated LiCoO ₂ positive electrode and metallic lithium was charged at a constant current of 25 ° C. with a charging current of 0.1 CmA and an upper limit voltage of 4.2 V, followed by It discharged until it became 3.0V with the discharge current of 0.1 CmA. After this operation was performed three times, constant current-low voltage charging was performed up to 4.5 V with a charging current of 1 CmA under a constant temperature of 25 ° C., and constant current discharging was performed up to a final voltage of 3.0 V with a discharging current of 1 CmA. . The discharge capacity at this time was defined as the initial discharge capacity, the discharge capacity when this operation was repeated 100 times was measured, and the comparison was performed using the discharge capacity / initial discharge capacity ratio after 100 cycles as the cycle retention rate. The results are shown in Table 4.

[Example 15]
A positive electrode sheet and a coin cell type lithium secondary battery were produced in the same manner as in Example 14 except that the heating time was 6 hours, and a charge / discharge cycle test was conducted. The results are shown in Table 4.

[Example 16]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 14 except that the heating temperature was 150 ° C., and a charge / discharge cycle test was performed. The results are shown in Table 4.

[Example 17]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 14 except that the heating temperature was 50 ° C., and a charge / discharge cycle test was performed. The results are shown in Table 4.

[Comparative Example 3]
Without performing the LiCoO ₂ coating treatment as in Example 14, a positive electrode sheet and a coin cell type lithium secondary battery were manufactured using LiCoO ₂ (manufactured by Aldrich). Table 4 shows the results of the charge / discharge test conducted in the same manner as in Example 14.

[Example 18]
4.6 g of NMP was added to 10 g of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by MTI Corporation) and stirred in a slurry state. 0.42 g of the EAO / NMP solution (Al concentration 6.4% by mass) used in Example 14 in this slurry solution (based on 100 parts by mass of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ in terms of alumina) 0.5 parts by mass) and stirred at room temperature for 3 hours. Next, after distilling off the solvent using an evaporator, it was transferred to a crucible in the air and subjected to a baking treatment for 2 hours under a temperature condition of 200 ° C. As a result of measuring the Al concentration in the obtained Al oxide-coated LiNi _1/3 Co _1/3 Mn _1/3 O ₂ using an ICP emission spectroscopic analyzer, the Al concentration was 0.15% by mass, which was almost the theoretical value. It was confirmed that the Al concentration was as expected.

The obtained oxidized Al-coated LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is made of AB as a conductive additive and PVdF as a binder so that the oxidized Al-coated LiCoO ₂ : AB: PVDF = 94: 3: 3. What was blended and slurried with NMP was applied on an aluminum current collector with a certain film thickness and dried to obtain a positive electrode sheet.

Using this positive electrode sheet, a coin cell type lithium secondary battery was produced in the same manner as in Example 1. Coin cell type lithium secondary battery (half cell) made with the prepared Al oxide-coated LiNi _1/3 Co _1/3 Mn _1/3 O ₂ positive electrode and metallic lithium at a constant current of 25 ° C. with a charging current of 0.1 CmA The battery was charged with an upper limit voltage of 4.3 V, and then discharged to 3.0 V with a discharge current of 0.1 CmA. After this operation was performed three times, constant current-low voltage charging was performed up to 4.6 V with a charging current of 1 CmA under a constant temperature condition of 25 ° C., and constant current discharging was performed up to a final voltage of 3.0 V with a discharging current of 1 CmA. . The discharge capacity at this time was defined as the initial discharge capacity, the discharge capacity when this operation was repeated 100 times was measured, and the comparison was performed using the discharge capacity / initial discharge capacity ratio after 100 cycles as the cycle retention rate. The results are shown in Table 5.

[Example 19]
Except that the heating temperature was set to 500 ° C., an Al oxide-coated LiNi _1/3 Co _1/3 Mn _1/3 O ₂ positive electrode sheet and a coin cell type lithium secondary battery were prepared in the same manner as in Example 18, and charge / discharge was performed. A cycle test was conducted. The results are shown in Table 5.

[Example 20]
The heating temperature to _{700 ℃, LiNi 1/3 Co 1/3 Mn} 1/3 oxidized with O ₂ per part by weight of the EAO / NMP solution in the same manner as in Example 18 except for adding Al coated LiNi _{1 A / 3} Co _1/3 Mn _1/3 O ₂ positive electrode sheet and a coin cell type lithium secondary battery were prepared and subjected to a charge / discharge cycle test. The results are shown in Table 5.

[Comparative Example 4]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by MTI Corporation) before the coating treatment. Table 5 shows the results of a charge / discharge test performed in the same manner as in Example 18.

[Example 21]
4.6 g of NMP was added to 10 g of lithium manganate (LiMn ₂ O ₄ , purchased from Hosen Co., Ltd.), and stirred in a slurry state. To this slurry solution was added 0.42 g of the EAO / NMP solution (Al concentration 6.4% by mass) used in Example 14 (LiMn ₂ O _{4 in} terms of alumina, 0.5 parts by mass with respect to 100 parts by mass). Stir for hours at room temperature. Next, after distilling off the solvent using an evaporator, it was transferred to a crucible in the atmosphere, and calcination was performed for 2 hours at a temperature of 700 ° C. As a result of measuring the Al concentration in the obtained Al oxide-coated LiMn ₂ O ₄ using an ICP issuance spectroscopic analyzer, it was confirmed that the Al concentration was 0.15% by mass, which was almost the theoretical value of Al. It was.

Resulting oxidized Al-coated LiMn ₂ O ₄ acetylene black as a conductive aid, oxidizing polyvinylidene fluoride (PVDF) as a binder Al coated LiMn ₂ O _4: acetylene black: PVdF = 88: 6: 6 and so as formulated Then, a slurry made using NMP was applied on an aluminum current collector with a certain film thickness and dried to obtain a positive electrode sheet.

Using this positive electrode sheet, a coin cell type lithium secondary battery was produced in the same manner as in Example 1. A coin cell type lithium secondary battery (half cell) made of the prepared Al oxide-coated LiMn ₂ O ₄ positive electrode and metallic lithium was charged at a constant current of 25 ° C. with a charging current of 0.1 CmA and an upper limit voltage of 4.2 V, Then, it discharged until it became 3.0V with the discharge current of 0.1 CmA. After this operation was performed three times, constant current-low voltage charging was performed up to 4.5 V with a charging current of 1 CmA under a constant temperature of 25 ° C., and constant current discharging was performed up to a final voltage of 3.0 V with a discharging current of 1 CmA. . The discharge capacity at this time was defined as the initial discharge capacity, the discharge capacity when this operation was repeated 100 times was measured, and the comparison was performed using the discharge capacity / initial discharge capacity ratio after 100 cycles as the cycle retention rate. The results are shown in Table 6.

[Comparative Example 5]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared using LiMn ₂ O ₄ (purchased from Hosen Co., Ltd.) before the coating treatment. Table 6 shows the results of a charge / discharge test performed in the same manner as in Example 21.

(Preparation Example 7)
To 2120 g of toluene (industrial product, dehydrated product), 420 g of trimethylaluminum (industrial product, hereinafter abbreviated as TMAL) was added and sufficiently stirred. Under nitrogen flow, the internal temperature was adjusted to 0 ° C., and 76 g of ion-exchanged water ([H ₂ O] / [TMAL] = 0.73, mol / mol) was added dropwise over 20 hours. After completion of the dropping, the mixture was heated to 50 ° C. and stirred for 1 hour to conduct an aging reaction to obtain a toluene solution of TMAL partial hydrolyzate (methylaluminoxane) (hereinafter MAO / Tol).

  As a result of measuring 1H-NMR spectrum of the obtained MAO / Tol solution, a characteristic spectrum of methylaluminoxane was confirmed at -0.5 to -1.2 ppm, and Al-O-Al (CH3) n by hydrolysis was confirmed. The formation of was confirmed.

When the solvent was removed from the obtained MAO / Tol solution and IR measurement was performed by the transmission method, a broad vibration peak of Al—O—Al was confirmed in the vicinity of 400 to 1000 cm ⁻¹ , and Al—O—Al by hydrolysis was confirmed. Bond formation was confirmed. FIG. 4 shows the IR results measured by the transmission method.
[Example 22]
6.2 g of NMP was added to 10 g of LiCoO ₂ (manufactured by Aldrich) and stirred in a slurry state. To this slurry solution, 1.0 g of MAO / Tol solution prepared in Preparation Example 7 (Al concentration 4.7 mass%) (LiCoO ₂ in terms of alumina, 1 mass part per 100 mass parts) was added and stirred overnight. . Next, after distilling off the solvent using an evaporator, it was transferred to a crucible in the atmosphere and baked for 2 hours under a temperature condition of 150 ° C. As a result of measuring the Al concentration in the obtained Al oxide-coated LiCoO ₂ using an ICP issuance spectroscopic analyzer, it was confirmed that the Al concentration was 0.3% by mass, which was almost the theoretical value.

A mixture of AB obtained as a conductive auxiliary agent and PVDF as a binder in the obtained Al oxide-coated LiCoO _{2 so} as to be an oxide Al-coated LiCoO ₂ : AB: PVDF = 94: 3: 3 and slurried using NMP. A positive electrode sheet was obtained by coating the aluminum current collector with a constant film thickness and drying.

Using this positive electrode sheet, a coin cell type lithium secondary battery was produced in the same manner as in Example 1. A coin cell type lithium secondary battery (half cell) made of the prepared Al oxide-coated LiCoO ₂ positive electrode and metallic lithium was charged at a constant current of 25 ° C. with a charging current of 0.1 CmA and an upper limit voltage of 4.3 V, followed by It discharged until it became 3.0V with the discharge current of 0.1 CmA. After this operation was performed three times, constant current-low voltage charging was performed up to 4.6 V with a charging current of 1 CmA under a constant temperature condition of 25 ° C., and constant current discharging was performed up to a final voltage of 3.0 V with a discharging current of 1 CmA. . The discharge capacity at this time was defined as the initial discharge capacity, the discharge capacity when this operation was repeated 100 times was measured, and the comparison was performed using the discharge capacity / initial discharge capacity ratio after 100 cycles as the cycle retention rate. The results are shown in Table 7.

[Example 23]
A positive electrode sheet was prepared by synthesizing AlCo-coated LiCoO ₂ by the same method as in Example 22 except that the heating temperature was 200 ° C. Using the obtained positive electrode sheet, a coin cell type lithium secondary battery was produced in the same manner as in Example 21, and a charge / discharge cycle test was conducted. The results are shown in Table 7.

Table 7 also shows the results of the LiCoO ₂ positive electrode not subjected to the coating treatment used in Comparative Example 3 for comparison.

[Example 24]
4.9 g of NMP was added to 10 g of lithium nickel manganate (LiNi _0.5 Mn _1.5 O ₄ , manufactured by Toshima Seisakusho Co., Ltd.) and stirred in a slurry state. To this slurry solution, 0.44 g (LiNi _0.5 Mn _1.5 O _{4 in} terms of alumina, _0.5 parts by mass with respect to 100 parts by mass) of the EAO / NMP solution (Al concentration 6.4% by mass) used in Example 14 was added. For 9 hours at room temperature. Next, after distilling off the solvent using an evaporator, it was transferred to a crucible in the air and subjected to a baking treatment for 2 hours under a temperature condition of 200 ° C. As a result of measuring the Al concentration in the obtained Al oxide-coated LiNi _0.5 Mn _1.5 O ₄ using an ICP issuance spectroscopic analyzer, the Al concentration is 0.26% by mass, which is almost the theoretical value of Al. confirmed.

The obtained oxidized Al-coated LiNi _0.5 Mn _1.5 O ₄ was coated with acetylene black as a conductive assistant and polyvinylidene fluoride (PVdF) as a binder. The oxidized Al-coated LiNi _0.5 Mn _1.5 O ₄ : acetylene black: PVDF = 88: 6: 6 What was blended as described above and slurried using NMP was applied on an aluminum current collector with a certain film thickness and dried to obtain a positive electrode sheet.

Using this positive electrode sheet, a coin cell type lithium secondary battery was produced in the same manner as in Example 1. A coin cell type lithium secondary battery (half cell) made with the prepared Al oxide-coated LiNi _0.5 Mn _1.5 O ₄ positive electrode and metallic lithium is charged at a constant current of 25 ° C. with a charging current of 0.1 CmA and an upper limit voltage of 4.8 V. Subsequently, the battery was discharged at a discharge current of 0.1 CmA until it reached 3.0V. After performing this operation three times, under a constant temperature of 25 ° C., constant current-low voltage charging was performed up to 5.0 V with a charging current of 1 CmA, and constant current discharging was performed up to a final voltage of 3.0 V with a discharging current of 1 CmA. . The discharge capacity at this time was defined as the initial discharge capacity, the discharge capacity when this operation was repeated 100 times was measured, and the comparison was performed using the discharge capacity / initial discharge capacity ratio after 100 cycles as the cycle retention rate. The results are shown in Table 8.

[Comparative Example 6]
A positive electrode sheet and a coin cell type lithium secondary battery were prepared using LiNi _0.5 Mn _1.5 O ₄ (manufactured by Toshima Seisakusho Co., Ltd.) before the coating treatment. Table 8 shows the results of a charge / discharge test performed in the same manner as in Example 24.

  It is possible to provide a method for producing a positive electrode active material for a lithium secondary battery, which is industrially simple, has little damage to the active material, and has an aluminum film with reduced impurities. Furthermore, the lithium secondary battery using the positive electrode active material produced by the method of the present invention has a significantly improved charge / discharge cycle life.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode stainless steel cap 3 Negative electrode stainless steel cap 4 Negative electrode 5 Stainless steel leaf spring 6 Polyolefin porous separator 7 containing an inorganic filler 7 Gasket

Claims (15)

  Partial hydrolysis of an alkylaluminum compound which is a dialkylaluminum, a trialkylaluminum or a mixture thereof (provided that the alkyl groups in the dialkylaluminum and the trialkylaluminum can be the same or different and have 1 to 8 carbon atoms) A step of forming a coating of the partial hydrolyzate on at least a part of the surface of the composite oxide of lithium and transition metal using the product, and firing the composite oxide formed with the coating of the partial hydrolyzate A method for producing a positive electrode active material comprising a composite oxide having an aluminum oxide coating, comprising a step of forming a composite oxide having an aluminum oxide coating.   2. The production method according to claim 1, wherein the partial hydrolyzate is used for coating the composite oxide as a mixture with a non-aqueous solvent. The production method according to claim 1 or 2, wherein the dialkylaluminum is an alkylaluminum compound represented by the following general formula (1).
(In the formula, R ¹ is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group, and X represents a halogen atom such as hydrogen, fluorine, chlorine, bromine or iodine. The manufacturing method in any one of Claims 1-3 whose said trialkylaluminum is an alkylaluminum compound represented by following General formula (2).
(In the formula, R ² is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group.   The manufacturing method according to claim 1, wherein the lithium-transition metal composite oxide includes a lithium transition metal composite oxide or a lithium-containing transition metal phosphate compound. The composite oxide of lithium and transition metal is LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFeO ₂ , LiNi _0.5 Mn _1.5 O ₂ , LiNi _x Co _y Al _z O ₂ (x + y + z = 1), LiNi _{x Co y Mn z O 2 (} x + y + z = 1), LiFePO 4, LiMnPO 4, and LiCoPO comprising one or more composite oxides selected from the group consisting of _4, method according to claims 1-4.   The manufacturing method according to any one of claims 1 to 6, wherein a coating amount of the partial hydrolyzate with respect to the composite oxide is 0.01 to 10 parts by mass in terms of alumina with respect to 100 parts by mass of the composite oxide. .   The said baking is a manufacturing method in any one of Claims 1-7 implemented at the temperature of the range of 50 to 1000 degreeC.   The manufacturing method in any one of Claims 1-8 whose mass ratio of the complex oxide and aluminum oxide film in the said positive electrode active material is the range of 100: 0.01-10.   The manufacturing method of Claims 1-9 whose positive electrode active material is for lithium secondary batteries.   The manufacturing method of a positive electrode including manufacturing a positive electrode active material by the method in any one of Claims 1-10, and obtaining a positive electrode using the obtained positive electrode active material.   The manufacturing method of a lithium secondary battery which manufactures a positive electrode by the method of Claim 11, and manufactures a lithium secondary battery using the positive electrode and negative electrode which were obtained, a separator, and a non-aqueous electrolyte.   Partial hydrolysis of an alkylaluminum compound which is a dialkylaluminum, a trialkylaluminum or a mixture thereof (provided that the alkyl groups in the dialkylaluminum and the trialkylaluminum can be the same or different and have 1 to 8 carbon atoms) A composition for producing a positive electrode active material comprising a composite oxide having an aluminum oxide film. The composition according to claim 13, wherein the partial hydrolyzate of the alkylaluminum compound is a mixture of compounds containing a structural unit represented by the following general formula (3).
(In the formula, R ³ is methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n -Represents an octyl group, m is an integer of 1-80.   The composition according to claim 13 or 14, further comprising one or more non-aqueous solvents.