JP2004281163A - Baked container for positive active material powder, positive active material powder, and lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the content of impurities and prevent adhesion of baking powder to a baked container when the positive active material powder comprising a lithium-containing composite oxide is prepared by baking specified raw material powder. <P>SOLUTION: The baked container provided with a dense ceramic coating layer having a silicon content of less than 5% on the inner surface of the container substrate is used to bake, the raw powder of the positive active material powder comprising the lithium-containing composite oxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a firing container for firing a predetermined raw material powder to obtain a positive electrode active material powder of a lithium ion secondary battery, a positive electrode active material powder obtained by firing, and a lithium ion comprising the same positive electrode active material powder The present invention relates to a secondary battery.
[0002]
[Prior art]
In recent years, as various electronic devices have become more portable and cordless, demand for non-aqueous electrolyte secondary batteries that are small, lightweight, and have high energy density has increased, and have superior characteristics compared to before. Development for non-aqueous electrolyte secondary batteries is desired.
[0003]
For the positive electrode material of the non-aqueous electrolyte secondary battery, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ Etc. are preferably used, especially LiCoO. ₂ Is widely used in terms of safety and capacity. As this material is charged, the lithium in the crystal lattice becomes lithium ions and desorbs into the electrolyte, while the lithium ions are reversibly inserted from the electrolyte into the crystal lattice along with the discharge. The function as an active material is expressed.
[0004]
As a method for producing lithium cobaltate, mixing and firing lithium carbonate and various cobalt sources is industrially carried out. In this industrial production, cobalt trioxide or cobalt oxyhydroxide is mainly used as a cobalt source.
[0005]
By the way, when the present inventors conducted a small-scale synthesis experiment using cobalt hydroxide, which is a precursor of cobalt tetroxide or cobalt oxyhydroxide as a cobalt source, there is an effect that the cost of the positive electrode material can be reduced. In addition, it was found that the use of specific cobalt hydroxide can improve battery capacity, safety, and cycle characteristics.
[0006]
However, as a next step, a test was conducted in which cobalt hydroxide and lithium carbonate were mixed and filled in a firing container and fired on a mass production scale. As a result, the amount of by-product cobalt oxide in the resulting lithium cobaltate was significantly increased. As a result, it has been found that there is a problem in that characteristics such as battery capacity decrease. In addition, when tribasic cobalt oxide or cobalt oxyhydroxide was used as a raw material, such difficulty in mass production was not observed.
[0007]
In addition, as a method for producing fluorine-containing lithium cobaltate, lithium carbonate, various cobalt sources, and fluorine-containing compounds are mixed and fired. As the cobalt source, tribasic cobalt oxide, cobalt oxyhydroxide, or cobalt hydroxide is used.
[0008]
However, as a result of a test in which a cobalt compound, lithium carbonate, and a fluorine-containing compound were mixed and filled in a large mullite firing container and fired, the fired powder was welded to the container wall surface of the container, It has been found that there is a problem that the fired powder cannot be discharged.
[0009]
Similarly, when the nickel-cobalt coprecipitated hydroxide, nickel-cobalt-manganese coprecipitated hydroxide and their coprecipitated oxyhydroxide or coprecipitated oxide powder, lithium compound and fluorine-containing compound powder are mixed and fired, When a mullite firing container is used as the firing container, there is a problem that the active material powder is welded to the vessel wall surface and is not discharged from the container, or a part of the container is separated and mixed into the active material powder.
[0010]
In addition, it replaces with the said mullite baking container, and MgAl proposed in patent documents 1 ₂ O ₄ The above various active material powders were fired using a spinel container of the above, but may be damaged easily due to thermal shock and mechanical shock during firing, the amount of by-product cobalt oxide increases, There are problems such as welding to the vessel wall. And MgAl ₂ O ₄ Spinel containers are expensive.
[0011]
[Patent Document 1]
JP 2002-216758 A
[0012]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to reduce the content of impurities when firing lithium-containing composite oxides or fluorine-containing lithium composite oxide powders, and to prevent the positive electrode active materials from being deposited on the vessel wall surface without the fluorine-containing compounds being deposited. The object is to provide a firing container capable of firing the material powder and to obtain a positive electrode active material powder suitable for a lithium ion secondary battery by firing in the firing container.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a positive electrode active material powder firing container for use in firing a predetermined raw material powder to obtain a positive electrode active material powder comprising a lithium-containing composite oxide. And a dense ceramic coating layer having a silicon content of less than 5%.
[0014]
If the silicon content is 5% or more, silicon and fluorine compounds or lithium compounds are likely to react with each other, and there is a possibility that the fired powder will be welded to the vessel wall surface. Most preferably it is free of silicon. If the ceramic coating layer is not dense, the lithium source and fluorine compound are absorbed into the coating layer, permeated through the coating layer and absorbed into the container substrate, or consumed and welded by chemical reaction with the container substrate. Since it becomes easy, it is not preferable.
[0015]
In order to suppress welding due to the reaction of the fluorine-containing compound with the container substrate, the ceramic coating layer is preferably made of at least one of spinel, macnesia, zirconia, and alumina having low chemical reactivity with the fluorine-containing compound. As the alumina, α-alumina having a poor chemical reactivity with lithium or fluorine is optimal.
[0016]
The porosity of the ceramic coating layer is preferably 15% or less. When the porosity exceeds 15%, the fluorine-containing compound is consumed by welding to the vessel wall surface or causing a chemical reaction with the vessel wall surface. A more preferable porosity is 10% or less.
[0017]
The thickness of the ceramic coating layer is preferably 50 to 500 μm. When the thickness is less than 50 μm, the durability of the coating layer becomes poor, and the fluorine-containing compound permeates the coating layer and is easily absorbed by the container substrate, which is not preferable. On the other hand, when the thickness exceeds 500 μm, interfacial peeling is likely to occur between the coating layer and the container substrate, which is not preferable.
[0018]
When spinel is used as the ceramic coating layer, Al is one of the spinels. ₂ MgO ₄ Can form a dense coating layer and has low chemical reactivity with the fluorine-containing compound, so that the fluorine-containing compound in the raw material powder does not weld to the firing container, which is particularly preferable. Al ₂ MgO ₄ As a lower layer of the layer, for example, by providing a mullite layer or an alumina layer by plasma spraying, Al ₂ MgO ₄ The adhesion between the layer and the container substrate can be further increased.
[0019]
The container substrate of the firing container according to the present invention is preferably porous mullite or cordierite from the viewpoint of heat resistance, thermal shock resistance and mechanical shock resistance. On the other hand, pure alumina is not preferred because it has poor thermal shock resistance and mechanical shock resistance and is expensive.
[0020]
In the present invention, various positive electrode active material powders suitable for lithium ion secondary batteries obtained by firing predetermined raw material powders using the above firing container provided with a dense ceramic coating layer having a silicon content of less than 5% (Lithium-containing composite oxide).
[0021]
It is known that when lithium is contained in the lithium-containing composite oxide, the safety of the lithium ion secondary battery is improved. However, by performing the firing in the firing container, the fluorine-containing compound is added to the vessel wall surface. A positive electrode active material powder made of fluorine-containing lithium cobalt oxide can be obtained without welding.
[0022]
Therefore, in the present invention, a cobalt compound powder, a lithium carbonate powder, and a fluorine-containing compound powder are mixed and filled in the fired container provided with a dense ceramic coating layer having a silicon content of less than 5%. The positive electrode active material powder which consists of a fluorine-containing lithium cobaltate baked in 1050 degreeC oxygen containing atmosphere is contained.
[0023]
Further, in the present invention, a cobalt hydroxide powder and a lithium carbonate powder are mixed and filled in the firing container provided with a dense ceramic coating layer having a silicon content of less than 5%, at 600 to 1050 ° C. A positive electrode active material powder made of lithium cobaltate that is fired in an oxygen-containing atmosphere is included.
[0024]
Since the firing container has a dense ceramic coating layer, the lithium source is hardly absorbed and absorbed by the coating layer or permeated through the coating layer to cause a chemical reaction with the container substrate. Therefore, an increase in the amount of by-product cobalt trioxide in the produced lithium cobaltate can be suppressed.
[0025]
Further, in the present invention, a nickel-cobalt coprecipitate raw material powder, a lithium compound, and a fluorine-containing compound are mixed and filled in the firing vessel provided with a dense ceramic coating layer having a silicon content of less than 5%. , A positive electrode active material powder made of fluorine-containing-nickel-lithium cobaltate that is fired in an oxygen-containing atmosphere at 600 to 1050 ° C. is included.
[0026]
Examples of the nickel-cobalt coprecipitate raw material powder include hydroxides, oxyhydroxides, and oxides. An example of the atomic ratio of nickel and cobalt is 0.8: 0.2. Further, about 10% of the number of moles of nickel and cobalt may be replaced with aluminum or manganese. Examples of the lithium compound include lithium hydroxide. An example of the fluorine-containing compound is lithium fluoride powder. The fluorine content of the lithium-containing nickel-cobalt composite oxide is exemplified by a molar ratio of 0.001 to 0.07 with respect to 2 atoms of oxygen in the lithium-containing composite oxide.
[0027]
Further, in the present invention, a nickel-cobalt-manganese coprecipitate raw material powder, a lithium compound, and a fluorine-containing compound are mixed in the firing container provided with a dense ceramic coating layer having a silicon content of less than 5%. A positive electrode active material powder made of fluorine-containing nickel-cobalt-lithium manganate that is filled and fired in an oxygen-containing atmosphere at 600 to 1050 ° C. is included.
[0028]
Examples of the nickel-cobalt-manganese coprecipitate raw material powder include hydroxides, oxyhydroxides, and oxides. An example of the atomic ratio of nickel, cobalt, and manganese is 1: 1: 1. The number of moles of nickel and manganese is preferably equimolar, and the number of moles of cobalt is preferably 0.1 to 0.4 moles relative to the total number of moles of nickel, cobalt and manganese.
[0029]
Further, about 10% of the total number of moles of nickel, cobalt and manganese may be replaced with aluminum or zirconium. Examples of the lithium compound include lithium carbonate powder and lithium hydroxide powder. An example of the fluorine-containing compound is lithium fluoride powder. The fluorine content of the lithium-containing nickel-cobalt-manganese composite oxide is exemplified by a molar ratio of 0.001 to 0.07 with respect to 2 atoms of oxygen in the lithium-containing composite oxide.
[0030]
Furthermore, the present invention also includes a lithium ion secondary battery including a positive electrode made of the various positive electrode active material powders described above.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described, but the present invention is not limited thereto.
[0032]
The positive electrode active material for a lithium ion secondary battery according to the present invention is a predetermined raw material powder, that is,
(1) Raw material powder containing cobalt compound powder, lithium carbonate powder and fluorine-containing compound powder,
(2) Raw material powder containing cobalt hydroxide powder and lithium carbonate powder,
(3) Nickel-cobalt coprecipitate raw material powder, raw material powder containing lithium compound and fluorine-containing compound,
(4) Nickel-cobalt-manganese coprecipitate raw material powder, raw material powder containing lithium compound and fluorine-containing compound,
Can be selected and fired in an atmosphere containing oxygen at 600 to 1050 ° C. in a firing container having a dense ceramic coating layer having a silicon content of less than 5% on the inner surface of the container substrate. .
[0033]
The positive electrode active material is preferably in the form of a spherical particle, and the average particle diameter is preferably 2 to 15 μm, particularly 3 to 9 μm. If the average particle size is smaller than 2 μm, it is difficult to form a dense electrode layer. Conversely, if it exceeds 15 μm, it is difficult to form a smooth electrode layer surface, which is not preferable.
[0034]
In the present invention, the oxygen atom of lithium cobaltate is partially substituted with a fluorine atom to improve battery safety. As content of fluorine, 0.00001-0.02 (more preferably 0.0005-0.005) fluorine is contained by oxygen atomic ratio. Examples of the fluorine-containing compound include lithium fluoride, ammonium fluoride, and aluminum fluoride.
[0035]
The fluorine-containing lithium cobalt oxide produced according to the present invention is preferable because the battery characteristics can be improved by substituting cobalt with 0.0001 to 1 mol%, if necessary, with another metal element. Examples of the substitution element include Zr, Mg, Ti, Al, Mn, and Sn.
[0036]
In the present invention, cobalt tetraoxide, cobalt oxyhydroxide, or cobalt hydroxide is used as the cobalt source. In particular, since the press density can be increased, it is preferable to use substantially spherical cobalt hydroxide or cobalt oxyhydroxide in which a large number of primary particles are aggregated to form secondary particles as a cobalt raw material. Here, the press density means that the powder is 0.32 t / cm. ² It means a numerical value obtained from the volume and powder weight when pressed at a pressure of.
[0037]
The specific surface area of the particulate positive electrode active material of the present invention is 0.2-1 m. ² / G is preferred. Specific surface area is 0.2m ² If it is smaller than / g, the discharge capacity per initial unit weight decreases, and conversely, 1 m ² Even when the amount exceeds / g, the discharge capacity per initial unit volume decreases, and the excellent positive electrode active material intended by the present invention cannot be obtained. Specific surface area is 0.3-0.7m ² / G is preferred.
[0038]
As the oxygen-containing atmosphere, an oxygen-containing atmosphere containing an oxygen concentration of preferably 10% by volume or more, particularly 40% by volume or more is preferable. By changing the type, mixed composition and firing conditions of each of the above raw materials, the excellent positive electrode active material targeted by the present invention can be obtained. As an example, preliminary firing can be performed in the firing. Pre-baking is preferably performed in an oxidizing atmosphere at 450 to 550 ° C., preferably 4 to 20 hours.
[0039]
A method for obtaining a positive electrode for a lithium ion secondary battery from the particulate positive electrode active material of the present invention can be carried out according to a conventional method. For example, a positive electrode mixture can be obtained by mixing a carbon-based conductive material such as acetylene black, graphite, and Ketchen black with a binder in the positive electrode active material powder of the present invention. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is used.
[0040]
A slurry in which the above positive electrode mixture is dispersed in a dispersion medium such as N-methylpyrrolidone is applied to a positive electrode current collector such as an aluminum foil, dried, and press-rolled to form a positive electrode active material layer on the positive electrode current collector. Form.
[0041]
In the lithium ion secondary battery using the positive electrode active material of the present invention for the positive electrode, a carbonate is preferable as the solvent of the electrolyte solution. Carbonates can be either cyclic or chain. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and the like.
[0042]
The carbonate ester may be used alone or in combination of two or more. Moreover, you may mix and use with another solvent. Depending on the material of the negative electrode active material, the combined use of a chain carbonate ester and a cyclic carbonate ester may improve the discharge characteristics, cycle durability, and charge / discharge efficiency.
[0043]
In addition, a vinylidene fluoride-hexafluoropropylene copolymer (for example, Kyner manufactured by Atchem Co.) or a vinylidene fluoride-perfluoropropyl vinyl ether copolymer is added to these organic solvents, and a gel polymer electrolyte is added by adding the following solute. It is also good.
[0044]
As the solute of the electrolyte solution, ClO ₄ -, CF ₃ SO ₃ -, BF ₄ -, PF ₆ -, AsF ₆ -, SbF ₆ -, CF ₃ CO ₂ -, (CF ₃ SO ₂ ) ₂ It is preferable to use at least one lithium salt having N- or the like as an anion. In the above electrolyte solution or polymer electrolyte, an electrolyte composed of a lithium salt is preferably added to the solvent or solvent-containing polymer at a concentration of 0.2 to 2.0 mol / L. If it deviates from this range, the ionic conductivity is lowered, and the electrical conductivity of the electrolyte is lowered. More preferably, 0.5 to 1.5 mol / L is selected. A porous polyethylene, a porous polypropylene film, etc. are used for a separator.
[0045]
A material capable of occluding and releasing lithium ions is used for the negative electrode active material of the lithium ion secondary battery using the positive electrode active material of the present invention for the positive electrode. The material for forming the negative electrode active material is not particularly limited. For example, lithium metal, lithium alloy, carbon material, periodic table 14, oxides mainly composed of group 15 metals, carbon compounds, silicon carbide compounds, silicon oxide compounds, sulfides Examples include titanium and boron carbide compounds.
[0046]
As the carbon material, those obtained by pyrolyzing organic substances under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, scale-like graphite, and the like can be used. As the oxide, a compound mainly composed of tin oxide can be used. As the negative electrode current collector, copper foil, nickel foil or the like is used.
[0047]
There is no restriction | limiting in particular in the shape of the lithium ion secondary battery which uses the positive electrode active material in this invention. A sheet shape (so-called film shape), a folded shape, a wound-type bottomed cylindrical shape, a button shape, or the like is selected depending on the application.
[0048]
【Example】
Next, specific examples of the present invention and comparative examples thereof will be described.
[0049]
Example 1
After dry mixing a predetermined amount of cobalt oxyhydroxide powder, lithium carbonate powder and lithium fluoride having an average spherical particle diameter of 13 μm formed by agglomeration of 50 to 200 primary particles of 0.8 μm, 30 cm square, depth An 8 cm baking container was filled and baked at 950 ° C. for 14 hours in the air. No adhesion of the fired powder to the vessel wall of the fired container was observed. LiCoO ₂ The fluorine content of the fired powder consisting of was 0.1% by weight.
As a firing container, the molded body is made of mullite, and the inner surface of the molded body is first coated with mullite to a thickness of 100 μm by plasma spraying. ₂ MgO ₄ A firing vessel in which spinel was coated to a thickness of 100 μm by plasma spraying was used. The porosity of the spinel coating layer was 8%.
About the powder (positive electrode active material powder) after firing, the specific surface area determined by the nitrogen adsorption method of the powder is 0.45 m. ² The average particle diameter D50 determined by the laser scattering type particle size distribution system was 13.8 μm.
The fluorine-containing LiCoO thus obtained. ₂ Powder, acetylene black, and polytetrafluoroethylene powder were mixed at a weight ratio of 80/16/4, and kneaded and dried while adding toluene to produce a positive electrode plate having a thickness of 150 μm.
Then, 20 μm thick aluminum foil is used as the positive electrode current collector, 25 μm thick porous polypropylene is used as the separator, 500 μm thick metal lithium foil is used as the negative electrode, and nickel foil 20 μm is used as the negative electrode current collector. And 1M LiPF as the electrolyte ₆ A simple stainless steel sealed cell was assembled in an argon glove box using / EC + DEC (1: 1).
The two batteries were first charged at 25 ° C. with a load current of 75 mA per gram of the positive electrode active material to 4.3 V, and discharged to 2.75 V with a load current of 75 mA per gram of the positive electrode active material. Asked.
And about one battery, the charge / discharge cycle test was further performed 30 times. The other battery is charged at 4.3 V for 10 hours, disassembled in an argon glove box, the positive electrode sheet after charging is taken out, the positive electrode sheet is washed, punched out to a diameter of 3 mm, and aluminum together with EC. The capsule was sealed, heated at a rate of 5 ° C./min, and the heat generation starting temperature was measured with a scanning differential calorimeter.
As a result, the heat generation start temperature was 173 ° C. The initial discharge capacity at 25 ° C., 2.75 to 4.3 V, and a discharge rate of 0.5 C was 160.4 mAh / g. The capacity retention rate after 50 charge / discharge cycles was 83.9%.
The above firing container according to the present invention was repeatedly used 10 times, but no abnormalities such as welding of the fired powder, cracking of the fired container, cracking and peeling of the coating layer were observed.
[0050]
Example 2
In Example 1, cobalt oxyhydroxide, lithium carbonate, and lithium fluoride were used in the same manner as in Example 1 except that a mullite firing container provided with only an alumina plasma spray coating layer was used instead of spraying mullite and spinel. Were mixed, filled in a firing container and fired to produce a fluorine-containing lithium cobalt oxide.
Adhesion of the fired powder to the fired container was not observed. The fluorine content in the lithium cobalt oxide was 0.03% by weight. The alumina coating layer had a thickness of 100 μm and a porosity of 9%. The specific surface area determined by the nitrogen adsorption method of the powder after firing is 0.32 m. ² The average particle diameter D50 determined by a laser scattering particle size distribution analyzer was 12.5 μm. The initial discharge capacity at 25 ° C., 2.75 to 4.3 V, and a discharge rate of 0.5 C was 160.0 mAh / g. The heat generation starting temperature was 176 ° C. The capacity retention rate after 50 charge / discharge cycles was 82.0%.
When the same firing container was repeatedly used 10 times, a sign of partial peeling was observed in the alumina layer of the firing container after 6 times of use, but no cracking or cracking of the container was observed after 10 times.
[0051]
<Comparative example 1>
A positive electrode active material was produced in the same manner as in Example 1 except that a mullite molded container not coated with alumina, mullite or spinel was used, and composition analysis, physical property measurement, and battery performance test were performed. The porosity of the mullite molded container was 25%. As a result of firing, the fired powder was welded to the molded container and could not be discharged.
[0052]
<Comparative example 2>
As a result of performing a firing test in the same manner as in Example 1 except that a pure alumina molded container was used instead of the mullite molded container of Comparative Example 1, the alumina molded container was damaged during firing.
[0053]
Example 3
A predetermined amount of cobalt hydroxide powder having an average spherical particle diameter of 13 μm formed by agglomeration of 50 to 200 primary particles of 0.6 μm and lithium carbonate powder are dry-mixed in a predetermined amount, and then a firing container of 30 cm square and 8 cm depth. The mixed powder was filled and fired at 950 ° C. for 14 hours in the air.
As in Example 1, the firing container was a molded body made of mullite, and the inner surface of the molded body was first coated with mullite to a thickness of 100 μm by plasma spraying, and further Al ₂ MgO ₄ A spinel having a thickness of 100 μm coated by plasma spraying was used (the porosity of the spinel coating layer was 8%).
About the powder (positive electrode active material powder) after baking, the specific surface area calculated | required by the nitrogen adsorption method of powder is 0.37 m ² The average particle diameter D50 determined by a laser scattering type particle size distribution system was 11.8 μm. As a result of quantifying the content of cobalt trioxide in the powder after firing by a powder X-ray diffraction method using Cu-Kα rays, the content of cobalt trioxide was 0.2% by weight or less.
LiCoO obtained in this way ₂ Powder, acetylene black and polytetrafluoroethylene powder were mixed at a weight ratio of 80/16/4, kneaded while adding toluene, and dried to prepare a positive electrode plate having a thickness of 150 μm.
Then, 20 μm thick aluminum foil is used as the positive electrode current collector, 25 μm thick porous polypropylene is used as the separator, 500 μm thick metal lithium foil is used as the negative electrode, and nickel foil 20 μm is used as the negative electrode current collector. And 1M LiPF as the electrolyte ₆ A simple stainless steel sealed cell was assembled in an argon glove box using / EC + DEC (1: 1).
The battery was first charged to 25 V at a load current of 75 mA per gram of the positive electrode active material at 25 ° C. and discharged to 2.75 V at a load current of 75 mA per gram of the positive electrode active material to obtain an initial discharge capacity. Furthermore, the charge / discharge cycle test was performed 50 times. The initial discharge capacity at 25 ° C., 2.75 to 4.3 V, and a discharge rate of 0.5 C was 160.4 mAh / g. The capacity retention rate after 50 charge / discharge cycles was 86.9%.
The above firing container according to the present invention was repeatedly used 10 times, but no abnormalities such as cracking, cracking and peeling of the coating layer were observed in the firing container, and the content of cobalt tetroxide in lithium cobaltate was 0.2% by weight or less. Met.
[0054]
Example 4
In Example 3, except that spinel was not sprayed and a mullite firing container provided with only an alumina spray coating layer was used, as in Example 3, cobalt hydroxide and lithium carbonate were mixed and filled in the firing container. Then, lithium cobaltate was produced by firing. The content of cobalt tetroxide in lithium cobaltate was 0.2% by weight or less. The alumina coating layer had a thickness of 100 μm and a porosity of 9%.
The specific surface area determined by the nitrogen adsorption method of the powder after firing is 0.32 m. ² The average particle diameter D50 determined by a laser scattering type particle size distribution meter was 12.5 μm. The initial discharge capacity at 25 ° C., 2.75 to 4.3 V, and a discharge rate of 0.5 C was 160.0 mAh / g. The capacity retention rate after 50 charge / discharge cycles was 92.0%.
When the same baking container was repeatedly used 10 times, in all cases, the content of cobalt tetroxide in the lithium cobalt oxide was 0.2% by weight or less. After 10 times of use, some signs of peeling were observed in the alumina layer of the firing container, but no cracks or cracks were observed in the container.
[0055]
<Comparative Example 3>
LiCoO was prepared in the same manner as in Example 3 except that a mullite molded container not coated with alumina or spinel was used. ₂ A positive electrode active material was produced, and composition analysis, physical property measurement and battery performance test were performed. The porosity of the mullite molded container was 25%. As a result of the firing, the content of cobalt tetroxide in the produced lithium cobaltate was 8.6%.
Moreover, the specific surface area calculated | required by the nitrogen adsorption method of the powder after baking is 0.46 m. ² The average particle size D50 determined by a laser scattering particle size distribution analyzer was 13.3 μm. The initial discharge capacity at 25 ° C., 2.75 to 4.3 V, and a discharge rate of 0.5 C was 140.5 mAh / g. The capacity retention rate after 50 charge / discharge cycles was 79.4%.
[0056]
<Comparative example 4>
As a result of performing a firing test in the same manner as in Example 4 except that a pure alumina molded container was used instead of the mullite molded container, the alumina container was damaged during firing.
[0057]
Example 5
To the mixed aqueous solution of nickel sulfate, cobalt sulfate and manganese sulfate, ammonia and caustic soda aqueous solution are added to synthesize a coprecipitated hydroxide, filtered, dried and calcined at 500 ° C. Synthesized.
Lithium carbonate powder and lithium fluoride powder were added to and mixed with this, and the same baking container as used in Example 1 (that is, a molded body made of mullite as a substrate was used. Is coated by plasma spraying to a thickness of 100 μm, and Al ₂ MgO ₄ A firing container in which spinel is coated to a thickness of 100 μm by plasma spraying, and the spinel coating layer has a porosity of 8%. ) And then pulverized after firing in an atmosphere containing 40% oxygen at 900 ° C. for 15 hours. Abnormalities such as adhesion of the fired powder to the fired container were not observed.
As a result of analyzing the calcined powder, LiNi _1/3 Co _1/3 Mn _1/3 O _1.97 F _0.03 Met. Average particle size is 10.2 μm, specific surface area is 0.8 m ² / G. As a result of evaluating the battery performance in the same manner as in Example 1, the discharge capacity was 163 mAh / g, the capacity retention after 50 cycles was 96%, and the heat generation start temperature was 255 ° C.
[0058]
【The invention's effect】
As described above, according to the present invention, a positive electrode active material powder made of a lithium-containing composite oxide using a firing container having a dense ceramic coating layer having a silicon content of less than 5% on the inner surface of the container substrate. The positive electrode active material powder with a small impurity content can be obtained by firing the raw material powder. Moreover, in the positive electrode active material powder containing a fluorine compound, since the fluorine-containing compound does not weld to the firing container during firing, it can be easily taken out from the firing container.

Claims (11)

In a firing container for a positive electrode active material powder used when firing a predetermined raw material powder to obtain a positive electrode active material powder comprising a lithium-containing composite oxide,
A firing container for a positive electrode active material powder, characterized in that a dense ceramic coating layer having a silicon content of less than 5% is provided on the inner surface of a container substrate. The firing container for positive electrode active material powder according to claim 1, wherein the ceramic coating layer is made of at least one of spinel and alumina. The firing container for positive electrode active material powder according to claim 1 or 2, wherein the ceramic coating layer has a porosity of 15% or less. The firing container for positive electrode active material powder according to claim 1, wherein the ceramic coating layer has a thickness of 50 to 500 μm. The firing container for positive electrode active material powder according to any one of claims 1 to 4, wherein the spinel constituting the ceramic coating layer is Al ₂ MgO ₄ . The firing container for positive electrode active material powder according to any one of claims 1 to 5, wherein the container substrate is mullite or cordierite. In the firing container according to any one of claims 1 to 6, a cobalt compound powder, a lithium carbonate powder and a fluorine-containing compound powder are mixed and filled, and fired in an oxygen-containing atmosphere at 600 to 1050 ° C. A positive electrode active material powder comprising a fluorine-containing lithium cobalt oxide. The firing container according to any one of claims 1 to 6, wherein cobalt hydroxide powder and lithium carbonate powder are mixed and filled, and fired in an oxygen-containing atmosphere at 600 to 1050 ° C. A positive electrode active material powder composed of lithium cobalt oxide. In the firing container according to any one of claims 1 to 6, a nickel-cobalt coprecipitate raw material powder, a lithium compound and a fluorine-containing compound are mixed and filled, and an oxygen-containing atmosphere at 600 to 1050 ° C is filled. A positive electrode active material powder made of fluorine-containing nickel-lithium cobaltate, which is fired. The firing container according to any one of claims 1 to 6, wherein nickel-cobalt-manganese coprecipitate raw material powder, a lithium compound and a fluorine-containing compound are mixed and filled, and an oxygen-containing atmosphere at 600 to 1050 ° C. A positive electrode active material powder made of fluorine-containing nickel-cobalt-lithium manganate, which is fired underneath. A lithium ion secondary battery comprising a positive electrode comprising the positive electrode active material powder according to any one of claims 7 to 10.