JPH11292547A - Lithium cobaltate, its production and lithium cell using that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lithium cobaltate having large particle volume and large particle size with little sintering. SOLUTION: A bivalent cobalt compd. is reacted with an alkali hydroxide and an ammonium compd. showing alkalinity in a water-based medium to produce cobalt hydroxide, and then the obtd. cobalt hydroxide is mixed with a lithium compd. and calcined. Or, a bivalent cobalt compd. is reacted with an alkali hydroxide and an ammonium compd. showing alkalinity in a water-based medium to produce cobalt hydroxide, and then the obtd. cobalt hydroxide is calcined to obtain tricobalt tetroxide, and then the obtd. tricobalt tetroxide is mixed with a lithium compd. and then calcined. A lithium cell using the obtd. lithium cobaltate as a positive pole active material has high initial discharge capacity and excellent cycle characteristics of average charge and discharge efficiency and discharge capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium cobalt oxide useful as a positive electrode active material of a lithium secondary battery, a method for producing the same, and a lithium battery using the same.

[0002]

2. Description of the Related Art With the rapid expansion of small electronic devices such as personal computers and mobile phones in recent years, the demand for lithium secondary batteries has been rapidly increasing, and lithium cobalt oxide has been mainly used as a positive electrode active material. I have. In general, when lithium cobalt oxide is used as a positive electrode active material of a lithium secondary battery, the smaller the particle size of lithium cobalt oxide, the better the charge / discharge characteristics at a high current density, but the stability tends to deteriorate. Therefore, in practice, particles having various particle sizes are used depending on the balance between these characteristics and the application and configuration of the battery. However, it is considered that it is desirable that the lithium cobalt oxide particles be in a single crystal and close to a monodispersed state at any particle size. Such a lithium cobalt oxide is prepared by mixing a powder of a cobalt compound such as cobalt hydroxide, tricobalt tetroxide, or cobalt carbonate with a powder of a lithium compound such as lithium carbonate or lithium hydroxide in a dry system, and then mixing the mixture with a powder of 600 to 1100. It is manufactured industrially through a process of firing at a temperature of about ° C and then pulverizing. Of course, the properties of the obtained lithium cobalt oxide are affected by the conditions of these production steps, but the particle properties of cobalt hydroxide and cobalt oxide used as the cobalt raw material are also greatly affected by the properties of lithium cobalt oxide. Have an effect.

[0003] The following method is known as a method for producing cobalt hydroxide and cobalt oxide used as a cobalt raw material in producing lithium cobalt oxide. A method of reacting an equivalent or more of alkali hydroxide with a divalent cobalt salt aqueous solution or a divalent cobalt double salt slurry to obtain a precipitate of cobalt hydroxide, washing the obtained cobalt hydroxide with water, drying, and then 300 to 900 ° C. To obtain tricobalt tetroxide by firing at a temperature of
No. 25052). Further, Japanese Patent Application Laid-Open No. 9-22692 describes a method of obtaining a cobalt hydroxide having a plate-like shape with a fixed direction diameter of 0.1 to 10 μm, followed by firing at a temperature of 200 to 700 ° C. . Further, Japanese Unexamined Patent Publication No.
JP-A-91018 and JP-A-8-96809 also describe a method for producing tricobalt tetroxide via a cobalt carbonate.

[0004] Cobalt hydroxide and cobalt oxide obtained by the above method are used as a cobalt raw material, and powders of lithium compounds such as lithium carbonate and lithium hydroxide are mixed in a dry system, and then mixed at about 600 to 1100 ° C. To obtain lithium cobalt oxide.

[0005]

The lithium cobalt oxide obtained by the above-mentioned prior art is fine particles of 0.5 μm or less, or the particle diameter in the bottom direction is large, but the thickness in the end surface direction is zero. Often less than 2 μm,
There is a problem that only particles having a small volume can be obtained. In order to obtain large particles of lithium cobalt oxide using cobalt hydroxide and tricobalt tetroxide obtained by conventional techniques as raw materials, the particles must be grown by firing at a high temperature in a firing step. There is a problem that the particles are strongly fixed to each other or the particles are sintered. Furthermore, the degree of pulverization must be strengthened in order for such particles to adhere to each other or to make the sintered particles closer to a monodispersed state. However, there is a problem that the characteristics are deteriorated.

[0006]

In order to develop lithium cobalt oxide having a large particle volume, a large particle size and low sintering, the present inventors have developed a raw material such as cobalt hydroxide and tetraoxide. As a result of intensive studies on the improvement of tricobalt, the average particle diameter of the bottom surface is 1 to 30 μm, the average particle height is 0.2 to 10 μm, the particle shape is a hexagonal column, the particle volume is large and large. That lithium cobalt oxide having a diameter is obtained, and in an aqueous medium, a cobalt compound is obtained by reacting a divalent cobalt compound, an alkali hydroxide, and an ammonium compound exhibiting alkalinity,
Then, the obtained cobalt hydroxide is mixed with a lithium compound and then calcined, or, in an aqueous medium, reacted with a divalent cobalt compound, an alkali hydroxide, or an ammonium compound exhibiting alkalinity to form cobalt hydroxide. And then calcining the obtained cobalt hydroxide to obtain tricobalt tetroxide, followed by mixing and calcination of the obtained tricobalt tetroxide and a lithium compound, thereby obtaining the above cobalt acid. That lithium can be obtained,
Furthermore, they have found that such lithium cobalt oxide is suitable as a positive electrode active material of a lithium battery, and have completed the present invention.

That is, an object of the present invention is to provide a lithium cobalt oxide having a large particle volume and a large particle diameter, a method for producing the same, and a lithium battery using the same.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the average particle diameter of the bottom surface is 1
Lithium cobaltate characterized by having a particle size of up to 30 μm, an average particle height of 0.2 to 10 μm, and a hexagonal column shape. In the present invention, the hexagonal prism shape is
Most particles have a hexagonal bottom surface, and some particles may have a bottom surface other than hexagonal shape. In the present invention, the average particle diameter of the bottom surface (the average value of the length of the longest diagonal line of the hexagonal bottom surface of the particles) is 1 to 30 μm, and preferably 1.5 to 30 μm.
m, more preferably 2 to 20 μm. Furthermore, the average particle height (the average value of the thickness of the particles in the end face direction) is 0.2 to
It is 10 μm, preferably 0.3 to 10 μm, more preferably 0.5 to 10 μm. If the average particle diameter and the average particle height of the bottom face are smaller than the above ranges, the stability of a lithium battery using the same as an electrode is unfavorably deteriorated. In addition, there is a correlation between the particle volume and the specific surface area of lithium cobalt oxide unless the interparticle sintering is performed, such that the larger the particle volume, the smaller the specific surface area. However, if there is interparticle sintering, a factor is added to the correlation between the particle volume and the specific surface area that the larger the degree of interparticle sintering, the smaller the specific surface area. As a result, even when lithium cobaltate having the same specific surface area is used, the particle volume without interparticle sintering is larger than that with interparticle sintering. Lithium cobaltate of the present invention has less inter-particle sintering, and has the same specific surface area as compared to many inter-particle sintering,
The volume of individual particles is large.

Next, the present invention relates to a method for producing lithium cobalt oxide, which comprises the following steps: 1) reacting a divalent cobalt compound, an alkali hydroxide, and an ammonium compound exhibiting alkalinity in an aqueous medium to produce cobalt hydroxide; And then calcining after mixing the obtained cobalt hydroxide and a lithium compound, followed by baking. Further, 2) a divalent cobalt compound and a hydroxide Alkali, reacting with an ammonium compound exhibiting alkalinity to obtain cobalt hydroxide,
Then, the obtained cobalt hydroxide is calcined to obtain tricobalt tetroxide, and then, the obtained tricobalt tetroxide is mixed with a lithium compound, followed by calcination, followed by calcination. is there. The mechanism by which such a method produces lithium cobalt oxide having a large particle volume and a large particle diameter is not clear, but is presumed as follows. First, it is considered that the cobalt compound reacts with the ammonium compound exhibiting alkalinity to form a complex compound containing ammonia as an intermediate. This compound is ultimately converted to cobalt hydroxide by an alkali containing at least an alkali hydroxide. However, this conversion reaction proceeds very slowly, so that conditions under which the particle growth reaction becomes dominant are taken. It is thought that it is easy. By calcining the thus obtained cobalt hydroxide having a large particle volume and a large particle diameter,
It is considered that the cobalt hydroxide is converted to tricobalt tetroxide while maintaining the particle shape. Furthermore, a large particle volume of cobalt hydroxide of a large particle size, tricobalt tetroxide and a lithium compound are mixed and then calcined to form cobalt cobalt oxide and tricobalt tetroxide into lithium cobalt oxide while maintaining the particle shape. It is considered to be converted.

[0010] As the divalent cobalt compound used in the production method of the present invention, cobalt sulfate, cobalt chloride, cobalt nitrate and the like can be used.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide and the like can be used. The amount of the alkali hydroxide is 0.1 to the divalent cobalt compound.
It is 5 to 1.5 equivalents, preferably 0.7 to 1.3 equivalents, more preferably 0.8 to 1.2 equivalents. If the amount of the alkali hydroxide is less than the above range, the ammonia-containing complex compound is not converted to cobalt hydroxide or it takes an extremely long time, which is not preferable. Further, when the amount is larger than the above range, the conversion from the ammonia-containing complex compound to cobalt hydroxide is too fast to generate fine particles, and even when large particles are generated, the shape thereof is preferably a thin plate-like particle, which is preferable. Absent.

Further, the ammonium compound exhibiting alkalinity is an ammonium compound exhibiting alkalinity when present in an aqueous medium, such as ammonia gas,
Ammonia water, ammonium carbonate, or the like can be used. A neutral or acidic ammonium compound such as ammonium sulfate, ammonium chloride, and ammonium nitrate is not preferable because an ammonia-containing complex compound is not easily formed. The amount of the ammonium compound is 0.5 to 1.5 equivalents, preferably 0.6 to 1.2 equivalents, more preferably 0.7 to 1.1 equivalents to the divalent cobalt compound. If the amount of the ammonium compound is less than the above range, the ammonia-containing complex compound, which is an intermediate product, has a small ammonia content, so that the conversion reaction to cobalt hydroxide is accelerated, and fine particles are easily generated, which is not preferable. On the other hand, if the amount is larger than the above range, the amount of ammonia in the reaction system increases, so that the conversion reaction to cobalt hydroxide is undesirably slow.

The reaction temperature is 0 to 80 ° C., preferably 5 to 80 ° C.
It is preferable to carry out at a temperature of 60 ° C, more preferably 10 to 40 ° C. If the reaction temperature is high, there is an effect on the shape surface such as an increase in the particle diameter in the bottom direction, and there is an effect on the production surface such as the growth rate can be increased, but if the reaction temperature is higher than the above range, the thickness of the particles becomes thin, It is not preferable because particles having a large volume are not generated. In addition, even if it is lower than the above range, there is almost no difference in shape from the product when reacted at around 0 ° C.,
It is not preferable because it is industrially disadvantageous such that it takes a long time to grow.

This reaction is preferably carried out in an atmosphere of an inert gas such as nitrogen in order to prevent oxidation of the divalent cobalt compound in the aqueous medium. If a trivalent cobalt compound is generated during the reaction, it is not converted into cobalt hydroxide, which is a divalent cobalt compound, so that a mixture of divalent cobalt hydroxide and a trivalent cobalt compound is finally obtained. Is not preferred because

In order to react a divalent cobalt compound, an alkali hydroxide and an alkaline ammonium compound in an aqueous medium, specifically, a divalent cobalt compound, an alkali hydroxide and an alkaline ammonium compound are mixed with an aqueous compound. A method of adding and reacting at the same time in a medium, in an aqueous medium containing a divalent cobalt compound,
A method in which an alkali hydroxide and an ammonium compound exhibiting alkalinity are added at the same time to cause a reaction, and a reaction is performed by simultaneously adding a divalent cobalt compound and an alkali hydroxide to an aqueous medium containing an ammonium compound exhibiting alkalinity. A method of adding a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity to an aqueous medium to obtain a reaction product, and then reacting the obtained reaction product with an alkali hydroxide. Reacting a divalent cobalt compound with an ammonium compound exhibiting alkalinity in an aqueous medium,
Next, the reaction can be performed by a method of reacting the obtained reaction product with an alkali hydroxide.

In the above methods (1) to (3), the addition time of the divalent cobalt compound, alkali hydroxide and ammonium compound exhibiting alkalinity can be appropriately set, but is usually 10 minutes to 24 hours, preferably 30 minutes to 20 hours, more preferably It is good to carry out for 1 hour to 15 hours. Addition within the above-mentioned time period is preferable because the generation of fine particles can be prevented and cobalt hydroxide can be obtained under the predominant conditions of particle growth. If the addition time is shorter than the above range, the generation of fine particles becomes remarkable, which is not preferable. If the addition time is made longer, the particles become larger. However, if the addition time is longer than the above range, the reaction time becomes longer, and the effect of making the particles larger is not recognized so much. Also, adding two or three kinds of a divalent cobalt compound, an alkali hydroxide and an alkaline ammonium compound at the same time means that the divalent cobalt compound, the alkali hydroxide and the alkaline ammonium compound are reacted during the reaction period. Means that each of them is present in the reaction system.Specifically, the respective predetermined amounts are added in parallel or continuously, intermittently, or after adding one or two types. Or the addition of species that remain in a short time. In the present invention, it is preferable to add a divalent cobalt compound and an alkali hydroxide in the presence of at least a part of a predetermined amount of an ammonium compound exhibiting alkalinity, or at the same time as the ammonium compound.

The above-mentioned methods are primary methods,
Is a method in which a predetermined amount of a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity are added to an aqueous medium at the same time and reacted.
Is a method in which a predetermined amount of an alkali hydroxide and an ammonium compound exhibiting alkalinity are added at the same time to an aqueous medium containing a predetermined amount of a divalent cobalt compound to cause a reaction. This is a method in which a predetermined amount of a divalent cobalt compound and a predetermined amount of an alkali hydroxide are simultaneously added to an aqueous medium containing a predetermined amount of an ammonium compound to be reacted.

On the other hand, the above method is a sequential method. In the method, first, predetermined amounts of a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity are added to an aqueous medium. (A specific method of addition is preferably according to the above-mentioned methods.),
A method of obtaining a reaction product and then reacting the obtained reaction product with an alkali hydroxide.In the method, first, in an aqueous medium, a divalent cobalt compound and an ammonium compound exhibiting alkalinity are mixed. The reaction is carried out (preferably, the reaction is carried out by adding or containing a divalent cobalt compound and an ammonium compound according to the above-mentioned methods) and then obtained. This is a method of reacting a reaction product with an alkali hydroxide. The method of reacting the obtained reaction product with alkali hydroxide in the method of the above, adding alkali hydroxide to the slurry of the reaction product, or reacting the reaction product in an aqueous medium solution of alkali hydroxide Or the addition of a slurry of a reaction product and an alkali hydroxide in an aqueous medium at the same time. In this reaction, an alkaline ammonium compound may be present in the alkali hydroxide.

The cobalt hydroxide thus obtained may be aged, filtered, washed,
It may be dried. Drying is preferably performed in an atmosphere of an inert gas such as nitrogen gas so as not to oxidize.

Next, the cobalt hydroxide thus obtained is calcined to obtain tricobalt tetroxide. This calcination is an oxidation reaction and a dehydration reaction from cobalt hydroxide having a valence of divalent cobalt to tricobalt tetroxide having an average valence of 2.67, and requires oxygen. It takes place in the atmosphere. The firing temperature is 200-700 ° C
And preferably at 250 to 600 ° C. If the firing temperature is lower than the above range, the oxidation reaction and the dehydration reaction hardly occur, which is not preferable. On the other hand, if it is higher than the above range, the hexagonal columnar shape is broken, and granular tricobalt tetroxide is generated, which is not preferable.

Next, the cobalt hydroxide or tricobalt tetroxide obtained as described above is mixed with a lithium compound and then calcined to obtain the lithium cobalt oxide of the present invention. The lithium compound to be used is not particularly limited, but lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate and the like can be used. Also,
The mixing ratio of cobalt hydroxide or tricobalt tetroxide to the lithium compound is 0.9 to 0.9 in Co / Li (molar ratio).
A range of 1.1 is preferred. To mix cobalt hydroxide or tricobalt tetroxide with a lithium compound, a conventional dry mixing or wet mixing method can be used. Next, a firing temperature for firing a mixture of cobalt hydroxide or tricobalt tetroxide and a lithium compound is 600.
The temperature is preferably 1 to 1100 ° C., and the firing atmosphere is not particularly limited as long as it is an oxidizing atmosphere such as the air.

The thus obtained lithium cobaltate may be pulverized by a pulverizer such as a sample mill if necessary.

Next, the present invention is a positive electrode for a lithium battery comprising the above-mentioned lithium cobalt oxide, and further a lithium battery using the positive electrode. Note that a lithium battery in the present invention is a primary battery using lithium metal for the negative electrode, a rechargeable secondary battery using lithium metal for the negative electrode, and a chargeable / dischargeable battery using a carbon material or tin compound for the negative electrode. Lithium ion secondary battery.

When the positive electrode for a lithium battery is to be used for a coin-type battery, the lithium cobalt oxide of the present invention may be added to a carbon-based conductive agent such as acetylene black, carbon or graphite powder, a polytetrafluoroethylene resin or a polytetrafluoroethylene resin. It can be obtained by adding a binder such as vinylidene fluoride, kneading, and pelletizing. Furthermore, in the case of a cylindrical or prismatic battery, an organic solvent such as N-methylpyrrolidone is also added to the lithium cobaltate of the present invention in addition to these additives, and the mixture is kneaded into a paste to form an aluminum foil. It can be obtained by coating on such a metal current collector and drying.

In the electrolyte of a lithium battery, lithium ions are dissolved in a polar organic solvent which is electrochemically stable, that is, which is not oxidized or reduced in a wider range than the potential range in which the lithium ion battery operates. You can use the one you let. As the polar organic solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, tetrahydrofuran, γ-butyllactone, or a mixture thereof can be used. Solutes that serve as lithium ion sources include lithium perchlorate and lithium hexafluorophosphate,
Lithium tetrafluoroborate or the like can be used.
A porous polypropylene film or polyethylene film is disposed between the electrodes as a separator.
As for the type of battery, a separator is placed between the positive and negative electrodes in the form of pellets, pressed into a sealing can with a gasket made of polypropylene, injected with electrolyte, and sealed, coin-type, and a positive electrode material or negative electrode. The material may be coated on a metal current collector, wound up with a separator, inserted into a battery can with a gasket, injected with an electrolyte, and sealed, and may be a cylindrical type. There is also a three-electrode type battery particularly for measuring electrochemical properties. In this battery, a reference electrode is disposed in addition to the positive electrode and the negative electrode, and the electrochemical characteristics of each electrode are evaluated by controlling the potential of another electrode with respect to the reference electrode.

Regarding the performance of lithium cobalt oxide as a positive electrode active material, a lithium battery was constructed by the above-described method.
It can be evaluated by charging and discharging an appropriate potential range with a constant current and measuring the electric capacity. In addition, the quality of the cycle characteristics can be determined from the change in the electric capacity due to the repeated charge and discharge.

[0027]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 In 500 ml of pure water adjusted to a temperature of 20 ° C., 1 liter of an aqueous solution of cobalt sulfate having a divalent cobalt ion concentration of 60 g / l and 17% ammonia water were added so that the pH of the reaction solution was maintained at 8. Ammonia-containing complex compound slurry was prepared by parallel addition in 3 hours, and then, while maintaining the temperature of the slurry at 20 ° C., an aqueous solution of sodium hydroxide having a concentration of 400 g / l was added in 3 hours to adjust the pH to 12. After aging for one day, cobalt hydroxide was obtained. The amounts of ammonia and sodium hydroxide used were 0.9 equivalent and 1.0 equivalent, respectively, relative to cobalt. These operations were performed in a nitrogen gas atmosphere. Thereafter, the slurry containing cobalt hydroxide was filtered, washed, and dried at a temperature of 120 ° C. to obtain a cobalt hydroxide powder (sample a). Further, the above-mentioned cobalt hydroxide powder (sample a) and lithium carbonate were mixed so that the Co / Li ratio was 1/1 (molar ratio).
After firing for 0 hours, the powder was pulverized by a sample mill to obtain a lithium cobaltate powder (sample A) of the present invention.

Example 2 The cobalt hydroxide powder (sample a) obtained in Example 1 was calcined in air at 300 ° C. to obtain tricobalt tetroxide powder (sample b). The cobalt trioxide powder (sample b) and lithium carbonate were mixed at a Co / Li ratio of 1/1 (molar ratio).
And calcined in air at 900 ° C. for 10 hours, and then pulverized by a sample mill to obtain a lithium cobaltate powder (sample B) of the present invention.

Example 3 To 700 ml of 5% aqueous ammonia adjusted to a temperature of 30 ° C., 1 liter of an aqueous solution of cobalt sulfate having a divalent cobalt ion concentration of 60 g / l and 200 ml of an aqueous solution of sodium hydroxide having a concentration of 400 g / l for 6 hours. After the addition in parallel, the mixture was aged for 3 days to obtain cobalt hydroxide. The pH of the slurry was 12 during aging. The amounts of ammonia and sodium hydroxide used were 1.0 equivalent to cobalt, respectively.
1.0 equivalent. These operations were performed in a nitrogen gas atmosphere. Thereafter, the slurry containing cobalt hydroxide was filtered, washed, and dried at a temperature of 120 ° C. to obtain a cobalt hydroxide powder (sample c). Further, the above-mentioned cobalt hydroxide powder (sample c) and lithium carbonate were mixed so that the Co / Li ratio was 1/1 (molar ratio), and the mixture was fired in air at 900 ° C. for 10 hours. To obtain a lithium cobaltate powder of the present invention (Sample C).

Example 4 The cobalt hydroxide powder (sample c) obtained in Example 3 was calcined at 300 ° C. in air to obtain tricobalt tetroxide powder (sample d). Cobalt tetroxide powder (sample d) and lithium carbonate were mixed at a Co / Li ratio of 1/1 (molar ratio).
And calcined in air at 900 ° C. for 10 hours, and then pulverized with a sample mill to obtain a lithium cobaltate powder (Sample D) of the present invention.

Example 5 1 liter of an aqueous solution of cobalt sulfate having a divalent cobalt ion concentration of 60 g / l was adjusted to a temperature of 20 ° C., and 150 ml of a 17% aqueous ammonia solution was added until the pH of the aqueous solution reached 8.
A mixed solution of 50 g of an aqueous sodium hydroxide solution having a concentration of 0 g / l was added to form an ammonia-containing complex compound slurry. The pH was adjusted to 12 by adding 150 ml of an aqueous solution of sodium hydroxide having a concentration of 6 over 6 hours, and the mixture was aged for 2 days to obtain cobalt hydroxide. The amounts of ammonia and sodium hydroxide used were each 0.1 to cobalt.
9 equivalents and 1.0 equivalents. These operations were performed in a nitrogen gas atmosphere. Thereafter, the slurry containing the cobalt hydroxide was filtered, washed, and then cooled to 120 ° C.
, To obtain a cobalt hydroxide powder (sample e). Further, the cobalt hydroxide powder (sample e) and lithium carbonate were mixed so that the Co / Li ratio was 1/1 (molar ratio), and the mixture was fired in air at 900 ° C. for 10 hours. To obtain a lithium cobaltate powder of the present invention (Sample E).

Example 6 The cobalt hydroxide powder (sample e) obtained in Example 5 was calcined in air at a temperature of 300 ° C. to obtain tricobalt tetroxide powder (sample f). The above-mentioned tricobalt tetroxide powder (sample f) and lithium carbonate were mixed at a Co / Li ratio of 1/1 (molar ratio).
And calcined in air at 900 ° C. for 10 hours, and then pulverized with a sample mill to obtain a lithium cobaltate powder (Sample F) of the present invention.

Comparative Example 1 One liter of an aqueous solution of cobalt sulfate having a divalent cobalt ion concentration of 60 g / l was mixed with 500 ml of pure water adjusted to a temperature of 20 ° C.
Then, 00 g / l sodium hydroxide was added in parallel for 3 hours so that the pH of the reaction solution was maintained at 12, followed by aging for 1 day to obtain cobalt hydroxide. The amount of sodium hydroxide used was 1.1 equivalents relative to cobalt.
These operations were performed in a nitrogen gas atmosphere. Thereafter, the slurry containing the cobalt hydroxide was filtered, washed, and dried at a temperature of 120 ° C. to obtain a cobalt hydroxide powder (sample g). Further, the cobalt hydroxide powder (sample g) and lithium carbonate were mixed at a Co / Li ratio =
Mix at 1/1 (molar ratio), 900 ° C in air
After sintering at a temperature of 10 hours, the mixture was pulverized with a sample mill to obtain lithium cobaltate powder (sample G).

Comparative Example 2 The cobalt hydroxide powder (sample g) obtained in Comparative Example 1 was calcined in air at a temperature of 300 ° C. to obtain tricobalt tetroxide powder (sample h). Cobalt tetroxide powder (sample h) and lithium carbonate were mixed at a Co / Li ratio of 1/1 (molar ratio).
And calcined in air at 900 ° C. for 10 hours, and then pulverized by a sample mill to obtain a lithium cobaltate powder (Sample H) of the present invention.

The specific surface area of the lithium cobalt oxide (samples A to H) obtained in Examples 1 to 6 and Comparative Examples 1 and 2 by the BET method, the average particle diameter of the bottom surface read from an electron micrograph, and the average particle height The results are shown in Table 1. 1 and 2 show electron micrographs of Sample A of Example 1 and Sample G of Comparative Example 1, respectively. Table 1 and FIGS.
Thus, the lithium cobaltate of the present invention has a large average particle diameter and a large average particle height on the bottom surface, a large particle volume, and further, the particle shape on the bottom surface is substantially hexagonal, and the particle shape is a hexagonal column shape. I understood. In addition, it was found that the lithium cobaltate of the present invention had low interparticle sintering and good dispersibility. On the other hand, it was found that the lithium cobalt oxide of the comparative example had remarkable sintering between particles.

[0037]

[Table 1]

Next, the charge / discharge characteristics and the cycle characteristics of the lithium secondary batteries using the samples A to H as the positive electrode active materials were evaluated. The battery was a three-electrode cell, and charging and discharging were repeated. The form and measurement conditions of the battery will be described.

Each of the above samples, graphite powder as a conductive agent, and polytetrafluoroethylene resin as a binder were mixed at a weight ratio of 3: 2: 1 and kneaded in an agate mortar to form a circle having a diameter of 14 mm. It was molded into a pellet.
The weight of the pellet was 50 mg. This was sandwiched between metal titanium meshes and pressed at a pressure of 150 kg / cm ² to obtain a positive electrode.

On the other hand, metallic lithium having a thickness of 0.5 mm was formed into a circular shape having a diameter of 14 mm, sandwiched between metallic nickel meshes, and pressed to obtain a negative electrode. In addition, a metal lithium foil having a thickness of 0.1 mm was wound around a metal nickel wire to the extent that rice grains were large, and this was used as a reference electrode. As the non-aqueous electrolyte, a mixed solution of 1,2-dimethoxyethane and propylene carbonate in which lithium perchlorate was dissolved at a concentration of 1 M (mixed at a volume ratio of 1: 1) was used. The electrodes are arranged in the order of positive electrode, reference electrode, negative electrode,
In the meantime, a porous polypropylene film was placed as a separator.

The measurement of the charge / discharge cycle is performed by setting the voltage range to 4.
From 3 V to 3.5 V, the charge / discharge current was 0.26 mA (about 1
(Cycles / day) at a constant current. Table 2 shows the average charge / discharge efficiency calculated from the initial discharge capacity and the discharge capacity at 10 cycles, and the cycle characteristics of the discharge capacity calculated from the discharge capacity at the 10th cycle. Capacity is 1g of positive electrode active material
It is around. From this table, it was found that the lithium battery using the lithium cobalt oxide of the present invention had a high initial discharge capacity, and was also excellent in average charge / discharge efficiency and cycle characteristics of the discharge capacity.

[0042]

[Table 2]

[0043]

According to the present invention, the average particle diameter of the bottom surface is from 1 to 30.
μm, and the average particle height is 0.2 to 10 μm, the lithium cobalt oxide characterized in that the particle shape is hexagonal column, lithium cobalt oxide with a large particle size and less interparticle sintering is there. A lithium battery using this as a positive electrode active material has excellent average charge / discharge efficiency and cycle characteristics of discharge capacity. Further, the present invention provides a cobalt hydroxide by reacting a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity in an aqueous medium, and then reacting the obtained cobalt hydroxide with a lithium compound. A method for producing lithium cobalt oxide characterized by firing after mixing, or, in an aqueous medium, a divalent cobalt compound, an alkali hydroxide, reacting with an ammonium compound exhibiting alkalinity to obtain cobalt hydroxide, Then, the obtained cobalt hydroxide is calcined to obtain tricobalt tetroxide, and then, the obtained tricobalt tetroxide is mixed with a lithium compound, followed by calcination, followed by calcination. This is a method by which lithium cobalt oxide having a large particle size can be efficiently obtained.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 10000) showing the particle structure of Sample A obtained in Example 1.

FIG. 2 is an electron micrograph (magnification: 10,000 times) showing the particle structure of Sample G obtained in Comparative Example 1.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuo Suzuki 1 Ishiharacho, Yokkaichi-shi, Mie Pref. Ishihara Sangyo Co., Ltd. (72) Inventor Yoshiaki Moriyama 1st Ishiharacho, Yokkaichi-shi, Mie Ishihara Sangyo Co., Ltd. Yokkaichi Office

Claims (10)

[Claims] 1. A lithium cobalt oxide having an average particle diameter at the bottom of 1 to 30 μm, an average particle height of 0.2 to 10 μm, and a hexagonal column shape. 2. In an aqueous medium, a divalent cobalt compound, an alkali hydroxide, and an ammonium compound exhibiting alkalinity are reacted to obtain cobalt hydroxide, and then the obtained cobalt hydroxide is mixed with a lithium compound. And then calcining the lithium cobaltate. 3. A cobalt hydroxide is obtained by reacting a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity in an aqueous medium, and then sintering the obtained cobalt hydroxide to obtain tetroxide. A method for producing lithium cobalt oxide, comprising obtaining tricobalt, mixing the obtained tricobalt tetroxide with a lithium compound, and firing the mixture. 4. The method according to claim 2, wherein a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity are added to the aqueous medium at the same time and reacted to obtain cobalt hydroxide. The method for producing lithium cobaltate according to the above. 5. An aqueous medium containing a divalent cobalt compound, wherein alkali hydroxide and an ammonium compound exhibiting alkalinity are simultaneously added and reacted to obtain cobalt hydroxide. Or the method for producing lithium cobaltate described in 3. 6. A cobalt hydroxide is obtained by simultaneously adding and reacting a divalent cobalt compound and an alkali hydroxide into an aqueous medium containing an ammonium compound exhibiting alkalinity. Or the method for producing lithium cobaltate described in 3. 7. A reaction product is obtained by adding a divalent cobalt compound, an alkali hydroxide and an ammonium compound exhibiting alkalinity to an aqueous medium, and then reacting the obtained reaction product with an alkali hydroxide. The method for producing lithium cobaltate according to claim 2 or 3, wherein cobalt hydroxide is obtained. 8. A method for producing a cobalt hydroxide by reacting a divalent cobalt compound with an ammonium compound exhibiting alkalinity in an aqueous medium, and then reacting the obtained reaction product with an alkali hydroxide. The method for producing lithium cobaltate according to claim 2 or 3, wherein: 9. A positive electrode for a lithium battery, comprising the lithium cobaltate according to claim 1. 10. A lithium battery comprising the positive electrode according to claim 9.