JPH11233113A - Manufacture of li-co complex oxide for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relatively easily increase the amount of baking by adding carbon dioxide gas into the atmosphere during cooling of a baked product and setting the concentration of the carbon dioxide gas in the atmosphere at a specific value. SOLUTION: A mixture of a lithium compound and a cobalt compound is baked using, e.g. a pusher type continuous tunnel furnace having a variable feed rate adjusting function. T o cool the baked product obtained, carbon dioxide gas is added into the atmosphere. Therefore during cooling the baked product, lithium oxide remaining in the baked product can be rapidly and readily changed into lithium carbonate. As a result, Li-Co complex oxides achieving the theoretical residual amount of lithium carbonate can be obtained. The concentration of the carbon dioxide gas in the atmosphere during cooling is set at 0.5 to 3.0 vol.%. Thus, since almost all of excess lithium can be converted into lithium carbonate, safety can be ensured and productivity is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Li-Co for a secondary battery particularly suitable for a positive electrode active material of a lithium ion secondary battery.
The present invention relates to a method for producing a composite oxide.

[0002]

2. Description of the Related Art Hitherto, as a positive electrode active material of a lithium ion secondary battery, a Li—Co-based composite oxide has been widely used.

[0003] Such a Li-Co-based composite oxide is prepared by mixing a lithium compound (for example, lithium carbonate) powder and a cobalt compound (for example, cobalt tetroxide) powder and keeping them at about 980 ° C for several hours in air. And then gradually cooled to about 200 ° C. in air.

When a lithium compound and a cobalt compound are mixed, lithium is stoichiometrically about 10% excess of cobalt (eg, Li _1.11 CoO ₂ ).
It is mixed so that it becomes. The reason is as follows.

[0005] That is, most of the excessive lithium content exists in the form of lithium oxide immediately after firing, but during cooling after firing, it reacts with carbon dioxide gas in the air to change to lithium carbonate. When a lithium ion secondary battery is assembled using such a Li-Co-based composite oxide containing lithium carbonate, when an abnormal battery reaction occurs, lithium carbonate is decomposed to generate carbon dioxide gas, and as a result , The internal pressure of the battery can increases.
Therefore, the battery safety device can be operated smoothly.

When Li _1.11 CoO ₂ is produced using lithium carbonate and cobalt tetroxide, the _two are theoretically reacted in amounts shown in the following reaction formula.

[0007]

(3Li ₂ CO ₃ ) 1.11 + 2Co ₃ O ₄ → 6LiCoO ₂ + (3Li ₂ CO ₃ ) 0.11 3 × 73.88 × 1.11 2 × 240.79 6 × 97.84 3 × 73.88 × 0.11 = 587.04 = 24.38 The theoretical remaining amount of lithium is

[0008]

## EQU1 ## As shown in the formula, theoretical residual amount of lithium carbonate = (3Li ₂ CO ₃ ) 0.11 / (6LiCoO ₂ + (3Li ₂ CO ₃ ) 0.11) = 24.38 / (587.04 + 24.38) = 0.03987, 3.987% Becomes

[0009]

However, not all of the excess lithium is converted to lithium carbonate, and part of the lithium remains as lithium oxide. There is a problem that the numerical value falls below 3.0 to 3.5%. In addition, there is a problem that the remaining amount of lithium oxide varies due to a difference in the structure of the firing furnace used or a difference in the firing lot. For this reason, when preparing a positive electrode mixture paint, lithium oxide is used as a binder (PVDF).
As a result, the viscosity of the coating material increased, and the viscosity was varied, resulting in unstable coating conditions.

Further, in order to increase the production amount of the Li—Co-based composite oxide, the amount of the mixture of the lithium compound powder and the cobalt compound powder to be charged into the sintering furnace is increased and the speed of charging and unloading the mixture into the sintering furnace is increased. It has been attempted to change the firing conditions such as. However, such a change in the firing conditions changes the cooling speed of the fired product after firing,
As a result, there is a problem that the residual amount of lithium oxide increases. Therefore, it has been difficult to increase the amount of sintering treatment per one sintering furnace.

After calcination, the Li—Co-based composite oxide (eg, LiCoO ₂ ) is left in air for a long time, and the remaining lithium oxide therein is reacted with CO ₂ in air to form lithium carbonate. Attempts have been made to change them, but there have been problems such as an increase in lead time and adsorption of moisture.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to quickly and easily remove an excessive lithium content when producing a Li—Co-based composite oxide for a secondary battery. It is an object of the present invention to make it possible to convert the amount of calcination treatment relatively easily into lithium carbonate.

[0013]

Means for Solving the Problems The present inventors calcined a mixture of a lithium compound powder and a cobalt compound powder, and introduced carbon dioxide gas into a cooling atmosphere when cooling the calcined product. The present inventors have found that the lithium component present in the compound can be quickly and easily converted to lithium carbonate, and have completed the present invention.

That is, the present invention relates to a method for producing a Li—Co-based composite oxide for a secondary battery by mixing a lithium compound and a cobalt compound, firing and cooling the obtained fired product. Provided is a production method characterized in that carbon dioxide is added to an atmosphere in cooling an object.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, Li- for a secondary battery according to the present invention will be described.
The method for producing the Co-based composite oxide will be described in detail.

In the method for producing a Li—Co-based composite oxide for a secondary battery according to the present invention, first, a lithium compound and a cobalt compound are mixed.

As the lithium compound, lithium carbonate,
Lithium oxide and the like can be given. Examples of the cobalt compound include cobalt tetroxide, cobalt carbonate and the like. These are preferably mixed in a powder state.

Further, in addition to the lithium compound and the cobalt compound, other metal element compounds (for example, aluminum oxide, nickel oxide, vanadium pentoxide, etc.) may be mixed.

The mixing ratio of the lithium compound and the cobalt compound is such that the lithium compound is in a stoichiometric excess with respect to the cobalt compound. For example, a compound in a stoichiometrically balanced state is LiCoO ₂ or LiCoO ₂
In the case of Co _0.96 Al _0.04 O ₂ , Li _1.11
Compounds represented by CoO ₂ or Li _1.11 Co _0.96 Al _0.04 O ₂ can be mentioned.

Next, the mixture of the lithium compound and the cobalt compound is fired by a known method. For example, firing can be performed using a pusher-type continuous tunnel furnace having a variable feed rate adjusting function. FIG. 1 (schematic sectional view) and FIG. 2 show a general pusher type continuous tunnel furnace.
This will be described with reference to (a) (schematic view in the longitudinal direction).

In this tunnel furnace, as shown in FIG. 1, a bed C which is movable by a conveyor in a space surrounded by a heat-resistant wall W (space in the tunnel furnace) is provided.
On the platform C, a heat-resistant boat B for storing a fired product is placed. Further, the tunnel furnace has a heater h for heating the inside of the tunnel furnace, a gas supply port G for supplying gas to the space inside the tunnel furnace, and a gas detection hole S for measuring the concentration of the atmosphere gas in the furnace. And a damper D for adjusting the gas concentration in the furnace.

In such a tunnel furnace, first, as shown in FIG. 2A, for example, a start zone F at an entrance and heating zones H1 to H1 at which temperatures can be set are arranged in a longitudinal direction.
5, followed by cooling zones C1 and C2 for cooling the fired material, and a final zone Z at an outlet where the fired material can be further water-cooled. Particularly in the final zone Z, the fired product is
It is set so that the furnace can be discharged at a temperature of 00 ° C or less.

In each zone, gas supply ports G1
To G17, the gas detection holes S1 to S17, and the damper D1
To D13. The gas concentration in each zone can be adjusted by the amount of gas supplied from each gas supply port and the amount of gas exhausted from each damper. The firing temperature conditions can be set by adjusting the heating temperature of each heating zone and the feed rate of the object to be fired.

The heat-resistant boat B can be reused by a return conveyor system.

FIG. 2B shows a general relation diagram between each zone in the longitudinal direction of the tunnel furnace and the internal temperature. As can be seen from this figure, the firing of the Li—Co-based composite oxide
This is performed by gradually raising the temperature of the object to be fired to around 980 ° C. and maintaining the temperature for a certain time (for example, 2 to 5 hours). The atmosphere during firing may be an air atmosphere, and it is not necessary to introduce a special gas other than air from the outside to the inside of the firing furnace.

After firing, in the present invention, the obtained fired product is cooled, and carbon dioxide is added to the atmosphere at that time. As a result, during cooling of the fired product, the lithium oxide remaining in the fired product can be quickly and easily changed to lithium carbonate, and as a result, the Li—Co-based composite that has achieved the theoretical remaining amount of lithium carbonate An oxide can be obtained.

When the concentration of carbon dioxide in the atmosphere at the time of cooling is preferably too low, the conversion of lithium oxide to lithium carbonate is not sufficient, and when it is too high, it is wasteful. Set to 0% by volume.

The Li—Co-based composite oxide thus obtained can be preferably used as a positive electrode active material of a lithium ion secondary battery.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

EXAMPLE 1 To prepare Li _1.11 Co _0.96 Al _0.04 O ₂ , 1.11 mol of lithium carbonate and 0.6 mol of cobalt tetroxide were mixed with 1.11 mol of lithium carbonate.
Mixture of 4 mol and 0.04 mol of alumina (substance to be fired)
4.5 Kg is put into a high-purity alumina heat-resistant boat,
Firing and cooling were performed in a pusher-type continuous tunnel furnace shown in FIGS. 1 and 2A so that the furnace temperature and the carbon dioxide concentration in the furnace as shown in FIG. 3 were obtained. Thereby, Li-C
An o-based composite oxide (Li _1.11 Co _0.96 Al _0.04 O ₂ ) was obtained.

In FIG. 3, the carbon dioxide gas concentration is increased when the temperature is raised, because the carbonic acid residue of lithium carbonate is decomposed when the temperature of the material to be fired is raised. When the temperature of the material to be fired was about 900 ° C., most of the carbonic acid residues had been decomposed, so that a decrease in carbon dioxide gas concentration was observed. In this embodiment, at the time of starting the cooling, the carbon dioxide gas was introduced into the furnace until the carbon dioxide gas concentration became about 4%, and thereafter, a carbon dioxide gas concentration curve as shown in FIG. 3 was obtained. That is, the carbon dioxide concentration was adjusted according to the temperature range as shown in Table 1.

[0032]

[Table 1] Temperature range CO2 concentration 950-900 ° C: 3.0% or more 900-700 ° C: 2.0% or more 700-400 ° C: 1.0% or more 400-200 ° C: 0.5% or more

Example 2 The feed rate of the object to be fired was 1.5 times that of Example 1, the heating zone was expanded, the firing temperature was set to 980 ° C. for 3.0 hours, and the carbon dioxide in the cooling zone was set. Except that the gas concentration was adjusted as shown in FIG. 4, a Li—Co-based composite oxide (Li _1.11 Co _0.96 Al
_0.04 O ₂ ).

Example 3 A heat-resistant boat made of high-purity alumina was placed on a spacer (25 m
except that the double stack through m) are similar to Example 1 (with reference FIG. 3) Li-Co-based composite oxide (Li _1.11
Co _0.96 Al _0.04 O ₂ ) was obtained.

Comparative Example 1 As shown in FIG. 5, the firing temperature was 980 ° C.
A Li—Co-based composite oxide (Li _1.11 Co _0.96 Al _0.04 O ₂ ) was obtained in the same manner as in Example 1 except that the temperature was maintained for 0 hour and Air was flowed through the cooling zone. At this time, the carbon dioxide concentration in the cooling zone at 950 ° C. or less was 2.0% or less.

(Evaluation) Li of Examples 1-3 and Comparative Example 1
The residual lithium carbonate content of the -Co-based composite oxide was measured.
Table 2 shows the results.

The theoretical amount of lithium carbonate remaining in this composite oxide was 4.03 as shown in the following equation.
7%.

[0038]

## EQU2 ## Theoretical residual amount of lithium carbonate = 3 (Li ₂ CO ₃ )
0.11 / (6LiCo _0.96 Al _0.04 O ₂ +
_{(3Li 2 CO 3) 0.11)} = 0.04037

[0039]

[Table 2] Residual lithium carbonate% Residual rate% Residual lithium carbonate (converted) Example 1 4.03 99.83 Li ₂ CO ₃ 0.1098 Example 2 4.01 99.33 Li ₂ CO ₃ 0.1093 Example 3 / Lower 3.98 98 .59 Li ₂ CO ₃ 0.1084 / Upper 4.02 99.58 Li ₂ CO ₃ 0.1095 Comparative Example 1 3.60 89.12 Li ₂ CO ₃ 0.0980

As is evident from Table 2, most of the excess lithium was present as lithium carbonate in the Li-Co-based composite oxides of Examples 1 to 3.

On the other hand, in the case of the Li—Co-based composite oxide of Comparative Example 1, it was found that about 10% of excess lithium remained as lithium oxide.

From the above results, it is possible to convert almost all of the excess lithium into lithium carbonate by setting the concentration of carbon dioxide in the atmosphere at the time of cooling the fired product to 0.5 to 3.0%. Was completed. As a result, safety required for the secondary battery can be ensured, and moreover, stable supply of characteristic materials can be achieved, and productivity can be improved.

[0043]

According to the present invention, Li-Co for a secondary battery is provided.
In producing a system-based composite oxide, an excessive amount of lithium can be quickly and easily converted to lithium carbonate, so that it is relatively easy to increase the amount of calcination treatment.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a firing furnace used in the present invention.

FIG. 2 is a schematic diagram of the longitudinal direction of the firing furnace used in the present invention (FIG. (A)), and a diagram showing the relationship between each zone in the longitudinal direction of the firing furnace and the internal temperature (FIG. (B)). .

FIG. 3 is an explanatory view of firing conditions in Examples 1 and 3.

FIG. 4 is an explanatory view of firing conditions in Example 2.

FIG. 5 is an explanatory view of firing conditions of Comparative Example 1.

[Explanation of symbols]

W heat-resistant wall, C baseboard, B heat-resistant boat, h heater,
G gas supply port, S gas detection hole, D damper

Claims (4)

[Claims] 1. A method for producing a Li-Co-based composite oxide for a secondary battery by mixing a lithium compound and a cobalt compound, firing and cooling the obtained fired product, wherein the fired product is cooled. A production method characterized by adding carbon dioxide gas to the atmosphere at the time. 2. The method according to claim 1, wherein the concentration of carbon dioxide in the atmosphere at the time of cooling is set to 0.5 to 3.0% by volume. 3. The method according to claim 1, wherein lithium carbonate is used as the lithium compound, and cobalt tetroxide is used as the cobalt compound. 4. The method according to claim 1, wherein the lithium compound is used in a stoichiometric excess relative to the cobalt compound.