JPH05343066A - Positive electrode active material for lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide a positive electrode active material for a lithium secondary battery by which corrosion of a positive electrode current collecting body can be prevented by regulating the total content of sodium and potassium in not more than a specific quantity in composite oxide composed of lithium and transition metal of a specific ratio. CONSTITUTION:For example, lithium carbonate and so on and a single body of transition metal or the carbonate and oxide thereof are mixed together, and a heat treatment is carried out, and composite oxide shown by LixMO2 (x represents 0.3-1.2 and M represents transition metal) is prepared. At this time, cleaning of a raw material is repeated in pure water, or ethylene diamine tetraacetate is added to raw material aqueous solution, and the total content of sodium and potassium associated in the composite oxide is set not more than 1000ppm, or preferably, it is set not more than 200ppm. Thereby, a positive electorde active material to prevent effectively corrosion of a positive electrode current collecting body of a lithium secondary battery can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium secondary battery, and particularly to a lithium secondary metal composite oxide which can effectively prevent corrosion of a positive electrode current collector of the secondary battery. The present invention relates to a positive electrode active material for batteries.

[0002]

2. Description of the Related Art Hitherto, as a positive electrode active material for a lithium secondary battery, materials such as sulfide-based materials such as titanium disulfide and molybdenum disulfide have been proposed, and some of these have already been put to practical use. Has been done. However, when these sulfide-based positive electrode active materials are used, since the battery voltage is 3.0 V or less, there is a problem that the battery voltage is low from the viewpoint of obtaining a battery with high energy density.

Therefore, in order to obtain a lithium secondary battery having a high energy density, a cobalt lithium composite oxide (L
It has been studied to use a composite oxide of lithium and a transition metal such as iCoO ₂ ) as a positive electrode active material, and some of these have already been put to practical use.

By the way, when a composite oxide of lithium and a transition metal is used as the positive electrode active material described above, an aluminum foil or the like is proposed as a positive electrode current collector (Japanese Patent Laid-Open No. 1-294372). reference),
It is being put to practical use.

However, when the above-mentioned composite oxide with a transition metal is used as the positive electrode active material, there is a problem that the aluminum current collector is often corroded and the battery characteristics are deteriorated. Therefore, corrosion does not occur in the positive electrode active material. In order to obtain the substance, there was no choice but to devise a special and complicated firing method, etc., but still a stable positive electrode active material could not be obtained.

As described above, the production of the positive electrode active material is not simply required to have excellent battery performance, and the importance of compatibility with other battery constituent materials is that the battery cans of Ikeda et al. Corrosion (electrochemistry 45 (5), 316 (197)
It is also clear in the report of 7)).

[0007]

SUMMARY OF THE INVENTION In view of the circumstances described above, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery which can prevent corrosion of the positive electrode current collector.

[0008]

Means for Solving the Problems As a result of intensive studies on the corrosion of an aluminum current collector, the inventors of the present invention have found that corrosion is promoted when the content of sodium and potassium in the positive electrode active material is large. I found it. Therefore, the above object of the present invention is achieved by controlling the contents of sodium and potassium contained in the positive electrode active material.

That is, the positive electrode active material for a lithium secondary battery of the present invention comprises lithium and a transition metal represented by Li _x MO ₂ (1) (x: 0.3 to 1.2, M is a transition metal). The total content of sodium and potassium in the composite oxide is 1000 ppm or less.

The present invention will be described in more detail below. In the present invention, a composite oxide of lithium and a transition metal represented by Li _x MO ₂ (1) (x: 0.3 to 1.2, M is a transition metal) is a lithium carbonate or a transition metal. Mixing simple substance or its carbonate, oxide,
It is easily synthesized by heat treatment (for example, Mat, Res. Bull by Mizushima, etc.,
15, 783 (1980)).

In the above formula, x is in the range of 0.30 to 1.2. This range is a composite oxide of LiMO ₂ and Li _0.5.
This is because the deviation from the stoichiometric composition when synthesizing MO ₂ is taken into consideration.

The transition metal (M) used here is not particularly limited, but examples thereof include cobalt, nickel and manganese.

In the present invention, the total content of sodium and potassium as associated components in the composite oxide is 1
It should be 000 ppm or less, preferably 500
ppm or less, more preferably 200 ppm or less.

When the amount of these accompanying components exceeds 1000 ppm, the pH rises, the aluminum foil as the positive electrode current collector is corroded, and the battery characteristics are deteriorated. Furthermore, when the amount of these accompanying components exceeds 3000 ppm, p
The increase in H becomes remarkable, and the degree of corrosion of the aluminum foil becomes remarkable.

Thus, the total content of sodium and potassium as an accompanying component in the complex oxide is 1000 p.
The pm or less can be achieved by reducing the contents of sodium and potassium in the raw materials for production. Specifically, the manufacturing raw material is repeatedly washed in pure water, and ethylenediaminetetraacetic acid (ED
TA) and the like.

As described above, the present invention uses the lithium-transition metal composite oxide in which the total content of sodium and potassium in the positive electrode active material of the lithium secondary battery is suppressed to 1000 ppm or less. Corrosion can be suppressed and its industrial value is extremely large.

[0017]

EXAMPLES The present invention will be described in detail below based on examples and comparative examples.

Example 1 The content of sodium and potassium was reduced by the method shown below for each of cobalt trioxide and lithium carbonate which are raw materials for producing lithium cobalt oxide.

That is, for cobalt trioxide,
100 g of the sample was placed in a beaker containing 1 liter of pure water, heated to 70 ° C., stirred with a stir bar for 2 hours, and then filtered. This operation was repeated 3 times, and the sodium content was 1200
0ppm to 40ppm, and potassium content 50ppm
To 10 ppm respectively.

For lithium carbonate, lithium oxide
1 liter of a solution of 45 g / l monohydrate was prepared, 2 g of EDTA was added to remove sodium and potassium, the mixture was heated to 90 ° C., 80 g of ammonium carbonate was added, and the mixture was heated and stirred for 30 minutes. 11 filtered and collected
Obtained by drying at 0 ° C. for 2 hours. By this method, the sodium content was reduced from 120 ppm to 20 ppm, and the potassium content was reduced from 10 ppm to 1 ppm.

The cobalt trioxide thus obtained and lithium carbonate were added so that the cobalt / lithium ratio was 1.05, and they were sufficiently mixed, and then in air (nitrogen / oxygen = 80/20: volume). Ratio) and heated at 900 ° C. for 5 hours to cause a reaction to obtain a lithium cobalt composite oxide (LiCoO ₂ ).

The contents of sodium and potassium in this lithium cobalt composite oxide were measured by atomic absorption spectrometry, and the results are shown in Table 1.

Also, 10 g of this lithium-cobalt composite oxide was taken, and about 5 was put in a beaker containing 20 cc of pure water.
After stirring for 3 minutes with a stirrer, a commercial aluminum plate (thickness: 0.3 mm) cut into a 3 cm square was applied in a slurry form and left for 48 hours to evaluate the degree of corrosion of the aluminum plate. The results are shown in Table 1. Here, “large” means corrosion of more than 1/2 of the entire surface, and “medium” means 1 of the entire surface.
Corrosion of / 4 to 1/2, and "small" indicates corrosion of less than 1/4 of the entire surface.

Examples 2 to 9 Lithium-cobalt composite oxides were obtained in the same manner as in Example 1 except that a certain amount of sodium carbonate or potassium carbonate was added when mixing cobalt tetraoxide and lithium carbonate.

With respect to these lithium-cobalt composite oxides, the sodium and potassium contents were measured in the same manner as in Example 1, and the degree of corrosion of the aluminum plate was evaluated. The results are shown in Table 1.

Comparative Examples 1-2 Lithium-cobalt composite oxides were all prepared in the same manner as in Example 1 except that the sodium and potassium contents were not reduced by using commercially available cobalt trioxide and lithium carbonate. Got

With respect to these lithium-cobalt composite oxides, the sodium and potassium contents were measured in the same manner as in Example 1, and the degree of corrosion of the aluminum plate was evaluated. The results are shown in Table 1.

[0028]

[Table 1]

As shown in Table 1, in Examples 1 to 9 in which the total content of sodium and potassium is 1000 ppm or less, the lithium-cobalt composite oxides have a total content of sodium and potassium of more than 1000 ppm. Compared with Comparative Examples 1 and 2 using the cobalt composite oxide, the aluminum plate is less corroded. In particular, the effect is remarkable in Examples 1 to 3 and 6 to 7.

[0030]

As described above, according to the present invention,
Since the total content of sodium and potassium in the lithium-transition metal composite oxide is suppressed to 1000 ppm or less, the corrosion prevention of the positive electrode current collector of the lithium secondary battery can be dramatically improved, and as a result, This has the effect of improving the characteristics of the secondary battery.

Claims (2)

[Claims] 1. A total content of sodium and potassium in a composite oxide of lithium and a transition metal represented by Li _x MO ₂ (1) (x: 0.3 to 1.2, M is a transition metal). A positive electrode active material for a lithium secondary battery, which is 1000 ppm or less. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the total content of sodium and potassium is 200 ppm or less.