JP3267667B2 - Method for producing positive electrode for lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode for a lithium secondary battery, which can maintain a constant particle size distribution of a positive electrode active material without adding a pulverizing step.

[0002]

2. Description of the Related Art A lithium secondary battery comprises a positive electrode, a lithium negative electrode, a separator and a non-aqueous electrolyte interposed between the positive and negative electrodes, and these are housed in a case.

As a positive electrode active material, LiCoO ₂ , LiNi
When a lithium metal composite oxide such as O ₂ is used, 4
A high voltage of V or more can be obtained, which is suitable for improving the performance of a battery. As the metal used for the composite oxide, there is one or several kinds of metals or alloy powders selected from Co, Ni, Fe, and Mn. These metals have conventionally been used as starting materials in the form of carbonates such as lithium carbonate and nickel carbonate, oxides such as CoO and NiO, or hydroxides such as Co (OH) ₂ , which are highly reactive during synthesis to obtain fine particles. Heat treatment together with the lithium salt provided a positive electrode active material.

[0004]

However, Co,
When carbonates, oxides, and hydroxides of Ni and Fe are used as starting materials, the reactivity is high, and the crystals grow during the heat treatment to produce coarse particles.
In this pulverizing step, it is difficult to control the particle size distribution, and there has been a problem of deterioration of characteristics which is considered to be caused by contamination of impurities in the pulverizing process.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to eliminate a pulverization step and to easily obtain a powder of a positive electrode active material having a desired particle size distribution. An object of the present invention is to provide a method for manufacturing a battery positive electrode.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method of using lithium metal or an alloy thereof or a lithium occlusion material for a negative electrode, and using Co,
In a lithium secondary battery using a composite oxide of one or several kinds of metals selected from Ni and Fe and lithium, the Co, Ni, Fe used as a starting material of a positive electrode active material is used.
Is composed of a metal or alloy powder, the average particle size of these raw material powders is adjusted to 0.2 to 9 μm, and this is heated together with a lithium compound to produce a lithium metal composite oxide. is there.

Further, Li ₂ C is used as the lithium compound.
This compound can be mixed with the metal or its alloy powder using O ₃ or LiOH, and can be subjected to heat treatment after being deposited in a container by natural fall.

[0008]

By using a metal or alloy powder having a particle size of 0.2 to 9 μm as a starting material, the particle size of a product constituting the positive electrode active material composed of a lithium metal composite oxide after the heat treatment has a particle size of the raw material powder. The particle size is almost the same, and the pulverizing step can be omitted in controlling the particle size.

[0009] Such an effect is presumed to be due to the reaction proceeding when lithium and oxygen enter the metal particles, mainly in the metal or alloy particles.

[0010]

Next, an embodiment of the present invention will be described. However, the present invention is not limited to the following examples.

Embodiment 1 FIG. The average particle diameters of about 0.1 μm, 0.2 μm, 0.5 μm,
1 μm, 5 μm, and 10 μm Co powder and Li ₂ CO ₃ were adjusted and mixed at a molar ratio of Co: Li of 1: 1 and deposited in a container by gravity falling.
Heat treatment was performed for 2 hours. Although the obtained product composed of the lithium-cobalt composite oxide was secondary-agglomerated, it was collapsed into a powdery state by lightly pressing. As a result of measuring the average particle diameter of each of the above products, as shown in Table 1, it was confirmed that there was a correlation between the average particle diameter of the starting material and the average particle diameter of the product.

[0012]

[Table 1] As shown in Table 1, the raw material powder has a particle size of 0.2 to 1
The product using 0 μm Co powder had the same particle size of the product, and the average particle size was almost the same as that of the raw material powder. Also, only when the raw material powder was 0.1 μm, the average particle size of the product was large, and the shape and size of the particles were also varied. This means that the average particle size of the raw material powder is 0.1 μm
If so, it is presumed that the reactivity was increased as in the case where commercially available cobalt carbonate was used as a starting material, and crystal growth occurred.

Comparative Example 1 Commercially available cobalt carbonate and Li ₂ C
O ₃ was mixed at a molar ratio of Co: Li of 1: 1 and heated in air at 800 ° C. for 12 hours. The obtained product had an average particle size of 17 μm, and the particle size was widely distributed as 2 to 30 μm. This product was designated as sample symbol G. Separately, the product was pulverized with a ball mill to obtain products having an average particle size of 3 μm (sample symbol H) and 1 μm (sample symbol I).

Next, the first embodiment will be described. And Comparative Example 1.
A positive electrode was made using each of the samples A to I obtained in the above, and a coin type 2016 battery was prototyped, and its capacity characteristics in the cycle at the time of charging and discharging were examined. The result shown in FIG. 1 was obtained. . The positive electrode was mixed at a ratio of active material (each sample): graphite: PTFE = 8: 1: 1,
It was prepared as a 0.1 g pellet. Metal lithium was used as a counter electrode, and PC / 1 mol LiClO ₄ was used as an electrolyte.

The charge / discharge voltage employed in the test was 4.2 V-
3.5 V and this was repeated 30 times. The capacity ratio (unit:%) in the figure is a relative value when the first cycle of sample B is 100.

As apparent from FIG. 1, samples B to E
When the particle size of Co is 0.2 to 5 μm, the particle size of the product is stable, and since the particle size is small, the discharge capacity after 30 cycles is large.

Further, it is presumed that the sample F having a particle diameter of 10 μm has a large particle diameter and has poor characteristics due to diffusion resistance.
Some of the samples A and G have a large particle size, and it is presumed that the characteristics are inferior. Further, sample H,
In the case of the pulverized material like I, the cycle characteristics are inferior even if the first cycle is equivalent to the present invention. It is also presumed that this is because the layer structure of the particles was destroyed by the pulverization or impurities were mixed.

Embodiment 2 FIG. Atomization method and pulverization of the Ni—
Co alloy powder (Ni: Co = 1: 1) and Li ₂ CO ₃ were adjusted to a molar ratio of Ni: Co: Li of 1: 1: 2, mixed, and deposited in a container by gravity falling. Thereafter, heat treatment was performed at 700 ° C. for 24 hours in an oxygen atmosphere.

Comparative Example 2 Commercially available nickel carbonate, cobalt carbonate and Li ₂ CO ₃ were adjusted at a molar ratio of Ni: Co: Li of 1: 1: 2 and mixed, and heat treatment was performed under the same conditions as in Example 2.

As a result of measuring the average particle size of each of the above products, as shown in Table 2, it was confirmed that there was a correlation between the average particle size of the starting material and the average particle size of the product.

[0021]

[Table 2] In addition, Comparative Example 2. Although the average particle size of the raw material powder was 0.1 μm, the product sample grew crystal and became larger in particle size than the starting material.
A sample N of μm was used.

Next, the second embodiment will be described. And Comparative Example 2.
Using each of the samples J to N obtained in the above, a positive electrode was made under the same conditions as in Example 1, and a coin-type 2016 battery was prototyped, and the capacity characteristics in the cycle at the time of charging and discharging were examined. The result shown in FIG. 2 was obtained.

The capacity ratio (unit:%) in the figure is the sample J
Is a relative value when the first cycle of is set to 100.

As apparent from FIG. 2, samples J and K
When the particle size of the Ni—Co alloy is 0.2 to 9 μm, the particle size of the product is stable and the particle size is small, so that the discharge capacity after 30 cycles is large.

Samples L and M are presumed to have inferior characteristics due to large particle size and diffusion resistance. Further, the pulverized product such as sample N is inferior in cycle characteristics even if the first cycle is equivalent to the present invention. This is presumed to be because the layer structure of the particles was destroyed by the pulverization as described above, or impurities were mixed.

Embodiment 3 FIG. , Comparative Example 3. Average particle size of about 0.2 μm, 5 μm, 10
μm Fe—Co alloy powder (Fe: Co = 1: 1) and L
i ₂ CO _{3 at} a molar ratio of Ni: Co: Li of 1: 1:
Then, the mixture was adjusted to 2, mixed, and deposited in a container by natural fall, and then heat-treated at 700 ° C. for 24 hours in an oxygen atmosphere.

Comparative Example 3 In this case, an oxide is used and Fe
₂ O ₃ , Co ₃ O ₄ and Li ₂ CO ₃ are converted to Fe: C
The mixture was adjusted at a molar ratio of o: Li of 1: 1: 2, and heat-treated under the same conditions as in Example 2.

As a result of measuring the average particle size of each of the above products, as shown in Table 3, it was confirmed that there was a correlation between the average particle size of the starting material and the average particle size of the product.

[0029]

[Table 3] Comparative Example 3. Although the average particle size of the raw material powder was 1 μm, it was confirmed that the product sample grew to a crystal size of 15 μm and was larger in particle size than the starting material.

In each of the above embodiments, Li ₂ CO ₃ was used as the lithium source of the lithium metal composite oxide.
The same effect by using the OH is Ru obtained.

[0031]

As described in detail in the above examples, according to the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, a metal or alloy powder having a particle size of 0.2 to 9 μm is used as a starting material. As a result, the particle size of the product constituting the positive electrode active material composed of the lithium metal composite oxide after the heat treatment becomes substantially the same as the particle size of the raw material powder, and a pulverizing step is performed in controlling the particle size of the positive electrode active material. Can be omitted. In addition, since the destruction of the layer structure of the particles and the incorporation of impurities can thereby be prevented, the discharge capacity can be improved and the cycle characteristics can be improved.

In addition, as shown in the examples, the method of performing heat treatment after depositing in a container by natural dropping after mixing makes the production easier than before.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. , Comparative Example 1. 3 is a graph showing capacity characteristics in a cycle at the time of charging and discharging of FIG.

FIG. , Comparative Example 2. 3 is a graph showing capacity characteristics in a cycle at the time of charging and discharging of FIG.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hayato Komatsubara 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Inventor Hidenori Nakura 5-36-11 Shimbashi, Minato-ku, Tokyo (56) References JP-A-1-289066 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 C01G 25/00-47 / 00 C01G 49/10-57/00

Claims (2)

(57) [Claims] 1. A negative electrode comprising metallic lithium or an alloy thereof or a lithium absorbing material, and Co, Co,
In a lithium secondary battery using a composite oxide of one or more kinds of metals selected from Ni and Fe and lithium, the Co, Ni, Fe, which is a starting material of a positive electrode active material, is made of gold. A lithium metal composite oxide by subjecting these raw material powders to an average particle size of 0.2 to 9 μm and subjecting them to heat treatment together with a lithium compound. Method for producing positive electrode for secondary battery. 2. The method according to claim 1, wherein the lithium compound is Li ₂ CO _3.
2. The positive electrode for a lithium secondary battery according to claim 1, wherein the compound is mixed with the metal or its alloy powder using LiOH, and heat-treated after being deposited in a container by natural fall. 3. Manufacturing method.