Positive electrode active material for lithium secondary battery and method for preparing the same

Abstract

Provided is a method for preparing a positive electrode active material for a lithium secondary battery, the method comprising: mixing and reacting a nickel source, a cobalt source, and an aluminum source, ammonia water, sucrose, and a pH adjusting agent to prepare a mixed solution; drying and oxidizing the mixed solution to prepare a positive electrode active material precursor; and adding a lithium source to the positive electrode active material precursor and firing them to prepare a positive electrode active material for a lithium secondary battery.

Claims

1. A method for preparing a porous positive electrode active material for a lithium secondary battery, the method comprising: mixing and reacting raw materials including a metal aqueous solution containing a nickel source, a cobalt source, and an aluminum source, ammonia water, sucrose as a pore forming agent, and a pH adjusting agent to prepare a positive electrode active material precursor wherein the sucrose is present in the positive electrode active material precursor; drying and naturally oxidizing the positive electrode active material precursor to prepare a solid positive electrode active material precursor; mixing a lithium salt in a solid form with the solid positive electrode active material precursor to prepare a solid mixture; and firing the solid mixture in air to prepare a positive electrode active material for a lithium secondary battery represented by the following Chemical Formula 1
Li.sub.1+zNi.sub.1−x−yCo.sub.xAl.sub.yO.sub.2  [Chemical Formula 1] (z, x, y, and 1−x−y are real numbers that satisfy the following Equations, respectively: 0≦z≦0.3, 0.05≦x≦0.3, and 0.4≦1−x−y<0.95), wherein a content of the sucrose contained in the metal aqueous solution is 5 to 30 weight %, wherein in firing, the sucrose which is present in the solid positive electrode active material precursor is carbonized and pores are formed in the positive electrode active material, and wherein the positive electrode active material has a total pore volume of 6.5×10.sup.−2 to 8.0×10.sup.−2 cc/g and a specific surface area of 0.7 to 1.0 m.sup.2/g.

2. The method of claim 1, wherein the firing is performed for 15 to 20 hours through a first step of raising a temperature to 400˜500° C. at a rate of 0.5 to 1° C./min; and a second step of raising a temperature to 800˜900° C. at a rate of 1 to 2° C./min.

3. The method of claim 1, wherein a concentration of the metal in the metal aqueous solution is 1 to 3M.

4. The method of claim 3, wherein a molar ratio of nickel, cobalt, and aluminum contained in the metal aqueous solution is 0.5 to 0.94:0.05 to 0.3: 0.01 to 0.3.

5. The method of claim 3, wherein the metal aqueous solution is supplied into a reactor at a rate of 0.2 to 0.5 L/hr.

6. The method of claim 1, wherein pH of the mixture at the time of conducting the mixing reaction is 11 to 13.

7. The method of claim 1, wherein a concentration of the ammonia water is 0.1 to 0.25 times a mole concentration of the metal in the metal aqueous solution.

8. The method of claim 7, wherein the ammonia water is supplied at a rate of 0.02 to 0.05 L/hr.

9. The method of claim 1, wherein the lithium salt is LiOH.

Description

BEST MODE

(1) Hereinafter, the present invention will be described in detail through the Examples. However, these Examples are only to illustrate the present invention, and those skilled in the art will appreciate that these Examples are not to be construed as limiting a scope of the present invention.

EXAMPLE 1

(2) In a 4 L reactor, a metal aqueous solution in which nickel sulfate (NiSO.sub.36H.sub.2O), cobalt sulfate (CoSO.sub.47H.sub.2O), and aluminum sulfate (Al.sub.2(SO.sub.4).sub.318H.sub.2O) were dissolved at a concentration of 2M and 20 weight % of sucrose is contained was supplied at a rate of 0.3 L/hr. In this case, the metal aqueous solution contained nickel sulfate (NiSO.sub.36H.sub.2O), cobalt sulfate (CoSO.sub.47H.sub.2O), and aluminum sulfate (Al.sub.2(SO.sub.4).sub.318H.sub.2O) so that nickel, cobalt, and aluminum had a molar ratio of 0.7:0.1:0.2.

(3) 0.2M ammonia water was supplied into the reactor at a rate of 0.03 L/hr, and sodium hydroxide was added thereto so as to have pH of 11, followed by reaction with stirring the reactor, thereby preparing a mixed solution. At this time, an average temperature was maintained at 40° C. at the time of the reaction.

(4) A rotary blade of the reactor was designed as two reverse rotational rotary blades for vertically uniform mixing, and an output of a rotation motor was 2.4 kw. The number of revolutions was 1500 rpm.

(5) The reactant obtained from the reactor was dried at 110° C. for 15 hours and then naturally oxidized for 12 hours in the air to prepare a positive electrode active material precursor.

(6) After the prepared active material precursor and lithium hydroxide (LiOH) were mixed at a molar ratio of 1:1.05, a temperature was raised to 500° C. at a rate of 1° C./min to perform heat-treatment for 5 hours, and then the temperature was raised again to 900° C. at a rate of 2° C./min to perform the firing so that the total firing time became 20 hours, thereby preparing a positive electrode active material for a lithium secondary battery, Li.sub.1.05Ni.sub.0.7Co.sub.0.1Al.sub.0.2O.sub.2. In the prepared positive electrode active material for a lithium secondary battery, uniform particles having an average diameter of 10 μm and pores formed therein was obtained.

EXAMPLE 2

(7) A positive electrode active material for a lithium secondary battery, Li.sub.1.05Ni.sub.0.6Co.sub.0.1Al.sub.0.3O.sub.2, was prepared by the same method as in Example 1 except that the metal aqueous solution contained nickel sulfate (NiSO.sub.36H.sub.2O), cobalt sulfate (CoSO.sub.47H.sub.2O), and aluminum sulfate (Al.sub.2(SO.sub.4).sub.318H.sub.2O) so that nickel, cobalt, and aluminum had a molar ratio of 0.6:0.1:0.3.

COMPARATIVE EXAMPLE 1

(8) A positive electrode active material for a lithium secondary battery was prepared by the same method as in Example 1 except that sucrose was not contained.

(9) Specific surface areas and average pore volumes of the particles prepared in Example 1 and Comparative Example 1 were measured, and the results were shown in Table 1.

(10) TABLE-US-00001 TABLE 1 Specific surface area (m.sup.2/g) Pore volume (cc/g) Example 1 0.8 7.130 × 10.sup.−2 Comparative 0.6 5.830 × 10.sup.−3 Example 1

(11) As shown in Table 1, it may be appreciated that in the case of the positive electrode active material according to the present invention, the porous particle having a significantly large pore volume was prepared, and the specific surface area was significantly large.

(12) Capacities of the particles prepared in Examples 1 and 2 and Comparative Example 1 were measured, and the results were shown in Table 2.

(13) TABLE-US-00002 TABLE 2 Capacity (mAh/g) Example 1 215 Example 1 205 Comparative Example 1 200