MANUFACTURING METHOD OF CATHODE ACTIVE MATERIAL FOR SECONDARY CELL

Abstract

The present invention relates to a method of preparing a positive electrode active material precursor for secondary batteries which allows maintenance of the crystallinity of an obtained positive electrode active material precursor at a high level while allowing control of a particle diameter of the positive electrode active material precursor. More particularly, the method of preparing a positive electrode active material precursor for secondary batteries includes (1) a preparation step of preparing a continuous-type reactor that includes a non-rotatable cylinder, inside which a reaction chamber is included; a stirring motor disposed at one side of the non-rotatable cylinder; a stirring rod that is coupled with a motor shaft of the stirring motor and is embedded inside the reaction chamber while being spaced from a wall of the reaction chamber; and a pH sensor for measuring pH inside the reaction chamber; (2) a gap adjustment step of adjusting a gap that is an interval between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder to be proportional to an average particle diameter of a positive electrode active material precursor to be obtained; and (3) a reaction step of supplying a metal solution and an alkaline solution for precipitation of the metal solution, to constitute the positive electrode active material precursor to be obtained, into the reaction chamber while rotating the stirring rod of the gap-adjusted continuous-type reactor, and allowing reaction for 30 minutes to 24 hours while maintaining pH inside the reaction chamber at 10.5 to 12.8.

Claims

1. A method of preparing a positive electrode active material precursor for secondary batteries, the method comprising: (1) a preparation step of preparing a continuous-type reactor that comprises a non-rotatable cylinder, inside which a reaction chamber is comprised; a stirring motor disposed at one side of the non-rotatable cylinder; a stirring rod that is coupled with a motor shaft of the stirring motor and is embedded inside the reaction chamber while being spaced from a wall of the reaction chamber; and a pH sensor for measuring pH inside the reaction chamber; (2) a gap adjustment step of adjusting a gap that is an interval between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder to be proportional to an average particle diameter of a positive electrode active material precursor to be obtained; and (3) a reaction step of supplying a metal solution and an alkaline solution for precipitation of the metal solution, to constitute the positive electrode active material precursor to be obtained, into the reaction chamber while rotating the stirring rod of the gap-adjusted continuous-type reactor, and allowing reaction for 30 minutes to 24 hours while maintaining pH inside the reaction chamber at 10.5 to 12.8.

2. The method according to claim 1, wherein a solvent of the metal solution and the alkaline solution is an aqueous solvent.

3. The method according to claim 2, wherein a solvent of the metal solution and the alkaline solution is water.

4. The method according to claim 1, wherein the metal solution is an aqueous metal salt solution selected from the group consisting of nickel (Ni), manganese (Mn), cobalt (Co), aluminum (Al), and a mixture of two or more thereof.

5. The method according to claim 1, wherein the alkaline solution is an aqueous sodium hydroxide solution, aqueous ammonia, or a mixture thereof.

6. The method according to claim 1, wherein a rotation speed of the stirring rod is 10 to 3000 rpm.

Description

DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a sectional view schematically illustrating an embodiment of a continuous-type reactor suitable for preparation of a positive electrode active material precursor for secondary batteries according to the present invention.

[0019] FIGS. 2 to 5 illustrate scanning electron microscope images of positive electrode active material precursors for secondary batteries obtained varying gaps according to Examples 1 to 4 of the present invention.

[0020] FIG. 6 illustrates a scanning electron microscope image of a positive electrode active material precursor for secondary batteries obtained according to Comparative Example 1, provided for comparison with the examples of the present invention.

[0021] FIG. 7 illustrates a scanning electron microscope image of a positive electrode active material precursor for secondary batteries obtained according to Comparative Example 2, provided for comparison with the examples of the present invention.

[0022] FIGS. 8 and 9 illustrate scanning electron microscope images of positive electrode active material precursors for secondary batteries obtained, varying reaction time, according to Example 5 of the present invention (FIG. 8) and a graph of a particle size analysis result thereof (FIG. 9).

[0023] FIGS. 10 and 11 illustrate scanning electron microscope images of positive electrode active material precursors for secondary batteries obtained, varying a rotation speed of a stirring rod, according to Example 6 of the present invention (FIG. 10) and a graph of a particle size analysis result thereof (FIG. 11).

[0024] FIGS. 12 and 13 illustrate scanning electron microscope images of positive electrode active material precursors for secondary batteries obtained, varying a supply speed of aqueous ammonia, according to Example 7 of the present invention (FIG. 12) and a graph of a particle size analysis result thereof (FIG. 13).

[0025] FIGS. 14 and 15 illustrate scanning electron microscope images of positive electrode active material precursors for secondary batteries obtained, varying pH, according to Example 8 of the present invention (FIG. 14) and a graph of a particle size analysis result thereof (FIG. 15).

BEST MODE

[0026] Hereinafter, embodiments of the present invention are described in detail with reference to the accompanying drawings.

[0027] A method of preparing a positive electrode active material precursor for secondary batteries according to the present invention includes (1) a preparation step of preparing a continuous-type reactor that includes a non-rotatable cylinder, inside which a reaction chamber is included; a stirring motor disposed at one side of the non-rotatable cylinder; a stirring rod that is coupled with a motor shaft of the stirring motor and is embedded inside the reaction chamber while being spaced from a wall of the reaction chamber; and a pH sensor for measuring pH inside the reaction chamber; (2) a gap adjustment step of adjusting a gap that is an interval between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder to be proportional to an average particle diameter of a positive electrode active material precursor to be obtained; and (3)a reaction step of supplying a metal solution and an alkaline solution for precipitation of the metal solution, to constitute the positive electrode active material precursor to be obtained, into the reaction chamber while rotating the stirring rod of the gap-adjusted continuous-type reactor, and allowing reaction for 30 minutes to 24 hours while maintaining pH inside the reaction chamber at 10.5 to 12.8.

[0028] The preparation step is a preparation step of preparing a continuous-type reactor suitable for production of the positive electrode active material precursor for secondary batteries according to the present invention. Here, a continuous-type reactor 1 may be a continuous-type reactor including a non-rotatable cylinder 11, inside which a reaction chamber 12 is included; a stirring motor 21 disposed at one side of the non-rotatable cylinder 11; a stirring rod 31 that is coupled with a motor shaft 22 of the stirring motor 21 and is embedded inside the reaction chamber 12 while being spaced from a wall of the reaction chamber 12; and a pH sensor 41 for measuring pH inside the reaction chamber, as illustrated in FIG. 1. In particular, the continuous-type reactor 1 may include a plurality of the stirring rod 31 having different diameters suitable for adjustment of an interval between an outer surface of the stirring rod 31 and an inner surface of the non-rotatable cylinder 11, i.e., a gap, in a gap control step described below. To accomplish this, the stirring rod 31 is preferably, detachably coupled with the non-rotatable cylinder 11. However, the present invention is not intended to be limited thereto, and it should be understood that the interval between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder may be adjusted by controlling an inner diameter of the non-rotatable cylinder or adjusting an inner diameter of the non-rotatable cylinder and an outer diameter of the stirring rod together.

[0029] The gap adjustment step may be carried out by adjusting an interval, i.e., a gap, between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder to be proportional to an average particle diameter of a positive electrode active material precursor to be obtained. As described above, an interval, i.e., a gap, between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder may be adjusted by controlling an inner diameter of the non-rotatable cylinder, an outer diameter of the stirring rod, or the inner diameter of the non-rotatable cylinder and the outer diameter of the stirring rod together. The gap adjustment may serve as a key parameter in the method of preparing a positive electrode active material precursor for secondary batteries according to the present invention, particularly as a main parameter for control of a particle diameter of a positive electrode active material precursor to be obtained.

[0030] There action step is carried out by supplying a metal solution and an alkaline solution for precipitation of the metal solution, to constitute the positive electrode active material precursor to be obtained, into the reaction chamber while rotating the stirring rod of the gap-adjusted continuous-type reactor, and allowing reaction for 30 minutes to 24 hours while maintaining pH inside the reaction chamber at 10.5 to 12.8, as described above. In particular, a spherical positive electrode active material precursor crystal may be obtained by adjusting the interval, i.e., a gap, between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder within a range of 1 to 30 mm. When the gap is less than 1 mm, a particle size of an obtained positive electrode active material precursor is too small and agitation force excessively increases, thereby negatively affecting driving of the continuous-type reactor. On the other hand, when the gap is greater than 30 mm, agitation force is excessively decreased, whereby a particle diameter of an obtained positive electrode active material precursor excessively increases or coagulation is not satisfactorily performed. Accordingly, sphericity and crystallinity are decreased, whereby it may be difficult to prepare a positive electrode active material.

[0031] A solvent of the metal solution and the alkaline solution may be an aqueous solvent, preferably water. Selection of a suitable solvent is important in preparing the metal solution and the alkaline solution. In particular, the viscosity of a solvent or the like may be a main parameter greatly affecting Taylor vortex formation in a continuous-type reactor.

[0032] The metal solution may be an aqueous metal salt solution selected from the group consisting of nickel (Ni), manganese (Mn), cobalt (Co), aluminum (Al), and a mixture of two or more thereof. By selecting a suitable one from among these metal solutions and combinations thereof, various positive electrode active materials may be prepared. That is, to prepare a ternary positive electrode active material, for example, a combination of nickel-manganese-cobalt, a combination of nickel-cobalt-aluminum, or the like may be used. Meanwhile, to prepare a quaternary positive electrode active material, for example, a combination of nickel-manganese-cobalt-aluminum may be used. It should be understood that other metals and combinations thereof, other than these exemplary combinations, may be used.

[0033] The alkaline solution may be an aqueous sodium hydroxide solution, aqueous ammonia, or a mixture thereof. In particular, an aqueous sodium hydroxide solution among alkaline solutions may be supplied, varying a supply amount of the aqueous sodium hydroxide solution such that the pH inside the reaction chamber is maintained within a predetermined range suitable for co-precipitation, into the reaction chamber reaction chamber.

[0034] A rotation speed of the stirring rod may be maintained within a range of 10 to 3000 rpm. When a rotation speed of the stirring rod is greater than 3000 rpm, turbulence may occur and thus Taylor flow may be destroyed or disappear.

[0035] Hereinafter, preferred examples and comparative examples of the present invention are described.

[0036] The following examples are provided for illustrative purposes only and should not be construed as limiting the scope and spirit of the present invention.

Example 1

[0037] Preparing a continuous-type reactor that includes a non-rotatable cylinder, inside which a reaction chamber is included; a stirring motor disposed at one side of the non-rotatable cylinder; a stirring rod that is coupled with a motor shaft of the stirring motor and is embedded inside the reaction chamber while being spaced from a wall of the reaction chamber and adjusting a gap that is an interval between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder to 5 mm. Subsequently, to prepare a positive electrode active material precursor, NiSO.sub.4.6H.sub.2O, CoSO.sub.4.7H.sub.2O, and MnSO.sub.4.H.sub.2O were mixed in a molar ratio of 1:1:1 in the reaction chamber while rotating the stirring rod of the gap-adjusted continuous-type reactor, distilled water was added thereto to prepare a 2M solution, and the prepared 2M solution was supplied to the reaction chamber at a rate of 1.98 ml/min. At the same time, a 14% ammonium hydroxide solution was added to the reaction chamber at a rate of 0.2 ml/min and a 4M sodium hydroxide solution was supplied thereto. Here, a supply speed of the 4M sodium hydroxide was set to be controlled so as to maintain the pH of the whole solution in the reaction chamber at pH 11, a rotation speed of the stirring rod was set to 1300 rpm, and a reaction time in the reaction chamber, i.e., a time taken until a solution injected through an injection port was discharged via a discharge part as much as the capacity of the reaction chamber (10 L basis) (time during which one batch stays=reaction time=1), was 4 hours. Accordingly, a positive electrode active material precursor for secondary batteries was obtained. Here, reaction temperature inside the reaction chamber was set to 50 C.

[0038] As a result, an average particle diameter of the positive electrode active material precursor for secondary batteries was 1.9 m, and spherical crystalline particles were observed as illustrated in a scanning electron microscope (SEM) image thereof (FIG. 2).

Example 2

[0039] An experiment was carried out in the same manner as in Example 1, except that the gap was adjusted 9 mm to instead of 5 mm.

[0040] As a result, an average particle diameter of an obtained positive electrode active material precursor for secondary batteries was 4.0 m, and spherical crystalline particles were observed as illustrated in a scanning electron microscope (SEM) image thereof (FIG. 3).

Example 3

[0041] An experiment was carried out in the same manner as in Example 1, except that the gap was adjusted 14 mm to instead of 5 mm.

[0042] As a result, an average particle diameter of an obtained positive electrode active material precursor for secondary batteries was 10.0 m, and spherical crystalline particles were observed as illustrated in a scanning electron microscope (SEM) image thereof (FIG. 4).

Example 4

[0043] An experiment was carried out in the same manner as in Example 1, except that the gap was adjusted 26 mm to instead of 5 mm.

[0044] As a result, an average particle diameter of an obtained positive electrode active material precursor for secondary batteries was 20.0 m, and spherical crystalline particles were observed as illustrated in a scanning electron microscope (SEM) image thereof (FIG. 5).

Comparative Example 1

[0045] An experiment was carried out in the same manner as in Example 1, except that the gap was adjusted 37 mm to instead of 5 mm.

[0046] An obtained positive electrode active material precursor for secondary batteries was not coagulated, whereby it was difficult to measure an average particle diameter thereof. Referring to a scanning electron microscope (SEM) image thereof (FIG. 6), it can be confirmed that coagulation is not satisfactorily performed and crystallinity is not exhibited.

Comparative Example 2

[0047] An experiment was carried out in the same manner as in Example 1, except that the gap was adjusted 1 mm to instead of 5 mm.

[0048] Referring to FIG. 7, it can be confirmed that an obtained positive electrode active material precursor for secondary batteries tends to coagulate, but spherical particles are not satisfactorily formed and the particles tend to be destroyed due to collision among the particles.

Example 5

[0049] An experiment was carried out in the same manner as in Example 1, except that the gap was constantly fixed to 9 mm, a 14% ammonium hydroxide solution was fed into a reaction chamber at a rate of 0.6 ml/min, and a 4M sodium hydroxide solution was supplied thereto. Here, the capacity of the reaction chamber was 1 L and reaction time was set to four hours and seven hours.

[0050] Referring to a scanning electron microscope (SEM) image (FIG. 8) and a graph (FIG. 9), it can be confirmed that a particle diameter of an obtained positive electrode active material precursor for secondary batteries increases proportionally with increasing reaction time.

Example 6

[0051] An experiment was carried out in the same manner as in Example 1, except that the capacity of the reaction chamber was 1 L, the gap was constantly fixed to 9 mm, a 14% ammonium hydroxide solution was supplied to the reaction chamber at a rate of 0.6 ml/min, and a rotation speed (i.e., stirring speed) of the stirring rod was 300 to 1500 rpm. Referring to a scanning electron microscope (SEM) image (FIG. 10) and a graph (FIG. 11), it can be confirmed that a particle diameter of an obtained positive electrode active material precursor for secondary batteries decreases with increasing stirring speed, and, when the stirring speed is lower than a proper rpm range, particle shapes are poor and agglomeration into a spherical shape is not satisfactorily performed.

Example 7

[0052] An experiment was carried out in the same manner as in Example 1, except that the capacity of the reaction chamber was 1 L, the gap was constantly fixed to 9 mm, and a supply speed of a 14% ammonium hydroxide solution into the reaction chamber was changed.

[0053] Referring to a scanning electron microscope (SEM) image (FIG. 12) and a graph (FIG. 13), it can be confirmed that a particle diameter of an obtained positive electrode active material precursor for secondary batteries increases with increasing supply flow rate of the 14% ammonium hydroxide solution.

Example 8

[0054] An experiment was carried out in the same manner as in Example 1, except that the capacity of the reaction chamber was 1 L, the gap was constantly fixed to 9 mm, and the pH of the whole solution in the reaction chamber was differently set to 11 and 11.5 by adjusting a supply speed of a 4M sodium hydroxide solution while varying a supply flow rate of a 14% ammonium hydroxide solution supplied to the reaction chamber.

[0055] Referring to a scanning electron microscope (SEM) image (FIG. 14) and a graph (FIG. 15), it can be confirmed that particle surfaces of an obtained positive electrode active material precursor for secondary batteries became rough and, when the supply flow rate of the ammonium hydroxide solution was greater than 0.6 ml/min, pH greatly affected a particle size thereof. Accordingly, it can be confirmed that there is an appropriate pH range for each supply flow rate of the ammonium hydroxide solution.

[0056] In particular, with regard to the rotation speed of the stirring rod in Examples 1 to 8, an internal volume of the reaction chamber of Examples 1 to 4 was based on 10 L, whereas the internal volume of the reaction chamber of Examples 5 to 8 was based on 1 L. Here, the rotation speed of the stirring rod was experimentally determined. Accordingly, it was confirmed that the rotation speed of the stirring rod might be optimally controlled depending upon the internal volume of the reaction chamber.

[0057] That is, it was confirmed that Taylor No. might be calculated according to Mathematical Equation 1 below, and identical or similar Taylor No. might be formed inside the reaction chamber by utilizing the calculated Taylor No., whereby an identical or similar reaction condition might be set:

[00001]$\begin{array}{cc}{T}_a={\left(\frac{d}{r_i}\right)}^{1/2}.Math.\frac{.Math..Math.r_i.Math.d}{v},& \left[\mathrm{Mathematical}.Math..Math.\mathrm{Equation}.Math..Math.1\right]\end{array}$

wherein Ta represents Taylor No., d represents a distance (m) between an outer surface of a stirring rod and an inner surface of a reaction chamber, ri represents the radius (m) of a stirring rod, represents the angular velocity (rad/s) of a stirring rod, and represents kinematic viscosity (m.sup.2/s).

[0058] Using Mathematical Equation 1, the rotation speed of the stirring rod was calculated to obtain similar Taylor No. (based on Taylor No. of about 15,000) for each volume of the reaction chambers, and results are summarized in Table 1 below. Here, the kinematic viscosity was based on water, and the kinematic viscosity of water was 1.003 at 20 C.:

TABLE-US-00001 TABLE 1 Reactor Rotation speed (rpm) volume Of stirring rod Taylor No. 1 L 1300 14663.43 10 L 204 14697.27 1000 L 8.7 14674.72

[0059] In conclusion, a positive electrode active material precursor for secondary batteries obtained according to the present invention may have relatively high uniformity and sphericity while having various particle diameters due to adjustment of various parameters of the continuous-type reactor, i.e., an interval (i.e., a gap) between an outer surface of the stirring rod and an inner surface of the non-rotatable cylinder, residence time, the rotation speed of the stirring rod, reaction time, and the like, or a combination of two or more thereof.

[0060] The aforementioned description is provided only to illustrate embodiments according to the present invention. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. Therefore, it is obvious that the modifications, additions and substitutions are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS

[0061] 1: CONTINUOUS-TYPE REACTOR [0062] 11: CYLINDER [0063] 12: REACTION CHAMBER [0064] 21: STIRRING MOTOR [0065] 22: MOTOR SHAFT [0066] 31: STIRRING ROD [0067] 41: PH SENSOR