Method for preparing precursor of lithium composite transition metal oxide using a reactor

Abstract

Disclosed is a method for preparing a precursor of lithium composite transition metal oxide for lithium secondary batteries, using a reactor having a closed structure including an outer stationary cylinder; an inner rotary cylinder on the same axis; and a rotation reaction area disposed between them, wherein ring-shaped vortex pairs that are uniformly arranged in a rotation axis direction and rotate in opposite directions are formed in the rotation reaction area. According to the method of the invention, raw materials comprising an aqueous solution of two or more transition metal salts, an aqueous solution of a complex forming additive, and a basic aqueous solution for maintaining pH are fed through an inlet into the rotation reaction area where a coprecipitation reaction is performed under a non-nitrogen atmosphere to form lithium composite transition metal oxide particles which are then discharged through a reactor outlet.

Claims

1. A method for preparing composite transition metal hydroxide particles using a reactor having a closed structure, the method comprising: injecting raw materials comprising an aqueous solution of two or more transition metal salts, an aqueous solution of a complex-forming additive, and a basic aqueous solution for maintaining pH of an aqueous solution of the raw materials within a range of 10 to 12, into a rotation reaction area of a reactor through an inlet; and performing a coprecipitation reaction under a non-nitrogen atmosphere for 1 to 6 hours, wherein the reactor comprises: a stationary hollow cylinder; a rotary cylinder having the same axis as the stationary hollow cylinder and an outer diameter smaller than an inner diameter of the stationary hollow cylinder; an electric motor to generate power, enabling rotation of the rotary cylinder; a rotation reaction area disposed between the stationary hollow cylinder and the rotary cylinder, wherein ring-shaped vortex pairs that are uniformly arranged in a rotation axis direction and rotate in opposite directions are formed in the rotation reaction area; and an inlet through which a reactant fluid is fed into the rotation reaction area and an outlet through which the reactant fluid is discharged from the rotation reaction area, wherein there is a distance between the stationary hollow cylinder and the rotary cylinder, and the ratio of that distance to the outer radius of the rotary cylinder is between 0.05 and 0.4.

2. The method according to claim 1, wherein a kinematic viscosity of reactant fluid is 0.4 to 400 cP and power consumed per unit weight thereof is 0.05 to 100 W/kg.

3. The method according to claim 1, wherein a critical Reynolds number of the vortex pairs is 300 or more.

4. The method according to claim 1, wherein the inlet comprises two or more inlets.

5. The method according to claim 4, wherein the two or more inlets are arrayed in a line by a predetermined distance in a direction of the outlet.

6. The method according to claim 1, wherein the aqueous solution of a complex-forming additive is present in an amount of 0.01 to 10% by weight, based on the total amount of the two or more transition metal salts.

7. The method according to claim 6, wherein the aqueous solution of a complex-forming additive is an aqueous ammonia solution.

8. The method according to claim 1, wherein the transition metal salt is a transition metal sulfate and/or a transition metal nitrate.

9. The method according to claim 8, wherein the sulfate comprises one or two or more selected from the group consisting of nickel sulfate, cobalt sulfate and manganese sulfate, and the nitrate comprises one or two or more selected from the group consisting of nickel nitrate, cobalt nitrate and manganese nitrate.

10. The method according to claim 1, wherein the transition metal composite hydroxide is a compound represented by Formula 1 below:
M(OH.sub.1?x).sub.2(1) wherein M comprises two or more selected from the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr and transition metals of the second period of the Periodic Table of the Elements; and 0?x?0.8.

11. The method according to claim 10, wherein M comprises two or more transition metals selected from the group consisting of Ni, Co and Mn.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic side view illustrating a reactor according to one embodiment of the present invention;

(2) FIG. 2 is a schematic view illustrating flow behaviors of ring-shaped vortex pairs and reactant fluids generated in rotation reaction area of the reactor of FIG. 1;

(3) FIG. 3 is a schematic side view illustrating a reactor according to another embodiment of the present invention;

(4) FIG. 4 is a graph showing comparison in power consumed per unit weight between a CSTR and a reactor according to the present invention;

(5) FIG. 5 is a graph showing a particle size distribution of precursor particles (mean particle diameter (D50): 4.07 ?m) of Example 1;

(6) FIGS. 6A and 6B are SEM images of Example 1 and Comparative Example 1, as specific examples of the present invention; and

(7) FIG. 7 is a graph showing electrochemical properties of lithium secondary batteries prepared in accordance with the method according to one embodiment of the present invention.

BEST MODE

(8) Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only to illustrate the present invention and should not be construed as limiting the scope and spirit of the present invention.

(9) FIG. 1 is a schematic side view illustrating a reactor according to one embodiment of the present invention, FIG. 2 is a schematic view illustrating flow behaviors of ring-shaped vortex pairs and reactant fluids generated in rotation reaction area of the reactor of FIG. 1, and FIG. 3 is a schematic side view illustrating a reactor according to another embodiment of the present invention.

(10) Referring to FIG. 1, a reactor 100 for preparing a precursor of lithium composite transition metal oxide for lithium secondary batteries according to the present invention include a rotary cylinder 120 mounted in the stationary hollow cylinder 110, wherein the rotary cylinder 120 has the same rotation axis as the stationary hollow cylinder 110 and has an outer diameter (2?r2) smaller than an inner diameter (2?r1) of the stationary hollow cylinder, rotation reaction area is formed between the stationary hollow cylinder 110 and the rotary cylinder 120, a plurality of inlets 140, 141 and 142, through which reactant fluids are injected into the rotation reaction area, and an outlet 150, through which reactant fluids are discharged from the rotation reaction area, are formed on the stationary hollow cylinder 110, and an electric motor 130 to generate power, enabling rotation of the rotary cylinder 120, is provided at a side of the stationary hollow cylinder 110.

(11) A ratio (d/r2) of the distance (d) between the stationary hollow cylinder 110 and the rotary cylinder 120 to the outer radius (r2) of the rotary cylinder 120 determines an effective volume of the rotation reaction area.

(12) Referring to FIGS. 1 and 2, when the rotary cylinder 120 is rotated by the power generated from the electric motor 130 and an Reynolds number reaches a critical level, reactant fluids such as aqueous solution of composite transition metal hydroxide, aqueous ammonia solution and an aqueous sodium hydroxide solution injected into the rotation reaction area through the inlets 140, 141 and 142 receive centrifugal force in the direction of the stationary hollow cylinder 110 from the rotary cylinder 120 and thus become unstable. As a result, ring-shaped vortex pairs 160 rotating in opposite directions along the rotation axis direction are uniformly arrayed.

(13) The length of the ring-shaped vortex pairs 160 in a direction of gravity is substantially equivalent to the distance (d) between the stationary hollow cylinder 110 and the rotary cylinder 120.

(14) In order to prevent permeation of air into the gap between a rotation axis and a bear ring during rotation of the rotary cylinder 120, the rotation axis may be sealed using a sealing material such as O-ring.

(15) Referring to FIGS. 1 and 3, reactant materials such as aqueous transition metal salt solution, aqueous ammonia solution and aqueous sodium hydroxide solution may be injected through the inlet 140 into the rotation reaction area and different kinds of materials such as coating materials may be injected through the inlet 141 or the inlet 142 into the rotation reaction area.

(16) As shown in FIG. 3, a reactor according to another embodiment of the present invention includes storage tanks 180 and 181 to store reactant fluids such as an aqueous transition metal salt solution, an aqueous ammonia solution and an aqueous sodium hydroxide solution, and a metering pump 170 to control an amount of reactant fluids injected into the rotation reaction area.

(17) The aqueous transition metal salt solution may be injected into rotation reaction area using the metering pump 170, while taking into consideration retention time, the aqueous sodium hydroxide solution may be variably injected into the rotation reaction area using the metering pump 170 such that pH is maintained at a predetermined level, and the aqueous ammonia solution may be continuously supplied through the metering pump 170.

(18) After completion of reaction, the composite transition metal hydroxide is obtained through the outlet 150.

(19) The reactor 100 may further include a heat exchanger mounted on the stationary hollow cylinder 110, to control a reaction temperature in the process of mixing reactant fluids using vortex pairs 160 in the rotation reaction area between the stationary hollow cylinder 110 and the rotary cylinder 120, and the heat exchanger may be selected from heat exchangers well-known in the art to which the present invention pertains.

(20) FIG. 4 is a graph showing comparison in power consumed per unit weight between a CSTR and a reactor according to the present invention. A 4 L CSTR consumes a rotation power of 1,200 to 1,500 rpm to obtain a desired particle size in precursor synthesis. This power is about 13 to 27 W/kg, when converted into a rotation power per unit weight (region A). Meanwhile, the 0.5 L reactor according to the present invention enables synthesis of precursors having a desired particle size in a rotation power range of 600 to 1,400 rpm. This power is about 1 to 8 W/kg, when converted into a rotation power per unit weight (region B).

(21) That is, the reactor of the present invention enables synthesis of precursors having desired particle size using at a lower stirring power per unit weight, as compared to CSTR. This means that the reactor of the present invention has superior stirring efficiency as compared to CSTR.

EXAMPLE 1

(22) Nickel sulfate, cobalt sulfate and manganese sulfate were mixed at a ratio (molar ratio) of 0.50:0.20:0.30, a 1.5M aqueous transition metal solution was prepared and a 3M aqueous sodium hydroxide solution was then prepared. As the ammonia solution, an aqueous solution in which ammonium ions are dissolved at 25 wt % was prepared.

(23) The prepared aqueous transition metal solution was injected into the reactor using the metering pump for a retention time of one hour. The aqueous sodium hydroxide solution was variably injected using a metering pump such that pH is maintained at 11.0. The aqueous ammonia solution was continuously supplied at a concentration of 30 mol %, based on the aqueous transition metal solution.

(24) The mean retention time was one hour, the reaction was continued for 20 hours after reached in a normal state, and the resulting nickel-cobalt-manganese composite transition metal precursor was washed with distilled water several times, and dried in a 120? C. constant-temperature drier for 24 hours, to prepare a nickel-cobalt-manganese composite transition metal precursor.

EXAMPLE 2

(25) A nickel-cobalt-manganese composite transition metal precursor was prepared in the same manner as in Example 1, except that supply amounts were changed so as to adjust the retention time to 2 hours.

EXAMPLE 3

(26) A nickel-cobalt-manganese composite transition metal precursor was prepared in the same manner as in Example 1, except that supply amounts were changed so as to adjust the retention time to 3 hours.

EXAMPLE 4

(27) A nickel-cobalt-manganese composite transition metal precursor was prepared in the same manner as in Example 1, except that supply amounts were changed so as to adjust the retention time to 6 hours.

COMPARATIVE EXAMPLE 1

(28) A nickel-cobalt-manganese composite transition metal precursor was prepared in the same manner as in Example 4, except that a continuous stirred tank reactor (CSTR) was used and an aqueous ammonia solution was added at a concentration 50 mol % of the aqueous transition metal solution.

EXPERIMENTAL EXAMPLE 1

Comparison in Production Amount Per Reactor Volume According to Retention Time

(29) Production amounts according to volumes of the reactors used in Examples 1 to 4 and Comparative Example 1 were compared and the results thus obtained are shown in Table 1 below.

(30) TABLE-US-00001 TABLE 1 Retention Production amount per time reactor volume (g/L-hr) Ex. 1 1 hour 55.4 Ex. 2 2 hours 27.7 Ex. 3 3 hours 18.5 Ex. 4 6 hours 9.2 Comp. Ex. 1 6 hours 6.1

EXPERIMENTAL EXAMPLE 2

Analysis of Impurity Content

(31) 0.01 g of the prepared transition metal precursor was accurately metered and added to a 50 mL corning tube, and a small amount of acid was added dropwise thereto, followed by mixing while shaking. When the mixed sample was completely dissolved and was transparent in color, a concentration of SO.sub.4 in the sample was measured using an Ion Chromatograph (DX500, model produced by Dionex Corp.). The results thus obtained are shown in Table 2 below.

(32) TABLE-US-00002 TABLE 2 Retention time SO.sub.4 concentration (wt %) Ex. 1 1 hour 0.40 Ex. 2 2 hours 0.38 Ex. 3 3 hours 0.34 Ex. 4 6 hours 0.30 Comp. Ex. 1 6 hours 0.45

EXPERIMENTAL EXAMPLE 3

Particle Size Distribution Graph

(33) FIG. 5 is a graph showing a particle size distribution of precursor particles (mean particle diameter (D50): 4.07 ?m) of Example 1, and FIGS. 6A and 6B are SEM images of Example 1 and Comparative Example 1, as specific examples of the present invention.

(34) The following Table 3 shows mean particle sizes (D50) and coefficient of variation of precursor particles of Example 1 and Comparative Example 1. It can be seen from Table 3 that the precursor particles of Example 1 had a mean particle diameter of 5 ?m or less, and coefficient of variation thereof had a single distribution of 0.375. On the other hand, the precursor particles of Comparative Example 1 had a mean particle diameter larger than 8 ?m, and coefficient of variation thereof was 0.706. The precursor particles of Comparative Example 1 exhibited bad single distribution, as compared to precursor particles of Example 1.

(35) TABLE-US-00003 TABLE 3 Mean particle size (D50) C.V. Ex. 1 4.07 ?m 0.375 Comp. Ex. 1 9.46 ?m 0.706

EXPERIMENTAL EXAMPLE 4

Production of Coin Cells and Evaluation of Electrochemical Properties

(36) The prepared transition metal precursors and Li.sub.2CO.sub.3 were mixed at a ratio (weight ratio) of 1:1, heated at an elevation speed of 5? C./min and baked at 920? C. for 10 hours to prepare a lithium composite transition metal oxide powder (cathode active material). The cathode active material powder thus prepared was mixed with Denka as a conductive agent and KF 1100 as a binder at a weight ratio of 95:2.5:2.5 to prepare a slurry, and the slurry was uniformly coated on an Al foil with a thickness of 20 ?m. The coated material was dried at 130? C. to produce a cathode for lithium secondary batteries.

(37) 2032 coin cells were produced using the cathode for lithium secondary batteries thus produced, a lithium metal foil as a counter electrode (anode), a polyethylene membrane (Celgard, thickness: 20 ?m) as a separation membrane, and a liquid electrolyte in which 1M LiPF.sub.6 was dissolved in a mixed solvent containing ethylene carbonate, dimethylene carbonate and diethyl carbonate at a ratio of 1:2:1.

(38) For the coin cells, electric properties of cathode active material were evaluated using an electrochemical analyzer (Toyo System, Toscat 3100U) at 3.0 to 4.25V. The results thus obtained are shown in Table 4.

(39) TABLE-US-00004 TABLE 4 Initial discharge capacity Initial efficiency 2C/0.1C (mAh/g) (%) (%) Ex. 1 168.3 89.8 88.5 Ex. 2 167.3 89.1 87.9 Ex. 3 166.9 89.4 87.8 Ex. 4 166.8 89.6 87.0 Comp. Ex. 1 165.2 87.6 85.2

(40) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, 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 as disclosed in the accompanying claims.