Precursor particles of lithium composite transition metal oxide for lithium secondary battery and cathode active material comprising the same

Abstract

Disclosed are precursor particles of a lithium composite transition metal oxide for lithium secondary batteries, wherein the precursor particles of a lithium composite transition metal oxide are composite transition metal hydroxide particles including at least two transition metals and having an average diameter of 1 m to 8 m, wherein the composite transition metal hydroxide particles exhibit monodisperse particle size distribution and have a coefficient of variation of 0.2 to 0.7, and a cathode active material including the same.

Claims

1. Precursor particles of a lithium composite transition metal oxide for lithium secondary batteries, wherein the precursor particles are composite transition metal hydroxide particles comprising at least two transition metals and having an average diameter of 1 m to 8 m, wherein the composite transition metal hydroxide particles exhibit monodisperse particle size distribution and have a coefficient of variation of 0.2 to 0.7, wherein the composite transition metal hydroxide particles contain an impurity derived from a transition metal salt for preparation of a composite transition metal hydroxide, wherein an amount of the impurity is 0.3 wt % to 0.4 wt % based on of total weight of the composite transition metal hydroxide particles, wherein the impurity is a salt ion comprising a sulfate ion (SO.sub.4.sup.2), and wherein the composite transition metal hydroxide is a compound represented by Formula 1 below:
M(OH.sub.1-x).sub.2(1), wherein M includes two or more transition metals selected from the group consisting of nickel, cobalt and manganese; and 0x0.8.

2. The precursor particles according to claim 1, wherein the average diameter of the composite transition metal hydroxide particles is 1 m to 5 m.

3. The precursor particles according to claim 1, wherein the amount of the impurity is 0.3 wt % to 0.4 wt % based on the total weight of the composite transition metal hydroxide particles.

4. The precursor particles according to claim 1, wherein the transition metal salt is a sulfate.

5. The precursor particles according to claim 4, wherein the sulfate is at least one selected from the group consisting of nickel sulfate, cobalt sulfate, and manganese sulfate.

6. The precursor particles according to claim 1, wherein the salt ion further comprises a nitrate ion (NO.sub.3.sup.).

7. The precursor particles according to claim 1, wherein M further includes at least one additional transition metal selected from the group consisting of aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B), chromium (Cr), and period 2 transition metals.

8. The precursor particles according to claim 1, wherein M includes each of nickel, cobalt and manganses, and optionally further includes at least one additional transition metal selected from the group consisting of aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B), chromium (Cr), and period 2 transition metals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIGS. 1A and 1B are scanning electron microscope (SEM) images of transition metal precursors prepared according to Example 1 and Comparative Example 1;

(3) FIG. 2 is a graph showing particle size distribution of transition metal precursor particles (D50: 4.07 m) of Example 1;

(4) FIG. 3 is a graph showing electrochemical characteristics of lithium secondary batteries each including transition metal precursor particles prepared using a preparation method according to an embodiment of the present invention;

(5) FIG. 4 is a side view of a reactor according to an embodiment of the present invention;

(6) FIG. 5 is a view illustrating ring-shaped vortex pairs generated in a rotating reaction space of the reactor of FIG. 4 and a flow shape of a reaction fluid;

(7) FIG. 6 is a view of a reactor according to another embodiment of the present invention; and

(8) FIG. 7 is a graph showing comparison in power consumption per unit mass between a CSTR and the reactor according to the present invention.

MODE FOR INVENTION

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

Example 1

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

(11) The aqueous transition metal solution was continuously pumped into the reactor using a metering pump so that residence time thereof was 1 hour. The aqueous sodium hydroxide solution was pumped in a rate-variable manner using a metering pump so that pH thereof was maintained at 11.0. The aqueous ammonia was continuously supplied in an amount of 30 mol % based on the amount of the aqueous transition metal solution.

(12) In this regard, average residence time was 1 hour. After reaching the steady state, a nickel-cobalt-manganese composite transition metal precursor, which was prepared by 20-hour continuous reaction, was washed several times with distilled water and dried in a 120 C. constant-temperature drying oven for 24 hours to obtain a final nickel-cobalt-manganese composite transition metal precursor.

Example 2

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

Example 3

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

Example 4

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

Comparative Example 1

(16) 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 the aqueous ammonia was supplied in an amount of 50 mol % based on the amount of the aqueous transition metal solution.

Experimental Example 1

Comparison in Productivity Per Unit Reactor Volume According to Residence Time

(17) Productivities per unit volume of the reactors used in Examples 1 to 4 and Comparative Example 1 were compared. Results are shown in Table 1 below.

(18) TABLE-US-00001 TABLE 1 Productivity per volume of Residence time reactor (g/L-hr) Example 1 1 hour 55.4 Example 2 2 hours 27.7 Example 3 3 hours 18.5 Example 4 6 hours 9.2 Comparative Example 1 6 hours 6.1

Experimental Example 2

Analysis of Amount of Impurities

(19) 0.01 g of each of the prepared transition metal precursors was accurately weighed and added to a 50 mL Corning tube, a small amount of acid was added dropwise thereto, and the resulting material was mixed by shaking. When the mixed sample was fully dissolved, the concentration of SO.sub.4.sup.2 of each sample was measured using an ion chromatograph (DX500 manufactured by Dionex). Results are shown in Table 2 below.

(20) TABLE-US-00002 TABLE 2 Concentration Residence time of SO.sub.4.sup.2 (wt %) Example 1 1 hour 0.40 Example 2 2 hours 0.38 Example 3 3 hours 0.34 Example 4 6 hours 0.30 Comparative Example 1 6 hours 0.45

Experimental Example 3

Particle Size Distribution Graph

(21) FIGS. 1A and 1B are scanning electron microscope (SEM) images of the transition metal precursors of Example 1 and Comparative Example 1. FIG. 2 is a graph showing particle size distribution of precursor particles (mass median diameter (D50): 4.07 m) of Example 1.

(22) Table 3 shows D50 and coefficient of variation of each of the precursor particles of Example 1 and the precursor particles of Comparative Example 1. Referring to Table 3, it can be confirmed that the precursor particles of Example 1 have an average diameter of 5 m or less and a coefficient of variation of 0.375 (monodispersion), while the precursor particles of Comparative Example 1 have an average diameter of greater than 8 m and a coefficient of variation of 0.706, which indicates poorer monodispersion than the precursor particles of Example 1.

(23) TABLE-US-00003 TABLE 3 Mass median diameter (D50) C.V. Example 1 4.07 m 0.375 Comparative Example 1 9.46 m 0.706

Experimental Example 4

Manufacture of Coin Cell and Evaluation of Electrochemical Characteristics Thereof

(24) Each of the prepared transition metal precursors and Li.sub.2CO.sub.3 were mixed in a weight ratio of 1:1 and the resultant mixture was calcined at 920 C. for 10 hours at a heating rate of 5 C./min to prepare a powder-type lithium transition metal oxide as a cathode active material. Subsequently, the powder-type cathode active material, Denka as a conductive material, and KF 1100 as a binder were mixed in a weight ratio of 95:2.5:2.5 to prepare a slurry and the slurry was uniformly coated on 20 m thick Al foil. Thereafter, the coated Al foil was dried at 130 C., thereby completing manufacture of a cathode for lithium secondary batteries.

(25) The fabricated cathode, a lithium metal foil as a counter electrode (an anode), and a polyethylene film as a separator (Celgard, thickness: 20 m), and a liquid electrolyte containing 1M LiPF.sub.6 dissolved in a mixed solvent of ethylene carbonate, dimethylene carbonate, and diethyl carbonate in a volume ratio of 1:2:1 were used to manufacture a 2032 coin cell.

(26) Electrical properties of the cathode active material of each coin cell were evaluated at 3.0 to 4.25 V using an electrochemical analyzer (Toscat 3100U available from Toyo Systems). Results are shown in Table 4 below.

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

(28) FIG. 4 is a side view of a reactor 100 according to an embodiment of the present invention. FIG. 5 is a view illustrating ring-shaped vortex pairs generated in a rotating reaction space of the reactor of FIG. 4 and a flow shape of a reaction fluid.

(29) FIG. 6 is a view of a reactor 100 according to another embodiment of the present invention.

(30) Referring to FIG. 4, the reactor 100 for preparation of a precursor of a lithium composite transition metal oxide for lithium secondary batteries includes a hollow fixed cylinder 110 installed horizontally with respect to the ground, a rotating cylinder 120 disposed in the hollow fixed cylinder 110, having the same rotating shaft as that of the fixed cylinder 110, and having an outer diameter (2r2) smaller than an inner diameter (2r1) of the fixed cylinder 110, a rotating reaction space formed between the fixed cylinder 110 and the rotating cylinder 120, a plurality of inlets 140, 141 and 142 through which a reaction fluid is introduced into the rotating reaction space and an outlet 150 to discharge the reaction fluid, wherein the inlets 140, 141 and 142 and the outlet 150 are disposed on the fixed cylinder 110, and an electric motor 130 provided at a side surface of the fixed cylinder 110 to generate power for rotation of the rotating cylinder 120.

(31) An effective volume of the rotating reaction space is determined by a ratio (d/r2) of a distance d between the fixed cylinder 110 and the rotating cylinder 120 to an outer radius r2 of the rotating cylinder 120.

(32) Referring to FIGS. 4 and 5, when the rotating cylinder 120 is rotated by power generated by the electric motor 130 and thus reaches a critical Reynolds number, reaction fluids such as an aqueous solution of a composite transition metal hydroxide, aqueous ammonia, an aqueous sodium hydroxide solution, and the like introduced into the rotating reaction space via the inlets 140, 141 and 142 become unstable by centrifugal force applied towards the fixed cylinder 110 from the rotating cylinder 120 and, as a result, ring-shaped vortex pairs 160 rotating in opposite directions along a rotating shaft are periodically arranged in the rotating reaction space.

(33) The length of the ring-shaped vortex pairs 160 in the direction of gravity is almost the same as the distance d between the fixed cylinder 110 and the rotating cylinder 120.

(34) The outside of the rotating shaft may be sealed by a sealing member such as an O-ring to prevent air from being sucked into a gap between the rotating shaft and a bearing when the rotating cylinder 120 is rotated.

(35) Referring to FIGS. 4 and 6, an aqueous transition metal salt solution, aqueous ammonia, an aqueous sodium hydroxide solution, and the like may be introduced into the rotating reaction space via the inlet 140 and heterogeneous materials such as a coating material may be introduced into the rotating reaction space via the inlet 141 or 142.

(36) Referring to FIG. 6, the reactor 100 according to another embodiment of the present invention further includes storage tanks 180 and 181 to store an aqueous transition metal salt solution, aqueous ammonia, an aqueous sodium hydroxide solution, and the like and a metering pump 170 to control the amounts of reaction fluids introduced into the rotating reaction space.

(37) The aqueous transition metal salt solution may be introduced into the rotating reaction space using the metering pump 170 in consideration of residence time, the aqueous sodium hydroxide solution may be introduced into the rotating reaction space in a rate-variable manner using the metering pump 170 so that pH thereof was kept constant, and the aqueous ammonia may be continuously supplied using the metering pump 170.

(38) After reaction was completed, the prepared composite transition metal hydroxide was obtained via the outlet 150.

(39) To adjust reaction temperature in a process of mixing the reaction fluids in the rotating reaction space between the fixed cylinder 110 and the rotating cylinder 120 using the vortex pairs 160, the reactor 100 may further include a heat exchanger on the fixed cylinder 110. The heat exchanger may be any heat exchanger that is commonly known in the art to which the present invention pertains.

(40) FIG. 7 is a graph showing comparison in power consumption per unit mass between a CSTR and the reactor according to the present invention. A 4 L CSTR operates at a rotational speed of 1200 to 1500 rpm to form a desired particle size when synthesizing a precursor and, when the rotational speed is converted into stirring power per unit mass, the corresponding value is about 13 to 27 W/kg (see region A of FIG. 7). By contrast, a 0.5 L reactor according to the present invention enables synthesis of a precursor with a desired particle size at a rotational speed of 600 rpm to 1400 rpm and, when the rotational speed is converted into stiffing power per unit mass, the corresponding value is 1 W/kg to 8 W/kg (see region B of FIG. 7).

(41) That is, the reactor according to the present invention enables synthesis of a precursor with a desired particle size using less stirring power per unit mass than the CSTR. This indicates that the reactor has higher stirring efficiency than that of the CSTR.

(42) 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.

INDUSTRIAL APPLICABILITY

(43) As described above, composite transition metal hydroxide particles according to the present invention have a small average diameter, exhibit monodisperse particle size distribution, and are uniform and thus exhibit excellent rate characteristics, excellent low-temperature rate characteristics, and excellent electrode density.

(44) In addition, the composite transition metal hydroxide particles have high crystallinity and thus have increased reactivity with a lithium precursor and, accordingly, a calcination temperature of a lithium composite transition metal oxide may be reduced.