Precursor for preparation of lithium composite transition metal oxide and method of preparing the same

Abstract

Disclosed are a transition metal precursor for preparation of a lithium composite transition metal oxide, the transition metal precursor including a composite transition metal compound represented by Formula 1 below and a hydrocarbon compound, and a method of preparing the same:
Mn.sub.aM.sub.b(OH.sub.1-x).sub.2(1)
wherein M is at least two selected from the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr, and second period transition metals; 0.4a1; 0b0.6; a+b1; and 0x0.5, in which the transition metal precursor includes a particular composite transition metal compound and a hydrocarbon compound, and thus, when a lithium composite transition metal oxide is prepared using the same, carbon may be present in lithium transition metal oxide particles and/or on surfaces thereof, whereby a secondary battery including the lithium composite transition metal oxide exhibits excellent rate characteristics and long lifespan.

Claims

1. A transition metal precursor for preparation of a lithium composite transition metal oxide, the transition metal precursor comprising a composite transition metal compound represented by Formula 1 below and a hydrocarbon compound:
Mn.sub.aM.sub.b(OH.sub.1-x).sub.2(1) wherein M is at least two selected from the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr, Ti and Zr; 0.4a1; 0b0.6; a+b1; and 0<x<0.5, wherein an amount of the hydrocarbon compound is in a range of 0.1 to 10 wt % based on a total amount of the transition metal precursor, wherein the transition metal precursor has closed pores, and at least a portion of the hydrocarbon compound is contained in the closed pores.

2. The transition metal precursor according to claim 1, wherein M is at least one transition metal selected from the group consisting of Ni and Co.

3. The transition metal precursor according to claim 1, wherein 0.5a1.

4. The transition metal precursor according to claim 1, wherein 0.1b0.5.

5. The transition metal precursor according to claim 1, wherein the composite transition metal compound is a composite transition metal compound represented by Formula 2 below:
Mn.sub.aNi.sub.cCo.sub.1-(a+c+d)M.sub.d(OH.sub.1-x).sub.2(2) wherein 0.6a1; 0.1c0.5; 0d0.1; a+c+d1; M is at least one selected from the group consisting of Al, Mg, Cr, Ti, Cu, Fe, and Zr; and x is the same as defined in claim 1.

6. The transition metal precursor according to claim 1, wherein an amount of the composite transition metal compound is 30 wt % or greater based on a total amount of the transition metal precursor.

7. The transition metal precursor according to claim 1, wherein the hydrocarbon compound is a saccharide-based material.

8. The transition metal precursor according to claim 7, wherein the saccharide-based material is at least one selected from the group consisting of fructose, sucrose, glucose, galactose, lactose, maltose, starch, and dextrin.

9. The transition metal precursor according to claim 8, wherein the saccharide-based material is sucrose.

10. The transition metal precursor according to claim 1, wherein the hydrocarbon compound is present in the transition metal precursor and/or on a surface thereof.

11. A method of preparing the transition metal precursor according to claim 1, the method comprising: preparing an aqueous transition metal solution containing a transition metal salt for preparation of the transition metal precursor; mixing a hydrocarbon compound into the aqueous transition metal solution in an amount of 0.01 to 10 mol % based on a total amount of the aqueous transition metal solution; and performing co-precipitation by adding a strong base to the mixed solution.

12. The method according to claim 11, wherein the transition metal salt is a sulfate, and the strong base is sodium hydroxide.

13. The method according to claim 12, wherein the sulfate is at least one selected from the group consisting of nickel sulfate, cobalt sulfate, and manganese sulfate.

14. A cathode active material prepared by mixing the transition metal precursor according to claim 1 and a lithium precursor and sintering the mixture in an oxidizing atmosphere.

15. The cathode active material according to claim 14, wherein the cathode active material comprises lithium transition metal oxide particles and carbon present in the particles and/or on surfaces of the particles.

16. A lithium secondary battery comprising the cathode active material according to claim 14.

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 drawing, in which:

(2) FIG. 1 is a scanning electron microscopy (SEM) image of a precursor prepared according to Example 1, which was captured using FE-SEM (model S-4800 available from Hitachi); and

(3) FIG. 2 is an SEM image of a precursor prepared according to Comparative Example 1, which was captured using FE-SEM (model S-4800 available from Hitachi).

BEST MODE

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

Example 1

(5) A 4 L wet reactor tank was filled with 3 L of distilled water and was continuously purged with nitrogen gas at a rate of 2 L/min to remove dissolved oxygen. Distilled water in the tank was maintained at a temperature of 45 to 50 C. using a thermostat. In addition, the distilled water in the tank was stirred at 1000 to 1200 rpm using an impeller connected to a motor installed outside the tank.

(6) Manganese sulfate, nickel sulfate, and cobalt sulfate were mixed in a molar ratio of 0.5:0.4:0.1 to prepare a 1.5 M aqueous transition metal solution. Thereafter, 2 mol % of sucrose was mixed therewith. Separately, a 3M aqueous sodium hydroxide solution was prepared. The aqueous transition metal solution was continuously pumped into the wet reactor tank, using a metering pump, at a rate of 0.18 L/hr. The aqueous sodium hydroxide solution was pumped in a rate-variable manner by a control unit for adjusting a pH of the distilled water in the tank such that the distilled water in the wet reactor tank was maintained at a pH of 11.0 to 11.5. In this regard, a 30% ammonia solution as an additive was continuously co-pumped to the reactor at a rate of 0.035 to 0.04 L/hr.

(7) Flow rates of the aqueous transition metal solution, the aqueous sodium hydroxide solution, and the ammonia solution were adjusted such that an average residence time of the solutions in the wet reactor tank was approximately 5 to 6 hours. After the reaction in the tank reached a steady state, a certain duration of time was given to synthesize a composite transition metal precursor with a higher density.

(8) After reaching the steady state, the nickel-cobalt-manganese composite transition metal precursor, which was prepared by 20-hour continuous reaction between transition metal ions of the transition metal aqueous solution, hydroxide ions of the sodium hydroxide, and ammonia ions of the ammonia solution, was continuously obtained through an overflow pipe installed on the top side of the tank.

(9) The resulting composite transition metal precursor was washed several times with distilled water and dried in a 120 C. constant-temperature drying oven for 24 hours to obtain a nickel-cobalt-manganese composite transition metal precursor.

Example 2

(10) A transition metal precursor was prepared in the same manner as in Example 1, except that 0.5 mol % of sucrose was mixed with the aqueous transition metal solution.

Example 3

(11) A transition metal precursor was prepared in the same manner as in Example 1, except that 1 mol % of sucrose was mixed with the aqueous transition metal solution.

Example 4

(12) A transition metal precursor was prepared in the same manner as in Example 1, except that 5 mol % of sucrose was mixed with the aqueous transition metal solution.

Example 5

(13) A transition metal precursor was prepared in the same manner as in Example 1, except that 2 mol % of glucose was mixed with the aqueous transition metal solution.

Example 6

(14) A transition metal precursor was prepared in the same manner as in Example 1, except that 2 mol % of lactose was mixed with the aqueous transition metal solution.

Example 7

(15) A transition metal precursor was prepared in the same manner as in Example 1, except that manganese sulfate, nickel sulfate, and cobalt sulfate were mixed in a molar ratio of 0.6:0.25:0.15 to prepare a 1.5 M aqueous transition metal solution.

Comparative Example 1

(16) A transition metal precursor was prepared in the same manner as in Example 1, except that sucrose was not mixed with the aqueous transition metal solution.

Comparative Example 2

(17) A transition metal precursor was prepared in the same manner as in Example 1, except that 20 mol % of sucrose was mixed with the aqueous transition metal solution.

Comparative Example 3

(18) A transition metal precursor was prepared in the same manner as in Example 7, except that sucrose was not mixed with the aqueous transition metal solution.

Experimental Example 1

(19) SEM images of the transition metal precursors prepared according to Example 1 and Comparative Example 1, respectively, captured using FE-SEM (model S-4800 available from Hitachi), are illustrated in FIGS. 1 and 2.

(20) Referring to FIGS. 1 and 2, it can be confirmed that the transition metal precursor of Example 1 using 2 mol % of sucrose exhibited stronger cohesive strength of primary particles than that of the precursor of Comparative Example 1 and thus particles of the precursor of Example 1 had a more spherical shape.

Experimental Example 2

(21) Each of the nickel-cobalt-manganese composite transition metal precursors of Examples 1 to 7 and Comparative Examples 1 to 3 was mixed with Li.sub.2CO.sub.3 in accordance with the molar ratio of each composition and then sintered at 950 C. for 10 hours by heating at a heating rate of 5 C./min to prepare a cathode active material powder.

(22) The prepared cathode active material powder, Denka as a conductive material, and KF1100 as a binder were mixed in a weight ratio of 95:2.5:2.5 to prepare a slurry. The slurry was uniformly coated on Al foil having a thickness of 20 m. The coated Al foil was dried at 130 C., thereby completing fabrication of a cathode for a lithium secondary battery.

(23) The fabricated cathode for a lithium secondary battery, lithium metal foil as a counter electrode (i.e., an anode), a polyethylene membrane 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 2016 coin cell.

(24) Electrical properties of the cathode active material of each of the manufactured coin cells were evaluated at 3.0 to 4.25 V using an electrochemical analyzer (Toscat 3100U available from Toyo Systems).

(25) To evaluate performance of each coin cell, charge and discharge capacities of each coin cell were measured at a voltage range of 2.75 to 4.75 V. Results of discharge capacities and charge and discharge efficiencies of the coin cells are shown in Table 1 below.

(26) In addition, to evaluate rate characteristics, the manufactured coin cells were charged at a current of 0.5 C and a voltage range of 2.75 to 4.4 V and then discharged at a current of 1 C and discharge capacities thereof were measured. Measurement results are shown in Table 1 below.

(27) TABLE-US-00001 TABLE 1 Initial charge and Initial charge and Discharge discharge discharge capacity at 1 C Sample capacity (mAh/g) efficiency (%) (mAh/g) Example 1 228.0 84.9 170.4 Example 2 218.2 83.8 167.0 Example 3 226.2 84.6 169.2 Example 4 215.3 83.4 163.0 Example 5 227.2 84.5 171.2 Example 6 224.8 84.1 168.7 Example 7 236.5 78.0 170.9 Comparative 213.4 83.1 160.0 Example 1 Comparative 82.0 84.0 31.0 Example 2 Comparative 213.1 73.6 145.4 Example 3

(28) Referring to Table 1, it can be confirmed that the coin cells according to the present invention each including the precursor treated with a particular amount of sucrose exhibited enhanced charge and discharge characteristics and rate characteristics and, in particular, the coin cell of Example 1 including the precursor treated with 2 mol % of sucrose exhibited optimum performance.

(29) Although 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.