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

Abstract

Disclosed are a precursor for preparation of a lithium composite transition metal oxide, a method for preparing the same and a lithium composite transition metal oxide obtained from the same. More particularly, the transition metal precursor which has a composition represented by Formula 1 below and is prepared in an aqueous transition metal solution, mixed with a transition metal-containing salt, including an alkaline material, the method for preparing the same and the lithium composite transition metal oxide obtained from the same are disclosed.
Mn.sub.aM.sub.b(OH.sub.1-x).sub.2-yA.sub.y(1) wherein M is at least one selected form the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected form the group consisting of anions of PO.sub.4, BO.sub.3, CO.sub.3, F and NO.sub.3, and 0.5a1.0; 0b0.5; a+b=1; 0<x<1.0; and 0y0.02.

Claims

1. A method of preparing a transition metal precursor comprising: preparing an aqueous transition metal solution comprising a transition metal-containing salt for preparing a precursor having a first anion; mixing a second anion selected from the group consisting of PO.sub.4, BO.sub.3, CO.sub.3, F and NO.sub.3 and a reducing agent with the aqueous transition metal solution to substitute anion sites of the precursor; and co-precipitating by adding a strong base after the mixing to form the transition metal precursor having a composition represented by Formula 1 below:
Mn.sub.aM.sub.b(OH.sub.1-x).sub.2-yA.sub.y(1) wherein M is Ni and Co; A is at least one selected from the group consisting of anions of PO.sub.4, BO.sub.3, CO.sub.3, F and NO.sub.3; 0.5a1.0; 0b0.5; a+b=1; 0<x<1.0; and 0<y0.02; wherein the reducing agent is a sugar-based material; and wherein the transition metal-containing salt consists of a transition metal cation and the first anion.

2. The method according to claim 1, wherein the reducing agent has a concentration of 2.0 to 7.0 mol % based on a molar amount of the aqueous transition metal solution.

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);

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

(4) FIG. 3 is a scanning electron microscopy (SEM) image of a precursor prepared according to Comparative Example 1, which was captured using FE-SEM (model S-4800 available from Hitachi); and

(5) FIG. 4 is a scanning electron microscopy (SEM) image of a precursor prepared according to Comparative Example 2, which was captured using FE-SEM (model S-4800 available from Hitachi).

BEST MODE

(6) Now, the present invention will be described in more detail with reference to 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

(7) After filling a 4 L wet reactor tank with 3 L of distilled water, nitrogen gas was continuously added to the tank at a rate of 2 L/min to remove dissolved oxygen. Here, the temperature of distilled water in the tank was maintained at 50 using a temperature maintenance device. In addition, the distilled water in the tank was stirred at 1000 to 1500 rpm using an impeller connected to a motor installed outside the tank.

(8) Manganese sulfate, nickel sulfate, and cobalt sulfate were mixed in a molar ratio of 0.50:0.45:0.05 to prepare a 1.5 M aqueous transition metal solution. Subsequently, to substitute anion sites, 0.5 mol % of phosphate and 4.0 mol % of sucrose which provide PO.sub.4 anions were mixed therewith. Separately, a 3 M 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 11.5. In this regard, a 14% ammonia solution as an additive was continuously co-pumped to the reactor at a rate of 0.04 L/hr.

(9) Flow rates of the aqueous transition metal solution, the aqueous sodium hydroxide solution and the aqueous ammonia solution were adjusted such that an average residence time of the solutions in the wet reactor tank was approximately 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.

(10) After reaching the steady state, the manganese-nickel composite transition metal precursor, which was prepared by 20-hour continuous reaction of transition metal ions of the aqueous transition metal 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.

(11) 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 manganese-nickel composite transition metal precursor.

Example 2

(12) 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 1

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

Comparative Example 2

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

Experimental Example 1

(15) SEM images of the transition metal precursors prepared according to Examples 1 and 2, and Comparative Examples 1 and 2, respectively, captured using FE-SEM (model S-4800 available from Hitachi), are illustrated in FIGS. 1 to 4.

(16) Referring to FIGS. 1 to 4, 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

(17) Referring to FIG. 1 to FIG. 4, it was confirmed that the precursor prepared according to Example 1, which uses sucrose and anion sites of which were substituted with PO.sub.4, has many pores, a wide specific surface area and a uniform diameter, when compared with the precursors prepared according to Comparative Examples 1 and 2. In addition, it was confirmed that, in the precursor prepared according to Example 1, primary particles exhibited improved cohesive force and thereby particle crystallizability and particle spheroidization degree were improved. Furthermore, it was confirmed that, although sucrose was not used, the precursor prepared according to Example 2, anion sites of which were substituted with PO.sub.4, exhibited improved particle crystallizability and particle spheroidization degree, when compared with the precursors prepared according to Comparative Examples 1 and 2.

Experimental Example 2

(18) The tap densities of the precursors prepared according to Examples 1 and 2, and Comparative Examples 1 and 2, respectively, were measured and summarized in Table 1 below.

(19) TABLE-US-00001 TABLE 1 Tap density (g/cc) Example 1 1.54 Example 2 0.95 Comparative 0.55 Example 1 Comparative 0.80 Example 2

(20) As shown in Table 1, it can be confirmed that the precursors prepared according to Examples 1 and 2, anion sites of which were substituted, exhibit improved tap densities, when compared with the precursors prepared according to Comparative Examples 1 and 2, anion sites of which were not substituted. Such a result is caused by easy precipitation of the transition metal hydroxide due to anion sites substituted with PO.sub.4 and thereby improved crystallizability and cohesive force of the primary particles.

Examples 3 and 4, and Comparative Examples 3 and 4

(21) Manufacture of Coin Cell

(22) Each of the manganese-nickel-cobalt composite transition metal precursors prepared according to Examples 1 and 2, and Comparative Examples 1 and 2 was mixed with Li.sub.2CO.sub.3 in accordance with the molar ratio of each composition and then sintered at 900 to 950 C. for 5 to 10 hours by heating at a heating rate of 3 to 5 C./min to prepare a cathode active material powder.

(23) 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.

(24) 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 1 M 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.

Experimental Example 3

(25) Initial Charge and Discharge Characteristics

(26) Electrical characteristics of the cathode active material of each of coin cells manufactured according to Examples 3 and 4, and Comparative Examples 3 and 4 were evaluated at 3.0 to 4.4 V using an electrochemical analyzer (Toscat 3100U available from Toyo Systems).

(27) To evaluate performance of each coin cell, charge and discharge capacity of each coin cell was measured at a current of 1 C and at a voltage range of 3.0 to 4.4 V. Results of discharge capacities and charge and discharge efficiencies of the coin cells are summarized in Table 2 below.

(28) TABLE-US-00002 TABLE 2 Initial charge Initial discharge Initial charge and capacity capacity discharge efficiency Samples (mAh/g) (mAh/g) (%) Example 3 185 172 93 Example 4 183 169 92 Comparative 169 153 90 Example 3 Comparative 180 162 90 Example 4

(29) As shown in Table 2, it can be confirmed that the precursors prepared according to Examples 1 and 2, anion sites of which were substituted, have superior initial charge and discharge capacity and efficiency, when compared with the precursors prepared according to Comparative Examples 1 and 2, anion sites of which were not substituted.

Experimental Example 4

(30) Lifespan Characteristics

(31) Each of coin cells manufactured according to Examples 3 and 4, and Comparative Examples 3 and 4 was charged and discharged thirty times at a current of 0.5 C to evaluate lifespan characteristics. Results are summarized in Table 3 below.

(32) TABLE-US-00003 TABLE 3 Lifespan characteristics 30.sup.th/1.sup.st discharge capacity (%) Example 3 97.0 Example 4 92.0 Comparative 92.2 Example 3 Comparative 96.0 Example 4

(33) As shown in Table 3, it can be confirmed that the precursor prepared according to Example 1, which uses sucrose and anion sites of which were substituted with PO.sub.4, exhibits lifespan characteristics of 97%, which is the highest value.

Experimental Example 5

(34) Output Characteristics

(35) To evaluate output characteristics, each of coin cells manufactured according to Examples 3 and 4, and Comparative Examples 3 and 4 was charged and discharged at a current of 0.5 C and then discharged at a current of 1.0 C and 2.0 C. Results are summarized in Table 4 below.

(36) TABLE-US-00004 TABLE 4 0.1 C discharge 2 C discharge Output capacity capacity characteristics (mAh/g) (mAh/g) 0.1 C/2.0 C (%) Example 3 172 146 85 Example 4 172 136 79 Comparative 155 121 78 Example 3 Comparative 166 112 67 Example 4

(37) As shown in Table 4, it can be confirmed that the precursors prepared according to Examples 1 and 2, anion sites of which were substituted, exhibit improved output characteristics when compared with the precursors prepared according to Comparative Examples 1 and 2, anion sites of which were not substituted.

(38) 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

(39) As described above, a transition metal precursor for preparing a lithium composite transition metal oxide according to the present invention is prepared in a state including a reducing agent to prevent oxidation of Mn and, as such, a precursor having a larger specific surface area and a uniform diameter may be synthesized. At the same time, by substituting anion sites, precipitation suppression due to addition of a reducing agent may be solved and, as such, the crystallizability, spheroidization degree and tap density of the precursor may be improved.

(40) In addition, when a lithium composite transition metal oxide prepared using the precursor is used as a cathode active material, an electrode process becomes easy and a secondary battery based on the lithium composite transition metal oxide may exhibit excellent initial discharge capacity and efficiency, and improved output characteristics and lifespan characteristics.