Cathode active material and lithium secondary battery including the same

Abstract

Disclosed are a cathode active material including a lithium transition metal oxide based on at least one transition metal selected from the group consisting of Ni, Mn and Co, wherein at least one hetero element selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Bi, Zn and Zr is located at a surface portion of or inside the lithium transition metal oxide, and a secondary battery including the same. The cathode active material according to the present invention includes predetermined hetero elements at a surface thereof and therein, and, as such, a secondary battery based on the cathode active material may exhibit excellent high-speed charge characteristics and lifespan characteristics.

Claims

1. A method of preparing a lithium transition metal oxide, comprising: reacting a MnNi-containing transition metal precursor with 0.001 to 0.9 mol % M.sub.xA.sub.y to form a surface treated transition metal precursor, wherein M is at least one selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Bi, Zn, and Zr; A is at least one selected from the group consisting of O, OH, SO.sub.4, PO.sub.4, NO.sub.3, CO.sub.3, BO.sub.3, and F; and when 0<x<4 and 0<y<4, an oxidation number of M times x plus an oxidation number of A times y is 0; mixing the surface treated transition metal precursor with a lithium containing material; and sintering the mixture to form the lithium transition metal oxide based on Ni and Mn, wherein at least one hetero element selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Bi, Zn and Zr is located at a surface portion of or inside the lithium transition metal oxide.

2. The method according to claim 1, wherein M.sub.xA.sub.y is at least one selected from the group consisting of TiO.sub.2, Co.sub.3O.sub.4, Al.sub.2O.sub.3, CuO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, MgO, B.sub.2O.sub.3, Cr.sub.2O.sub.3, Ti(SO.sub.4).sub.2, CoSO.sub.4, Al.sub.2(SO.sub.4).sub.3, CuSO.sub.4, FeSO.sub.4, MgSO.sub.4, Ti.sub.3(PO.sub.4).sub.4, CoPO.sub.4, AlPO.sub.4, Mg.sub.3(PO.sub.4).sub.2, TiF.sub.4, CoF.sub.3, AlF.sub.3, CuF.sub.2, FeF.sub.3, Al(NO.sub.3).sub.3 and MgF.sub.2.

3. The method according to claim 1, wherein M.sub.xA.sub.y dissolved in water or sodium hydroxide is added to a reactor.

Description

MODE FOR INVENTION

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

Preparation Example 1

(2) <Preparation of Nickel-Manganese Composite Transition Metal Precursor>

(3) After filling a 3 L wet reactor tank with 2 L of distilled water, nitrogen gas was continuously added to the tank at a rate of 1 L/min to remove dissolved oxygen. Here, the temperature of distilled water in the tank was maintained at 45 to 50 using a temperature maintenance device. 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.

(4) Nickel sulfate, titanium sulfate and manganese sulfate were mixed in a ratio (molar ratio) of 0.25:0.04:0.71 to prepare a 2 M aqueous transition metal solution. Separately, a 4 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 10.5 to 11.0. In this regard, a 30% ammonia solution as an additive was continuously co-pumped into the reactor at a rate of 0.035 L/hr to 0.04 L/hr.

(5) 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 6 hours. After the reaction in the tank reached a steady state, reaction was allowed to proceed for a certain time to synthesize a composite transition metal precursor with a higher density.

(6) <Surface-Treatment with Titanium>

(7) After reaching the steady state, the nickel-titanium-manganese composite transition metal precursor slurry, 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 transferred to a second 2 L wet reactor tank through an overflow pipe installed on the top side of the tank. Here, to the second 2 L wet reactor tank, nitrogen gas was continuously added to prevent oxidation of the precursor, and a temperature of a reactant was maintained to 45 to 50 C. using a temperature maintenance device. In addition, the precursor slurry in the tank was stirred at 1000 to 1200 rpm using an impeller connected to a motor installed outside the tank

(8) 0.015 M titanium sulfate was dissolved in distilled water to prepare an aqueous metal solution for surface treatment and, separately, a 0.06 M aqueous sodium hydroxide solution was prepared. The aqueous metal solution for surface treatment was continuously pumped into the second wet reactor tank 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 10.5 to 11.0.

(9) A precursor slurry, surface-treatment of which had been completed in the second wet reactor, was continuously obtained through an overflow pipe. The obtained surface-treated composite transition metal precursor was washed with distilled water several times and then dried in a 120 constant temperature dryer for 24 hours. As a result, a nickel-manganese composite transition metal precursor surface-treated with titanium was obtained.

Example 1

(10) The nickel-manganese composite transition metal precursor surface-treated with titanium prepared according to Preparation Example 1 was mixed with Li.sub.2CO.sub.3 in a stoichiometric ratio and then the resulting mixture was sintered at 1000 C. for 10 hours, resulting in preparation of a lithium transition metal oxide.

Example 2

(11) A lithium transition metal oxide was prepared in the same manner as in Example 1, except that, in Preparation Example 1, aluminum nitrate as a raw material for surface treatment was used.

Example 3

(12) A lithium transition metal oxide was prepared in the same manner as in Example 1, except that, in Preparation Example 1, aluminum nitrate and ammonium fluoride as a raw material for surface treatment were used.

Comparative Example 1

(13) A lithium transition metal oxide was prepared in the same manner as in Example 1, except that, in Preparation Example 1, a process of surface-treating with titanium was omitted

Initial Charge and Discharge Characteristics

(14) A cathode using the lithium transition metal oxide prepared according to each of Examples 1 to 3 and Comparative Example 1, 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 LiPF6 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.

(15) Charge and discharge characteristics of a coin cell manufactured using each of the lithium transition metal oxides prepared according to Examples 1 to 3 and Comparative Example 1 were evaluated by charging and discharging once in a voltage range of 3.5 to 4.9 V at a current of 0.1 C. Results are summarized in Table 1 below.

(16) TABLE-US-00001 TABLE 1 Initial charge Initial discharge Initial charge and capacity capacity discharge efficiency (mAh/g) (mAh/g) (%) Example 1 147.7 138.5 93.8 Example 2 146.9 138.7 94.4 Example 3 147.6 142.3 96.4 Comparative 147.3 138.6 94.1 Example 1

High-Speed Charge Characteristics

(17) High-speed charge characteristics of a coin cell manufactured using each of the lithium transition metal oxides prepared according to Examples 1 to 3 and Comparative Example 1 were evaluated by charging at a current of 5.0 C after charging and discharging at a current of 0.1 C. Results are summarized in Table 2 below.

(18) TABLE-US-00002 TABLE 2 Charge Charge High-speed charge capacity at capacity at 5 efficiency at 0.1 C (mAh/g) C (mAh/g) 0.1 C/5.0 C (%) Example 1 147.7 134.7 91.2 Example 2 146.9 133.1 90.6 Example 3 147.6 136.1 92.2 Comparative 147.3 125.6 85.3 Example 1

Lifespan Characteristics

(19) Lifespan characteristics of a coin cell manufactured prepared using each of the lithium transition metal oxides prepared according to Examples 1 to 3 and Comparative Example 1 were evaluated by charging and discharging one-hundred times at a current of 1.0 C. Results are summarized in Table 3 below.

(20) TABLE-US-00003 TABLE 3 Lifespan characteristics Discharge capacity (%) of 100.sup.th/1.sup.st Example 1 96.8 Example 2 96.7 Example 3 97.4 Comparative 91.8 Example 1

(21) As shown in the Experimental Examples 1 to 3, it can be confirmed that the coin cells according to Examples 1 to 3 manufactured using the precursors surface-treated with the predetermined metal have excellent battery characteristics such as initial charge and discharge characteristics and the like, when compared to the coin cell manufactured according to Comparative Example 1.

INDUSTRIAL APPLICABILITY

(22) As described above, a cathode active material according to the present invention includes a predetermined lithium transition metal oxide, wherein hetero elements are located at surface portions of and inside particles of the lithium transition metal oxide, and thereby the cathode active material may be used without dramatic deterioration of electric characteristics even under high voltage, and, accordingly, a lithium secondary battery using the cathode active material may exhibit excellent high-speed charge and output characteristics, and high lifespan characteristics.

(23) 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.