Lithium metal complex oxide and manufacturing method of the same

Abstract

The present invention relates to a lithium metal complex oxide and a preparation method thereof, and more particularly, to a lithium metal complex oxide mixed with a metal compound for a lithium reaction, stirred and heat-treated to allow residual lithium and a metal compound for reducing lithium (or a metal compound for lithium reduction) to react with each other on a surface to form a product, which is included in the lithium metal complex oxide, in which the content of Ni.sup.3+ is higher than the content of Ni.sup.2+ and a ratio of Ni.sup.3+/Ni.sup.2+ is 1.5 or greater so that life characteristics and capacity characteristics are improved, while residual lithium is reduced, and a preparation method thereof.

Claims

1. A lithium metal complex oxide comprising: Ni.sup.3+ and Ni.sup.2+, wherein a ratio of a content of Ni.sup.3+ to a content of Ni.sup.2+ is 1.5 or greater on a surface of the lithium metal complex oxide, wherein the lithium metal complex oxide comprises an oxide represented by Chemical Formula 1 below and a lithium compound represented by Chemical Formula 2 below, wherein the lithium compound represented by the Chemical Formula 2 below is disposed on the surface of the oxide represented by the Chemical Formula 1 below, and wherein the lithium compound represented by the Chemical Formula 2 below has a crystal structure different from a crystal structure of the oxide represented by the Chemical Formula 1 below:
Li.sub.1+aNi.sub.1-x-yM1.sub.xM2.sub.yO.sub.2,  <Chemical Formula 1> where M1 is Co or Mn, M2 is one or more elements selected from the group consisting of Al, Mn, Mg, Si, P, V, W, Zr, Ba, and Ga, −0.2≤a≤0.5, 0.01≤x≤0.5, and 0.01≤y≤0.2, and
Li a′-M″c-Od, and  <Chemical Formula 2> where the lithium compound represented by the Chemical Formula 2 is one selected from the group consisting of LiTi.sub.7O.sub.4 and LiTi.sub.2O.sub.4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other aspects, 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) FIG. 1 illustrates an action of Ni.sup.2+ and Ni.sup.3+ in a layered cathode active material.

(3) FIG. 2 is a graph illustrating a result of measuring a distribution of Ni.sup.2+ and Ni.sup.3+ in a lithium metal complex oxide prepared in an embodiment of the present invention through XPS.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(4) Hereinafter, examples of the present invention will be described in detail. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Any technical concept having substantially the same constitution as the technical idea described in the claims of the present invention and achieving the same operational effect is included in the scope of the present invention.

<Inventive Example> Preparation of Lithium Metal Complex Oxide

(5) Precursors represented by NiCo(OH).sub.2 and NiCoAl(OH).sub.2 were prepared to prepare a lithium metal complex oxide by a coprecipitation reaction.

(6) LiOH and Li.sub.2CO.sub.3 were added as lithium compounds to the prepared precursors and heat-treated to prepare a cathode active material for a lithium secondary battery.

(7) Co(OH).sub.2, CoOOH, Co.sub.3O.sub.4, and CoSO.sub.4 were mixed with the prepared lithium metal complex oxide and the compound for lithium reduction and the mixture was stirred, while applying energy thereto.

(8) The compound for lithium reduction mixed with the lithium metal complex oxide prepared thusly are shown in Table 1 below.

(9) TABLE-US-00001 TABLE 1 Lithium metal complex Compound for oxide lithium reduction Rinsing Inventive LiNi.sub.1−(x+y)Co.sub.xAl.sub.yO.sub.2 Co.sub.3O.sub.4 x Example-1 Inventive LiNi.sub.1−(x+y)Co.sub.xAl.sub.yO.sub.2 CoOOH x Example-2 Inventive LiNi.sub.1−(x+y)Co.sub.xAl.sub.yO.sub.2 Co(OH).sub.2 x Example-3 Comparative LiNi.sub.1−(x+y)Co.sub.xAl.sub.yO.sub.2 Co.sub.3O.sub.4, CoSO.sub.4 ∘ Example-1 Comparative LiNi.sub.1−(x+y)Co.sub.xAl.sub.yO.sub.2 x ∘ Example-2 Comparative LiNi.sub.1−(x+y)Co.sub.xAl.sub.yO.sub.2 x x Example-3

Comparative Example

(10) A cathode active material of Comparative Example 1 was prepared in the same manner as that of Inventive Example 1, except that rinsing was performed with a solution including Co.sub.3O.sub.4 or CoSO.sub.4 salt after the active material was prepared.

(11) A cathode active material of Comparative Example 2 was prepared by performing rinsing with distilled water not including cobalt after the active material was prepared without mixing Co.sub.3O.sub.4 as a compound for lithium reduction.

(12) A cathode active material of Comparative Example 3 was prepared without mixing a compound for lithium reduction and without performing rinsing after the active material was prepared.

<Experimental Example> XPS Measurement

(13) XPS of the cathode active materials for a secondary battery prepared in the above Inventive Examples and Comparative Examples was measured and results thereof are shown in FIG. 2 and Table 2 below.

(14) It can be seen that, in the case of solid phase mixing with the compound for lithium reduction without rinsing according to the present invention, the content of Ni.sup.3+ was significantly increased, relative to Ni.sup.2+, and the ratio of Ni.sup.3+/Ni.sup.2+ was the highest.

(15) TABLE-US-00002 TABLE 2 XPS analysis Classification Ni.sup.3+ Ni.sup.2+ Ni.sup.3+/Ni.sup.2+ Inventive Example-1 66.0% 34.0% 1.94 Comparative 44.1% 55.9% 0.79 Example-1 Comparative 32.4% 67.6% 0.48 Example-2 Comparative 53.7% 46.3% 1.16 Example-3

<Experimental Example> Measurement of Residual Lithium

(16) Residual lithium of the cathode active materials prepared according to the above Inventive Examples and Comparative Examples was measured.

(17) Specifically, 10 g of a prepared lithium metal complex oxide was immersed in 100 g of distilled water and stirred for 10 minutes. After stirring was finished, the product was filtered to obtain a filtrate, to which 0.1 M of HCl solution was added to be titrated to pH 5.

(18) Here, the volume of the added HCl solution was measured to analyze residual lithium of the cathode active materials for a secondary battery, and results thereof are illustrated in Table 3 below.

(19) TABLE-US-00003 TABLE 3 Residual lithium (ppm) Classification LiOH Li.sub.2Co.sub.3 free Li Inventive Example-1 5021 6990 0.178 Inventive Example-2 4948 7270 0.178 Inventive Example-3 5012 6978 0.178 Comparative 1311 1598 0.045 Example-1 Comparative 629 1628 0.026 Example-2 Comparative 7033 9914 0.250 Example-3

<Manufacturing Example> Manufacturing of Battery

(20) A battery was prepared using the cathode active materials prepared in the above Inventive Examples and Comparative Examples.

(21) First, a secondary battery cathode active material, super-P as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a weight ratio of 95:5:3 to prepare a slurry. The prepared slurry was uniformly applied to an aluminum foil having a thickness of 15 μm and vacuum-dried at 135° C. to prepare a cathode for a lithium secondary battery.

(22) A coil battery was manufactured using the obtained cathode for a lithium secondary battery, a lithium foil as a counterpart electrode, a porous polyethylene film (Celguard LLC., Celguard 2300) having a thickness of 25 μm as a separator, and a solvent including ethylene carbonate and ethylmethylcarbonate mixed in the volume ratio of 3:7 and including LiPF.sub.6 having a concentration of 1.15M as a liquid electrolyte.

<Experimental Example> Measurement of Battery Characteristics—Capacity Characteristics

(23) Initial capacities of batteries including the cathode active materials of the present invention prepared in Inventive Examples and cathode active materials of Comparative Examples were measured and results thereof are shown in Table 4.

(24) TABLE-US-00004 TABLE 4 1.sup.st charge/discharge (0.15 C., 3.0~4.25 V @25° C.) Charge Discharge Efficiency Classification mAh/g mAh/g % Inventive Example-1 229.5 205.8 89.7 Inventive Example-2 229.0 205.4 89.7 Inventive Example-3 229.2 205.2 89.5 Comparative 230.2 201.1 87.4 Example-1 Comparative 229.1 199.4 87.0 Example-2 Comparative 230.1 203.9 88.6 Example-3

<Experimental Example> Measurement of Battery Characteristics—Life Characteristics and High-Temperature Storage Characteristics

(25) Life characteristics and high-temperature storage characteristics of the batteries including the cathode active materials of the present invention prepared in Inventive Examples and the cathode active materials of Comparative Examples were measured by resistance before and after storage, and results thereof are shown in Table 5 and Table 6.

(26) TABLE-US-00005 TABLE 5 Life time (@100 cycle) Room temperature ((1 C., 3.0~4.25 V) Classification % Inventive Example-1 93.1 Inventive Example-2 93.3 Inventive Example-3 93.9 Comparative Example-1 78.9 Comparative Example-2 72.3 Comparative Example-3 87.8

(27) TABLE-US-00006 TABLE 6 Life time lmp 1st 100th Classification Ω Ω Inventive Example-1 2.9 12.3 Inventive Example-2 2.0 11.3 Inventive Example-3 1.9 11.5 Comparative Example-1 3.6 19.9 Comparative Example-2 22.0 51.5 Comparative Example-3 4.7 37.6
In Table 5 and Table 6, it can be seen that the life characteristics of Inventive Examples according to the present invention were significantly improved, as compared with Comparative Examples.