ANODE ACTIVE MATERIAL, LITHIUM SECONDARY BATTERY COMPRISING SAME, AND METHOD FOR PREPARING ANODE ACTIVE MATERIAL

Abstract

The present invention provides an anode active material and a method for preparing the same, wherein the anode active material has a core-shell structure having formula (MOx-Liy)-C (here, M is a metal (or metalloid), x is greater than 0 and less than 1.5, and y is greater than 0 and less than 4) and including a core part containing an alloy of a metal (or metalloid) oxide-Li (MOx-Liy) and a shell part containing a carbon material coated on a surface of the core part, wherein the shell part contains lithium in an amount less than 5 atm % in the surface and the inner portion thereof. The anode active material can provide high capacity, excellent cycle characteristics, excellent volume expansion control capability, and high initial efficiency.

Claims

1. An anode active material, having a core-shell structure of formula (MO.sub.x—Li.sub.y)—C (where, M is a metal (or metalloid), x is greater than 0 and less than 1.5, and y is greater than 0 and less than 4), which includes a core part containing an alloy of a metal (or metalloid) oxide-Li (MO.sub.x—Li.sub.y) and a shell part containing a carbon material coated on a surface of the core part, wherein the shell part contains lithium in an amount less than 5 at % in the surface and the inner portion thereof.

2. The anode active material of claim 1, wherein the shell part has a thickness of 20 nm to 60 nm.

3. The anode active material of claim 1, wherein the metal (or metalloid) is selected from a group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga, and an alloy thereof.

4. The anode active material of claim 1, wherein the metal (or metalloid) is any one selected from a group consisting of SiO, SnO, SnO.sub.2 and a mixture thereof.

5. The anode active material of claim 1, wherein the core part has a diameter of 0.05 μm to 30 μm.

6. The anode active material of claim 1, wherein the carbon material is crystalline carbon, amorphous carbon, or a mixture thereof.

7. The anode active material of claim 1, wherein the carbon material of the shell part is present in an amount of 0.05 wt % to 30 wt % based on the weight of the anode active material.

8. A method for preparing an anode active material having a core-shell structure of formula (MO.sub.x—Li.sub.y)—C (where, M is a metal (or metalloid), x is greater than 0 and less than 1.5, and y is greater than 0 and less than 4), the method comprising steps of: (S1) coating a carbon material on the surface of a core part containing an oxide of metal (or metalloid); (S2) mixing the material obtained in the step of (S1) with a lithium metal powder, followed by thermal treatment to carry out alloying of lithium and the metal (or metalloid); and (S3) bringing the material obtained in the step of (S2) into acid-treatment.

9. The method of claim 8, wherein the anode active material having the core-shell structure has pH 7 to 10 in a water-based system.

10. The method of claim 8, wherein the acid-treatment is carried out using at least one acid selected from a group consisting of hydrochloric acid (HCl), perchloric acid, nitric acid, and sulfuric acid.

11. The method of claim 8, wherein the acid used in the acid-treatment has a concentration of 0.5 M to 3 M.

12. The method of claim 8, wherein the acid-treatment is carried out for 0.5 to 5 hours.

13. The method of claim 8, wherein the metal (or metalloid) is selected from a group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga, and an alloy thereof.

14. The method of claim 8, wherein the metal (or metalloid) is any one selected from a group consisting of SiO, SnO, SnO2 and a mixture thereof.

15. The method of claim 8, wherein the core part has a diameter of 0.05 μm to 30 μm.

16. The method of claim 8, wherein the carbon material is crystalline carbon, amorphous carbon, or a mixture thereof.

17. The method of claim 8, wherein the carbon material of the shell part is present in an amount of 0.05 wt % to 30 wt % based on the weight of the anode active material.

18. The method of claim 8, wherein in the alloying step of lithium and the metal (or metalloid), the material obtained in the step of (S1) and the lithium metal powder is used in a weight ratio of 70:30 to 98:2.

19. An anode for a lithium secondary battery, comprising: a current collector, and an anode active material layer formed on at least one surface of the current collector and comprising the anode active material of claim 1.

20. A lithium secondary battery, comprising: a cathode, the anode of claim 19, and a separator interposed between the cathode and the anode.

Description

PREPARATIVE EXAMPLES

[0081] 10 g of SiO having an average particle diameter of 5 μm as a metal (or metalloid) oxide was put into a rotary tube furnace, and the temperature of the furnace was increased to 1000° C. at a rate of 5° C./min after flowing argon gas at a rate of 0.5 L/min. Thermal treatment was performed for 2 hours while rotating the rotary tube furnace at a rate of 10 rpm/min and flowing argon gas at a rate of 1.8 L/min and acetylene gas at a rate of 0.3 L/min, to manufacture a composite having carbon coating layer on the surface of SiO as a core part.

[0082] The carbon coating layer had a carbon content of 5.3 parts by weight based on 100 parts by weight of the core part. Also, it was observed from TEM analysis that the carbon coating layer was 40 nm thick.

[0083] The manufactured composite was mixed with lithium metal powder at a weight ratio of 92:8 to form a mixture. The mixture was thermally treated at 700° C. for 5 hours under Ar atmosphere to alloy the lithium with the core part.

Examples 1 to 4, and Comparative Examples 1 to 6

[0084] It was aimed to remove a by-product of lithium from the alloyed composite prepared in the preparative example with HCl, by performing etching in the form of a batch, accompanied with stirring.

[0085] The removal of the by-product of lithium may involve removal of a portion or the entire portion of the lithium by-product from the carbon coating layer.

[0086] The removal was performed while varing the concentration of the used HCl and etching time, and the results are shown in Table 1 below.

Comparative Example 7

[0087] The alloyed composite according to the Preparative Example was washed with distilled water.

TABLE-US-00001 TABLE 1 HCl Concentration (M) Etching Time (Hr) Preparative Example 1 0.5 5 Preparative Example 2 2 3 Preparative Example 3 3 0.5 Preparative Example 4 0.5 2 Comparative Example 1 0.1 0.5 Comparative Example 2 0.1 24 Comparative Example 3 6 0.5 Comparative Example 4 6 10 Comparative Example 5 6 24 Comparative Example 6 — —

[0088] Initial efficiency of the active material and gas generation of the water-based slurry in Examples 1 to 4 and Comparative Examples 1 to 5 of the above Table 1 were measured, and the results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Initial efficiency (%) Gas generation Example 1 87.4 X Example 2 87.4 X Example 3 87.0 X Example 4 87.9 X Comparative Example 1 88 ◯ Comparative Example 2 80 X Comparative Example 3 77 X Comparative Example 4 76 X Comparative Example 5 76 X

[0089] As shown in the above Table 2, the anode active material of Examples 1 to 4 according to the present disclosure suppressed gas generation in the water-based slurry and had higher initial efficiency.

[0090] Lithium atom % was measured according to etching depth of the anode active material prepared in Examples 2 and 4 and Comparative Examples 4 and 6, and the results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Etching depth (nm) Lithium at % Example 2 0 1.7 25 2.1 50 3.2 100 11 Example 4 0 1.2 25 2.1 50 9.8 100 11.4 Comparative Example 0 1 4 25 1 50 1.1 100 1.2 Comparative Example 0 9.9 6 25 7.8 50 9.8 100 12.3

[0091] As shown in Table 3 above, Examples 2 and 4 of the present disclosure removed a significant amount of the lithium by-product of the shell part, while Comparative Example 4 removed lithium of the core part by the treatment at high concentration of the acid for a long time and Comparative Example 6 did not remove the lithium by-product.

[0092] A pH of the anode active material in Examples 1 to 4 and Comparative Examples 4 and 6 were measured, and the results are provided in Table 4 below.

TABLE-US-00004 TABLE 4 pH Example 1 9.8 Example 2 9.7 Example 3 8.75 Example 4 10 Comparative Example 1 10.8 Comparative Example 2 6.9 Comparative Example 3 6.9 Comparative Example 4 6.8 Comparative Example 6 13.6 Comparative Example 7 11.2

[0093] As shown in Table 4 above, Examples 1 to 4 had the pH range listed above as the lithium by-product was removed. However, Comparative Examples 1 to 4 had a relatively lower pH and Comparative Examples 6 and 7 had a relatively higher pH, and the lithium by-product were not properly removed.

[0094] The present disclosure has been described in detail. However, it should be, understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, and various changes and modifications in the scope of the disclosure will become apparent to those skilled in the art from this detailed description.