Composite anode active material, anode including the same, and lithium secondary battery including the anode

1. A composite anode active material comprising:

a core comprising silicon, wherein the core has a porosity of about 1% to about 10%; and

a carbonaceous shell,

wherein the carbonaceous shell comprises a carbonaceous material and a lithium titanium oxide represented by Formula 1

Li x+3 Ti y O 12   Formula 1

wherein 2.4≤x≤4.2 and 4.8<y<6.6, and

wherein the lithium titanium oxide of Formula 1 is

inert to oxidation or reduction between 1 volt to 4.3 volts versus Li/Li + .

2. The composite anode active material of claim 1 , wherein the lithium titanium oxide is dispersed in the carbonaceous material.

3. The composite anode active material of claim 1 , wherein the core comprises at least one of Si, SiO x where 0<x<2, a Si—C composite, or a Si alloy.

4. The composite anode active material of claim 3 , wherein the Si alloy comprises at least one of Fe 3 Si, Fe 2 Si, Fe 5 Si 3 , FeSi, FeSi 2 , FeSi 3 , AlSi 2 , Cu 5 Si, Mg 2 Si, NiSi, TiSi 2 , or Si 7 Ti 4 Ni 4 .

5. The composite anode active material of claim 1 , wherein the lithium titanium oxide of Formula 1 has an electrical conductivity of at least 10 Siemens per meter.

6. The composite anode active material of claim 1 , wherein the lithium titanium oxide comprises Li 7 Ti 5 O 12 .

7. The composite anode active material of claim 1 , wherein the carbonaceous shell further comprises a titanium-containing compound represented by Formula 4:

Ti y M z O n   Formula 4

wherein 1≤y≤2, 0≤z≤2, 1≤n≤7, and

M is at least one of Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb, or As.

8. The composite anode active material of claim 7 , wherein the titanium-containing compound comprises at least one of TiO 2 , TiSO 5 , or TiP 2 O 7 .

9. The composite anode active material of claim 1 , wherein the carbonaceous material comprises at least one of crystalline carbon or amorphous carbon.

10. The composite anode active material of claim 1 , wherein an amount of the carbonaceous shell is in a range of about 0.1 parts by weight to about 50 parts by weight, with respect to 100 parts by weight of the core.

11. The composite anode active material of claim 1 , wherein an amount of the lithium titanium oxide is in a range of about 0.1 parts by weight to about 50 parts by weight, with respect to 100 parts by weight of the carbonaceous material.

12. An anode comprising the composite anode active material according to claim 1 .

13. The anode of claim 12 , wherein the anode further comprises an additional anode active material.

14. A lithium secondary battery comprising the anode according to claim 12 .

15. A method of preparing a composite anode active material, the method comprising:

providing a core comprising silicon, wherein the core has a porosity of about 1% to about 10%; and

contacting the core with a carbonaceous material and a lithium titanium oxide to form a carbonaceous shell comprising the carbonaceous material and the lithium titanium oxide on a surface of the core; and

intercalating lithium into the lithium titanium oxide to prepare the composite anode active material, wherein the intercalated lithium titanium oxide comprises a compound represented by Formula 1

Li x+3 Ti y O 12   Formula 1

wherein 2.4≤x≤4.2 and 4.8<y<6.6,

wherein the lithium titanium oxide of Formula 1 is a product of lithium intercalation of a lithium titanate of Formula 2 at 4.2 volts versus Li/Li + or greater

Li x Ti y O 12   Formula 2

wherein 2.4≤x≤4.2 and 4.8<y≤6.6.

16. A method of protecting a silicon anode material, the method comprising:

providing a composite anode material comprising

a core comprising silicon, wherein the core has a porosity of about 1% to about 10%, and

a carbonaceous shell comprising a carbonaceous material and lithium titanium oxide; and

intercalating lithium into the lithium titanium oxide to form an inert material on a surface of the core to protect the silicon anode material,

wherein the lithium titanium oxide comprises a compound represented by Formula 1

Li x+3 Ti y O 12   Formula 1

wherein 2.4≤x≤4.2 and 4.8<y≤6.6,

wherein the lithium titanium oxide of Formula 1 is a product of lithium intercalation of a lithium titanate of Formula 2 at 4.2 volts versus Li/Li + or greater

Li x Ti y O 12   Formula 2

wherein 2.4≤x≤4.2 and 4.8<y≤6.6.

17. The method of claim 16 , wherein the compound represented by Formula 1 is Li 7 Ti 5 O 12 .