Si/C composite, method of preparing the same, and anode active material for lithium secondary battery including the Si/C composite
Provided are a Si/C composite, in which carbon (C) is dispersed in an atomic state in a silicon (Si) particle, and a method of preparing the Si/C composite. Since the Si/C composite of the present invention is used as an anode active material, electrical conductivity may be further improved and volume expansion may be minimized. Thus, life characteristics of a lithium secondary battery may be improved.
1. A method of preparing a Si/C composite, the method comprising:
i) mixing an aromatic group-containing silicon alkoxide compound expressed by Chemical Formula 1 with an organic solvent to form a SiO 2 /C composite;
ii) mixing the SiO 2 /C composite obtained in step i) with an alkali metal or an alkaline earth metal and heat treating the mixture in an inert atmosphere to reduce SiO 2 ; and
iii) acid treating the heat-treated product obtained in step ii) to remove an oxide,
SiR 1 n R 2 4−n <Chemical Formula 1>
wherein
R 1 is a phenyl group,
R 2 is an alkoxy group of C 1 to C 4 , and
n is 1 to 3,
wherein carbon in the SiO 2 /C composite is generated from the aromatic group-containing silicon alkoxide compound, and
wherein an amount of the carbon in the SiO 2 /C composite is adjusted according to an amount of the aromatic group-containing silicon alkoxide compound.
2. The method of claim 1 , wherein the aromatic group-containing silicon alkoxide compound is any one selected from phenyltriethoxysilane (PTES), phenyltrimethoxysilane (PTMS), diphenyldiethoxysilane (DDES), or a mixture of two or more thereof.
3. The method of claim 2 , wherein the aromatic group-containing silicon alkoxide compound is PTES.
4. The method of claim 1 , wherein an amount of the aromatic group-containing silicon alkoxide compound is in a range of 0.1 parts by weight to 20 parts by weight based on the organic solvent.
5. The method of claim 1 , further comprising adding a linear silicon alkoxide compound to the organic solvent in step i).
6. The method of claim 5 , wherein the linear silicon alkoxide compound is any one selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrapropyl orthosilicate (TPOS), tetrabutyl orthosilicate (TBOS), or a mixture of two or more thereof.
7. The method of claim 6 , wherein the linear silicon alkoxide compound is TEOS or TMOS.
8. The method of claim 5 , wherein a mixing ratio of the aromatic group-containing silicon alkoxide compound to the linear silicon alkoxide compound is in a range of 1:0.3 to 1:60 as a molar ratio.
9. The method of claim 1 , wherein the alkali metal is lithium, sodium, potassium, rubidium, cesium, or francium.
10. The method of claim 1 , wherein the alkaline earth metal is beryllium, magnesium, calcium, strontium, barium, or radium.
11. The method of claim 1 , wherein the heat treatment of step ii) is performed in a temperature range of 350° C. to 1400° C.
12. The method of claim 1 , further comprising coating a surface of the Si/C composite with carbon by mixing the Si/C composite with a carbon precursor after step iii).
13. The method of claim 12 , wherein the coating is performed in a temperature range of 300° C. to 1400° C.
14. The method of claim 12 , wherein the carbon precursor is pitch or a hydrocarbon-based material.