Anode active material and method of preparing the same
Provided are a porous silicon-based anode active material including a core part including silicon (Si) and M x Si y , and a shell part including Si and a plurality of pores on the core part, wherein, in the M x Si y , M is at least one element selected from the group consisting of Group 2A, 3A, and 4A elements and transition metals, 1≤x≤4, and 1≤y≤4, and a method of preparing the porous silicon-based anode active material. According to an embodiment of the present invention, capacity characteristics and lifetime characteristic of a lithium secondary battery may be improved by minimizing the volume expansion of an anode active material during charge and discharge.
1. An anode active material comprising:
a core part consisting of silicon (Si) and M x Si y , without pores; and
a shell part including Si and a plurality of pores on the core part,
wherein, in the M x Si y , M is at least one element selected from Group 2A, 3A, or 4A elements or transition metals, 1≤x≤4, and 1≤y≤4, and
wherein a volume ratio of the core part to the shell part is in a range of 1:1 to 1:20.
2. The anode active material of claim 1 , further comprising a carbon coating layer on the shell part,
wherein the carbon coating layer has a curved portion along an uneven surface of the shell part which is formed by the pores of the shell part.
3. The anode active material of claim 2 , wherein a thickness of the carbon coating layer is in a range of 5 nm to 500 nm.
4. The anode active material of claim 2 , wherein an amount of carbon in the carbon coating layer is in a range of 2 wt % to 70 wt % based on a total weight of the anode active material.
5. The anode active material of claim 1 , wherein a weight ratio of M:Si in the M x Si y is in a range of 1:0.5 to 1:10.
6. The anode active material of claim 1 , wherein M is at least one element selected from tin (Sn), aluminum (Al), lead (Pb), indium (In), nickel (Ni), cobalt (Co), silver (Ag), magnesium (Mg), copper (Cu), germanium (Ge), chromium (Cr), titanium (Ti), manganese (Mn), vanadium (V), molybdenum (Mo), or iron (Fe).
7. The anode active material of claim 1 , wherein an average diameter of the pores is in a range of 10 nm to 2 μm as measured on a surface of the anode active material.
8. The anode active material of claim 1 , wherein an internal porosity of the shell part is in a range of 20% to 80%.
9. The anode active material of claim 1 , wherein the shell part further comprises M x Si y ,
wherein M is at least one element selected from Group 2A, 3A, or 4A elements or transition metals, 1≤x≤4, and 1≤y≤4.
10. The anode active material of claim 1 , wherein an average particle diameter (D 50 ) of the anode active material is in a range of 0.1 μm to 50 μm.
11. The anode active material of claim 1 , wherein a specific surface area (Brunauer-Emmett-Teller (BET)-SSA) of the anode active material is in a range of 2 m 2 /g to 80 m 2 /g.
12. A method of preparing the anode active material of claim 1 , the method comprising:
preparing Si-M x Si y alloy powder by using metal (M) and silicon (Si); and
preparing silicon-based particles having a core part including Si and M x Si x without pores and having a shell part including Si and a plurality of pores on the core part,
wherein the shell part is formed by removing M x Si y from a surface of the Si-M x Si y alloy powder through etching by mixing and stirring the Si-M x Si y alloy powder with an etching solution,
wherein, in the M x Si y , M is at least one element selected from Group 2A, 3A, or 4A elements or transition metals, 1≤x≤4, and 1≤y≤4, and
wherein a volume ratio of the core part to the shell part is in a range of 1:1 to 1:20.
13. The method of claim 12 , further comprising forming a carbon coating layer on surfaces of the porous silicon-based particles, after the etching.
14. The method of claim 13 , wherein the carbon coating layer is formed by mixing the porous silicon-based particles with a carbon precursor and heat treating the mixture.
15. The method of claim 14 , wherein the carbon precursor comprises gas including carbon, amorphous carbon, or low crystalline carbon.
16. The method of claim 15 , wherein the amorphous carbon or the low crystalline carbon comprises any one selected from glucose, fructose, galactose, maltose, lactose, sucrose, a phenol-based resin, a naphthalene resin, a polyvinyl alcohol resin, an urethane resin, a polyimide resin, a furan resin, a cellulose resin, an epoxy resin, a polystyrene resin, a resorcinol-based resin, a phloroglucinol-based resin, a coal-derived pitch, a petroleum-derived pitch, a tar, or low molecular weight heavy oil, or a mixture of two or more thereof.
17. The method of claim 14 , wherein the heat treatment is performed in a temperature range of 160° C. to 1,300° C.
18. The method of claim 13 , wherein the carbon coating layer is formed by a method of carburizing an amorphous carbon precursor or a chemical vapor deposition (CVD) method that uses gas including carbon.
19. The method of claim 12 , wherein the Si-M x Si y alloy powder is prepared by rapid cooling an alloy melt in which metal (M) and Si are melted.
20. The method of claim 19 , further comprising mechanical milling the prepared Si-M x Si y alloy powder between the rapid cooling and the etching.
21. The method of claim 19 , wherein the melting is performed in a temperature range of room temperature to 1,600° C.
22. The method of claim 19 , wherein the rapid cooling is performed at a rate of 10 3 K/sec to 10 9 K/sec.
23. The method of claim 12 , wherein the Si-M x Si y alloy powder is prepared by mechanical milling metal (M) and Si.
24. The method of claim 12 , further comprising performing a heat treatment before the etching, after the preparing of the Si-M x Si y alloy powder.
25. The method of claim 24 , wherein the heat treatment is performed in a temperature range of 500° C. to 800° C.
26. The method of claim 12 , wherein the etching time is in a range of 30 minutes to 1,000 minutes.
27. The method of claim 12 , wherein a concentration of the etching solution is in a range of 1M to 20 M.
28. The method of claim 12 , wherein the etching solution comprises at least one solution selected from hydrogen fluoride (HF), fluorosilicic acid (H 2 SiF 6 ), ammonium fluoride (NH 4 F), hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid.
29. An anode comprising the anode active material of claim 1 .
30. The anode of claim 29 , wherein a carbon-based material is further mixed and included in the anode active material.
31. The anode of claim 30 , wherein the carbon-based material comprises at least one selected from natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads (MCMB), carbon fibers, or carbon black.
32. A lithium secondary battery comprising:
a cathode;
an anode; and
a separator disposed between the cathode and the anode,
wherein the anode is the anode of claim 29 .