Patent ID: 7658871

Claim:
A method of preparing a negative active material for a rechargeable lithium battery comprising: first alloying Si and element M by a mechanical alloying process to provide a SiM alloy, wherein M is selected from the group consisting of Ni, Co, B, Cr, Cu, Fe, Mn, Ti, Y and combinations thereof; first heating the SiM alloy at a first temperature, wherein the first temperature is below a melting point of the SiM alloy; adding a powder of element X to the heated SiM alloy wherein X is selected from the group consisting of Ag, Cu, Au and combinations thereof, provided that if M is Cu, X is not Cu; second alloying the combined SiM alloy and element X by a mechanical alloying process to provide a SiMX alloy; and second heating the SiMX alloy at a second temperature lower than the first temperature; wherein the negative active material comprises a Si phase, a SiM phase and at least one of an X phase and a SiX phase, wherein each of the phases has a crystal grain size between 100 nm and 500 nm.