Negative active material for rechargeable lithium battery, method of preparing same and rechargeable lithium battery

Abstract

Disclosed is a negative active material for a rechargeable lithium battery comprising a Si phase, a SiM phase and at least one of a X phase and a SiX phase, wherein each of phases has a crystal grain size of 100 nm and 500 nm. The element M is at least one selected from the group consisting of Ni, Co, B, Cr, Cu, Fe, Mn, Ti, and Y, the element X is at least one selected from the group consisting of Ag, Cu, and Au. However, where M is Cu, X is not Cu.

1 . A negative active material for a rechargeable lithium battery comprising a Si phase, a SiM phase, and at least one of a X phase and a SiX phase, wherein each of phases has a crystal grain size of between 100 nm and 500 nm.  
     
     
         2 . The negative active material for a rechargeable lithium battery according to  claim 1 , wherein the element M is an element having higher boiling point than that of element X.  
     
     
         3 . A negative active material for a rechargeable lithium battery prepared by the method comprising: 
 alloying Si and element M by a mechanical alloying process to provide a SiM alloy where M is selected from the group consisting of Ni, Co, B, Cr, Cu, Fe, Mn, Ti, Y, and combinations thereof;    heating the SiM alloy at a first temperature;    adding element X as a powder to the heated SiM alloy, where X is selected from the group consisting of Ag, Cu, Au and combinations thereof, provided that if M is Cu, X is not Cu;    alloying the combined element X and SiM alloy by a mechanical alloying process to provide a SiMX alloy; and    heating the SiMX alloy at a second temperature lower than the first temperature.    
     
     
         4 . A rechargeable lithium battery comprising the negative active material for a rechargeable lithium battery as claimed in  claim 1 .  
     
     
         5 . 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;    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.    
     
     
         6 . The method according to  claim 5 , wherein the first heating is carried out at temperature between (Tm-100)° C. to (Tm-20)° C. where Tm is the melting point of the SiM alloy phase.