Positive active material for lithium secondary battery and method of manufacturing same

Abstract

A positive active material for a lithium secondary battery comprises a core comprising a compound that can reversibly intercalate and deintercalate lithium; and a compound attached to the surface of the core and represented by Chemical Formula 1: Li 1+x M(I) x M(II) 2−x Si y P 3−y O 12 ,  [Chemical Formula 1] wherein M(I) and M(II) are selected from the group consisting of Al, Zr, Hf, Ti, Ge, Sn, Cr, Nb, Ga, Fe, Sc, In, Y, La, Lu, and Mg, and 0<x≦0.7, 0≦y≦1.

1 . A positive active material for a lithium secondary battery comprising:
 a core comprising a compound capable of reversibly intercalating and deintercalating lithium ions; and   a compound attached to a surface of the core and represented by Chemical Formula 1:
   Li 1+x M(I) x M(II) 2−x SI y P 3−y O 12   [Chemical Formula 1]
 
   wherein M(I) and M(II) are selected from the group consisting of Al, Zr, Hf, Ti, Ge, Sn, Cr, Nb, Ga, Fe, Sc, In, Y, La, Lu, and Mg, and 0<x≦0.7, 0≦y≦1.   
     
     
         2 . The positive active material of  claim 1 , wherein the M(I) is Al and the M(II) is Ti. 
     
     
         3 . The positive active material of  claim 1 , wherein the compound represented by Chemical Formula 1 is attached to the core as a layer and/or discrete particles. 
     
     
         4 . The positive active material of  claim 1 , wherein the compound represented by Chemical Formula 1 is Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 . 
     
     
         5 . The positive active material of  claim 1 , wherein the core comprises an amount of about 96 wt % to about 98.5 wt % of the positive active material, and the compound represented by Chemical Formula 1 comprises an amount of about 1.5 wt % to about 4 wt % of the positive active material. 
     
     
         6 . The positive active material of  claim 1 , wherein the core comprises at least one composite oxide of lithium and a metal selected from the group consisting of cobalt, manganese, nickel, and a combination thereof. 
     
     
         7 . A positive electrode comprising:
 the positive active material of  claim 1 ,   a conductive material, and   a binder.   
     
     
         8 . A lithium secondary battery comprising the positive electrode of  claim 7 . 
     
     
         9 . The lithium secondary battery of  claim 8 , wherein the lithium secondary battery is configured to operate at a charge cut-off voltage of 4.35V or higher. 
     
     
         10 . A method of manufacturing a positive active material for a lithium secondary battery comprising:
 mixing a Li source, a M(I) source, a M(II) source, and a phosphate source to prepare a mixture;   heating the mixture to prepare a compound represented by Chemical Formula 1:
   Li 1+x M(I) x M(II) 2−x Si y P 3−y O 12   [Chemical Formula 1]
 
   wherein M(I) and M(II) are selected from the group consisting of Al, Zr, Hf, Ti, Ge, Sn, Cr, Nb, Ga, Fe, Sc, In, Y, La, Lu, and Mg, and 0<x≦0.7, 0≦y≦1;   admixing a core comprising a material that reversibly intercalates and deintercalates lithium ions to the compound represented by Chemical Formula 1 to prepare a mixed product; and   heating the mixed product.   
     
     
         11 . The method of  claim 10 , wherein the heating the mixture comprises;
 heating the mixture to form a compound represented by the above Chemical Formula 1 in a first heating step;   pulverizing the compound obtained in the first heating step; and   heating the pulverized compound for crystallization in a second heating step,   wherein the first heating step is performed at a lower temperature than the second heating step.   
     
     
         12 . The method of  claim 11 , wherein the M(I) is Al and the M(II) is Ti. 
     
     
         13 . The method of  claim 11 , wherein the compound represented by Chemical Formula 1 is Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 . 
     
     
         14 . The method of  claim 11 , wherein the core comprises a composite oxide of a metal selected from the group consisting of cobalt, manganese, nickel, and a combination thereof, and lithium. 
     
     
         15 . A positive electrode for a lithium secondary battery comprising a positive active material prepared according to the method of  claim 10 , a conductive material, and a binder. 
     
     
         16 . A lithium secondary battery comprising the positive electrode of  claim 15 . 
     
     
         17 . The lithium secondary battery of  claim 16 , configured to operate at a charge cut-off voltage of 4.35V or higher.