Positive active material, lithium battery including the same, and method of manufacturing the positive active material

Abstract

A positive active material including a core including a compound capable of reversibly intercalating and deintercalating lithium and LiNaSO 4 that is coated on at least a part of a surface of the core or that blends with the core.

What is claimed is: 
     
         1 . A positive active material, comprising:
 a core including a compound capable of reversibly intercalating and deintercalating lithium; and   LiNaSO 4  that is coated on at least a part of a surface of the core or that blends with the core.   
     
     
         2 . The positive active material as claimed in  claim 1 , wherein the LiNaSO 4  is attached on the core in a layered form or an island form. 
     
     
         3 . The positive active material as claimed in  claim 1 , wherein:
 an amount of the core is in a range of about 95 wt % to about 99.5 wt % of a total weight of the core and the LiNaSO 4 , and an amount of the LiNaSO 4  is in a range of about 0.5 wt % to about 5 wt % of the total weight of the core and the LiNaSO 4 .   
     
     
         4 . The positive active material as claimed in  claim 1 , wherein:
 an amount of the core is in a range of about 97 wt % to about 99.3 wt % of a total weight of the core and the LiNaSO 4 , and an amount of the LiNaSO 4  is in a range of about 0.7 wt % to about 3 wt % of the total weight of the core and the LiNaSO 4 .   
     
     
         5 . The positive active material as claimed in  claim 1 , wherein the core includes at least one selected from compounds represented by Formulae 1 to 3:
   Li a (Ni x M′ y )O 2    [Formula 1]
   wherein, in Formula 1,   M′ is at least one element selected from Co, Mn, Fe, V, Cu, Cr, Al, Mg, and Ti; and   0.9<a≦1.1, 0≦x<0.4, 0.6≦y≦1, and x+y=1,
   LiMPO 4    [Formula 2]
 
   wherein, in Formula  2 ,   M is at least one element selected from Fe, Mn, Ni, Co, and V,
   Li 1+y Mn 2−y−z M z O 4−x Q x    [Formula 3]
 
   wherein, in Formula 3,   M is at least one element selected from Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr, and Zn;   Q is at least one element selected from N. F, S, and Cl; and   0≦x≦1, 0≦y≦0.34, and 0≦z≦1.   
     
     
         6 . The positive active material as claimed in  claim 5 , wherein:
 the core includes the compound represented by Formula  1 , and   the compound represented by Formula 1 is further substituted or doped with at least one element selected from Ca, Mg, Al, Ti, Sr, Fe, Co, Cu, Zn, Y, Zr, Nb, and B, wherein the substituted or doped element is different from Ni and M′.   
     
     
         7 . A lithium battery, comprising:
 a positive electrode including the positive active material as claimed in  claim 1 ;   a negative electrode facing the positive electrode; and   an electrolyte between the positive electrode and the negative electrode.   
     
     
         8 . The lithium battery as claimed in  claim 7 , wherein the lithium battery operates within a voltage range of about 4.3 V to about 4.6 V. 
     
     
         9 . A method of manufacturing a positive active material, the method comprising:
 preparing a compound capable of reversibly intercalating and deintercalating lithium;   adding and mixing a sodium source and a sulfate source to the compound to obtain a powder mixture; and   heat-treating the powder mixture to obtain a positive active material including LiNaSO 4  that is coated on at least a part of a surface of the compound capable of reversibly intercalating and deintercalating lithium or that blends with the compound capable of reversibly intercalating and deintercalating lithium.   
     
     
         10 . The method as claimed in  claim 9 , wherein the sodium source includes at least one selected from sodium dodecyl sulfate (CH 3 (CH 2 ) 11 SO 4 Na), sodium sulfate (Na 2 SO 4 ), sodium nitrate (NaNO 3 ), sodium acetate (CH 3 COONa), sodium carbonate (Na 2 CO 3 ), sodium bicarbonate (NaHCO 3 ), and sodium hydroxide (NaOH). 
     
     
         11 . The method as claimed in  claim 9 , wherein the sulfate source includes at least one selected from sodium dodecyl sulfate (CH 3 (CH 2 ) 11 SO 4 Na), sodium sulfate (Na 2 SO 4 ), sulfuric acid (H 2 SO 4 ), ammonium sulfate ((NH 4 ) 2 SO 4 ), and lithium sulfate (Li 2 SO 4 ). 
     
     
         12 . The method as claimed in  claim 9 , wherein the heat-treating is performed at a temperature in a range of about 600° C. to about 1,000° C. 
     
     
         13 . The method as claimed in  claim 9 , wherein:
 an amount of the compound capable of intercalating and deintercalating lithium is in a range of about 95 wt % to about 99.5 wt % of a total weight of the compound capable of intercalating and deintercalating lithium and the LiNaSO 4 , and   an amount of the LiNaSO 4  is in a range of about 0.5 wt % to about 5 wt % of the total weight of the compound capable of intercalating and deintercalating lithium and the LiNaSO 4 .