Cathode active material for lithium secondary battery

Abstract

Disclosed herein is a cathode active material based on lithium nickel-manganese-cobalt oxide represented by Formula 1, wherein the lithium nickel-manganese-cobalt oxide has a nickel content of at least 40% among overall transition metals and is coated with a conductive polymer at a surface thereof. A lithium secondary battery having the disclosed cathode active material has advantages of not deteriorating electrical conductivity while enhancing high temperature stability, so as to efficiently provide high charge capacity.

1 . A cathode active material, comprising:
 a lithium nickel-manganese-cobalt oxide represented by Formula 1, wherein the lithium nickel-manganese-cobalt oxide has a nickel content of at least 40% among overall transition metals and is coated with a conductive polymer at a surface thereof:
   Li x M y O 2    (1)
 
   wherein M is Ni 1-a-b Mn a Co b  (0.05≦a≦0.4, 0.1≦b≦0.4, (1-a-b)≦0.9), x+y is about 2 and 0.95≦x≦1.15.   
     
     
         2 . The cathode active material according to  claim 1 , wherein the lithium nickel-manganese-cobalt oxide comprises particles with an agglomerated structure consisting of an aggregate of microfine particles. 
     
     
         3 . The cathode active material according to  claim 1 , wherein the lithium nickel-manganese-cobalt oxide has an average particle diameter D50 of 3 to 20 μm. 
     
     
         4 . The cathode active material according to  claim 2 , wherein the lithium nickel-manganese-cobalt oxide comprises an aggregate of microfine particles having an average particle diameter D90 of 0.01 to 8 μm. 
     
     
         5 . The cathode active material according to  claim 1 , wherein the conductive polymer is at least one selected from a group consisting of polyacetylene, polyphenylene, polyaniline, polythiophene, polyphenylene-vinylene, polyvinylene, polyaminopyridine and polypyrrole. 
     
     
         6 . The cathode active material according to  claim 1 , wherein the conductive polymer has a melting point of 80 to 300° C. 
     
     
         7 . The cathode active material according to  claim 1 , wherein a coating amount ranges from 0.5 to 10% by weight relative to a total weight of the active material. 
     
     
         8 . The cathode active material according to  claim 1 , wherein the coating thickness of the conductive polymer range from 0.1 to 10 μm. 
     
     
         9 . A lithium secondary battery including the cathode active material as set forth in  claim 1 . 
     
     
         10 . The lithium secondary battery according to  claim 9 , wherein the lithium secondary battery is used as a power supply for a power tool, an electric vehicle, an electric two-wheel vehicle and/or an electric golf cart.