Positive electrode active material for lithium ion secondary battery

Abstract

Disclosed is a positive electrode active material for a lithium ion secondary battery, including lithium-transition metal composite oxide of a layer crystal structure, in which the lithium-transition metal composite oxide contains an element that improves conductivity of electrons in the lithium-transition metal composite oxide. Use of this positive electrode active material can improve cycle characteristics, high rate characteristics and thermal stability of lithium ion secondary batteries. Furthermore, by use of this positive electrode active material, gas generation in batteries can be decreased.

1 . A positive electrode active material for a lithium ion secondary battery, including lithium-transition metal composite oxide of a layer crystal structure, 
 in which the lithium-transition metal composite oxide has a sulfate group at least on surfaces of particles of the lithium-transition metal composite oxide.    
     
     
         2 . The positive electrode active material for a lithium ion secondary battery according to  claim 1 , wherein a general formula of the lithium-transition metal composite oxide is  
         Li k M 1-n Z n O 2-p X r    
       wherein M represents Co and/or Ni; Z represents at least one element selected from the group consisting of transition metals other than the M and elements of Groups 2, 13 and 14 of the periodic table; x represents a halogen; k represents a number satisfying 0.95<k≦1.10; n represents a number satisfying 0≦n≦0.5; p represents a number satisfying 0≦p≦1; and r represents a number satisfying 0≦r≦2p.  
     
     
         3 . The positive electrode active material for a lithium ion secondary battery according to  claim 1 , wherein a general formula of the lithium-transition metal composite oxide is  
         Li y M 1   1-x M 2   x O z    
       wherein M 1  represents Co and/or Ni; M 2  represents at least one element selected from Al, Mg, Mn, Ti and Zr; x represents a number satisfying 0<x≦0.02; y represents a number satisfying 0.95≦y≦1.10; and z represents a number satisfying 1.8<z<2.2.  
     
     
         4 . The positive electrode active material for a lithium ion secondary batter according to  claim 1 , wherein a specific surface area of the lithium-transition metal composite oxide is 0.2 to 2.0 m 2 /g.  
     
     
         5 . The positive electrode active material for a lithium ion secondary battery according to  claim 1 , wherein a proportion of particles of the lithium-transition metal composite oxide having a volume based particle size of 1 μm or less is 10 vol % or less based on total particles.  
     
     
         6 . The positive electrode active material for a lithium ion secondary battery according to  claim 1 , wherein a proportion of sulfate groups present on surfaces of particles of the lithium-transition metal composite oxide is 0.01 mol % or more and 1 mol % or less with respect to the lithium-transition metal composite oxide.  
     
     
         7 . A lithium ion secondary battery comprising: the positive electrode active material for a lithium ion secondary battery according to  claim 1 , a negative electrode active material, an electrolytic solution and a separator.