Positive electrode active material including lithium cobaltate coated with lithium titanate and magnesium oxide

Abstract

A positive electrode active material which can improve cycle characteristics of a secondary battery is provided. Two kinds of regions are provided in a superficial portion of a positive electrode active material such as lithium cobaltate which has a layered rock-salt crystal structure. The inner region is a non-stoichiometric compound containing a transition metal such as titanium, and the outer region is a compound of representative elements such as magnesium oxide. The two kinds of regions each have a rock-salt crystal structure. The inner layered rock-salt crystal structure and the two kinds of regions in the superficial portion are topotaxy; thus, a change of the crystal structure of the positive electrode active material generated by charging and discharging can be effectively suppressed. In addition, since the outer coating layer in contact with an electrolyte solution is the compound of representative elements which is chemically stable, the secondary battery having excellent cycle characteristics can be obtained.

1 . A lithium-ion secondary battery comprising:
 a positive electrode active material comprising a transition metal,   wherein the positive electrode active material is configured to diffuse lithium in a region from a depth of 0.5 nm to a depth of 50 nm from a surface of the positive electrode active material, and   wherein the positive electrode active material is configured to suppress dissolution of the transition metal from the positive electrode active material.   
     
     
         2 . The lithium-ion secondary battery according to  claim 1 ,
 wherein the positive electrode active material is configured to suppress release of oxygen from the positive electrode active material.   
     
     
         3 . A lithium-ion secondary battery comprising:
 a positive electrode active material comprising lithium, cobalt, and oxygen,   wherein the positive electrode active material is configured to diffuse lithium in a region from a depth of 0.5 nm to a depth of 50 nm from a surface of the positive electrode active material, and   wherein the positive electrode active material is configured to suppress dissolution of cobalt from the positive electrode active material.   
     
     
         4 . The lithium-ion secondary battery according to  claim 3 ,
 wherein the positive electrode active material is configured to suppress release of oxygen from the positive electrode active material.   
     
     
         5 . A lithium-ion secondary battery comprising:
 a positive electrode active material comprising lithium cobaltate,   wherein the positive electrode active material is configured to diffuse lithium in a region from a depth of 0.5 nm to a depth of 50 nm from a surface of the positive electrode active material, and   wherein the positive electrode active material is configured to suppress dissolution of cobalt from the positive electrode active material.   
     
     
         6 . The lithium-ion secondary battery according to  claim 5 ,
 wherein the positive electrode active material is configured to suppress release of oxygen from the positive electrode active material.