Positive Electrode Active Material, Method for Manufacturing Positive Electrode Active Material, and Secondary Battery

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 comprising a positive electrode active material and a conductive additive,   wherein the positive electrode active material comprises a composite oxide containing lithium, nickel, cobalt, and manganese,   wherein the conductive additive comprises a region where the conductive additive is formed in such a way as to coat a superficial portion of the positive electrode active material,   wherein the conductive additive comprises carbon fiber, graphene, or multilayer graphene, and   wherein the superficial portion of the positive electrode active material comprises fluorine.   
     
     
         2 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material and a conductive additive,   wherein the positive electrode active material comprises a composite oxide containing lithium, nickel, cobalt, and manganese,   wherein the conductive additive comprises a region where the conductive additive is formed in such a way as to adhere to a superficial portion of the positive electrode active material,   wherein the conductive additive comprises carbon fiber, graphene or multilayer graphene, and   wherein the superficial portion of the positive electrode active material comprises fluorine.   
     
     
         3 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material layer,   wherein the a positive electrode active material layer comprises a positive electrode active material and a conductive additive,   wherein the positive electrode active material comprises a composite oxide containing lithium, nickel, cobalt, and manganese,   wherein a superficial portion of the positive electrode active material comprises fluorine,   wherein the positive electrode active material comprises a first surface and a second surface facing in different directions in a cross-sectional view,   wherein the conductive additive comprises a first region making surface contact with the first surface of the positive electrode active material in the cross-sectional view,   wherein the conductive additive comprises a second region making surface contact with the second surface of the positive electrode active material in the cross-sectional view, and   wherein the conductive additive comprises carbon fiber, graphene or multilayer graphene.   
     
     
         4 . A lithium-ion secondary battery comprising:
 a positive electrode comprising a positive electrode active material layer,   wherein the a positive electrode active material layer comprises a positive electrode active material and a conductive additive,   wherein the positive electrode active material comprises a composite oxide containing lithium, nickel, cobalt, and manganese,   wherein a superficial portion of the positive electrode active material comprises fluorine,   wherein the conductive additive comprises a first surface and a second surface facing in different directions in a cross-sectional view,   wherein the positive electrode active material comprises a first region making surface contact with the first surface of the conductive additive in the cross-sectional view,   wherein the positive electrode active material comprises a second region making surface contact with the second surface of the conductive additive in the cross-sectional view, and   wherein the conductive additive comprises carbon fiber, graphene, or multilayer graphene.   
     
     
         5 . The lithium-ion secondary battery according to  claim 1 , wherein the carbon fiber is carbon nanofiber or carbon nanotube. 
     
     
         6 . The lithium-ion secondary battery according to  claim 2 , wherein the carbon fiber is carbon nanofiber or carbon nanotube. 
     
     
         7 . The lithium-ion secondary battery according to  claim 3 , wherein the carbon fiber is carbon nanofiber or carbon nanotube. 
     
     
         8 . The lithium-ion secondary battery according to  claim 4 , wherein the carbon fiber is carbon nanofiber or carbon nanotube.