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,
 wherein the positive electrode active material comprises a composite oxide containing lithium and cobalt,   wherein the positive electrode active material comprises a crystal defect observed from a TEM image, and   wherein the positive electrode active material comprises a representative element in the crystal defect or in a vicinity of the crystal defect.   
     
     
         2 . A lithium-ion secondary battery comprising a positive electrode active material,
 wherein the positive electrode active material comprises a composite oxide containing lithium and cobalt,   wherein the positive electrode active material comprises a crystal defect observed from a TEM image, and   wherein the positive electrode active material comprises a representative element in a superficial portion of the positive electrode active material and a representative element in the crystal defect or in a vicinity of the crystal defect.   
     
     
         3 . A lithium-ion secondary battery comprising a positive electrode active material,
 wherein the positive electrode active material comprises a composite oxide containing lithium and cobalt,   wherein the positive electrode active material comprises a grain boundary observed from a TEM image, and   wherein the positive electrode active material comprises a representative element in the grain boundary or in a vicinity of the grain boundary.   
     
     
         4 . A lithium-ion secondary battery comprising a positive electrode active material,
 wherein the positive electrode active material comprises a composite oxide containing lithium and cobalt,   wherein the positive electrode active material comprises a grain boundary observed from a TEM image, and   wherein the positive electrode active material comprises a representative element in a superficial portion of the positive electrode active material and a representative element in the grain boundary or in a vicinity of the grain boundary.   
     
     
         5 . A lithium-ion secondary battery comprising a positive electrode active material,
 wherein the positive electrode active material comprises a composite oxide containing lithium and cobalt,   wherein the positive electrode active material comprises a crack portion observed from a TEM image, and   wherein the positive electrode active material comprises a representative element in the crack portion or in a vicinity of the crack portion.   
     
     
         6 . A lithium-ion secondary battery comprising a positive electrode active material,
 wherein the positive electrode active material comprises a composite oxide containing lithium and cobalt,   wherein the positive electrode active material comprises a crack portion observed from a TEM image, and   wherein the positive electrode active material comprises a representative element in a superficial portion of the positive electrode active material and a representative element in the crack portion or in a vicinity of the crack portion.   
     
     
         7 . The lithium-ion secondary battery according to  claim 1 ,
 wherein the representative element is magnesium.   
     
     
         8 . The lithium-ion secondary battery according to  claim 2 ,
 wherein the representative element is magnesium.   
     
     
         9 . The lithium-ion secondary battery according to  claim 3 ,
 wherein the representative element is magnesium.   
     
     
         10 . The lithium-ion secondary battery according to  claim 4 ,
 wherein the representative element is magnesium.   
     
     
         11 . The lithium-ion secondary battery according to  claim 5 ,
 wherein the representative element is magnesium.   
     
     
         12 . The lithium-ion secondary battery according to  claim 6 ,
 wherein the representative element is magnesium.   
     
     
         13 . The lithium-ion secondary battery according to  claim 11 ,
 wherein an atomic ratio of magnesium to cobalt in the crack portion or in the vicinity of the crack portion measured by a TEM-EDX point analysis is between 0 and 0.22.   
     
     
         14 . The lithium-ion secondary battery according to  claim 12 ,
 wherein an atomic ratio of magnesium to cobalt in the crack portion or in the vicinity of the crack portion measured by a TEM-EDX point analysis is between 0 and 0.22.   
     
     
         15 . The lithium-ion secondary battery according to  claim 1 ,
 wherein the positive electrode active material comprises titanium in the crystal defect or in the vicinity of the crystal defect.   
     
     
         16 . The lithium-ion secondary battery according to  claim 2 ,
 wherein the positive electrode active material comprises titanium in the crystal defect or in the vicinity of the crystal defect.   
     
     
         17 . The lithium-ion secondary battery according to  claim 3 ,
 wherein the positive electrode active material comprises titanium in the grain boundary or in the vicinity of the grain boundary.   
     
     
         18 . The lithium-ion secondary battery according to  claim 4 ,
 wherein the positive electrode active material comprises titanium in the grain boundary or in the vicinity of the grain boundary.   
     
     
         19 . The lithium-ion secondary battery according to  claim 5 ,
 wherein the positive electrode active material comprises titanium in the crack portion or in the vicinity of the crack portion.   
     
     
         20 . The lithium-ion secondary battery according to  claim 6 ,
 wherein the positive electrode active material comprises titanium in the crack portion or in the vicinity of the crack portion.   
     
     
         21 . The lithium-ion secondary battery according to  claim 19 ,
 wherein an atomic ratio of titanium to cobalt in the crack portion or in the vicinity of the crack portion measured by a TEM-EDX point analysis is greater than or equal to 0.05.   
     
     
         22 . The lithium-ion secondary battery according to  claim 20 ,
 wherein an atomic ratio of titanium to cobalt in the crack portion or in the vicinity of the crack portion measured by a TEM-EDX point analysis is greater than or equal to 0.05.   
     
     
         23 . The lithium-ion secondary battery according to  claim 2 ,
 wherein a relative value of a concentration of the representative element is greater than or equal to 0.4 and less than or equal to 1.5 when a surface of the positive electrode active material is subjected to an XPS analysis and a concentration of cobalt is defined as 1.   
     
     
         24 . The lithium-ion secondary battery according to  claim 4 ,
 wherein a relative value of a concentration of the representative element is greater than or equal to 0.4 and less than or equal to 1.5 when a surface of the positive electrode active material is subjected to an XPS analysis and a concentration of cobalt is defined as 1.   
     
     
         25 . The lithium-ion secondary battery according to  claim 6 ,
 wherein a relative value of a concentration of the representative element is greater than or equal to 0.4 and less than or equal to 1.5 when a surface of the positive electrode active material is subjected to an XPS analysis and a concentration of cobalt is defined as 1.   
     
     
         26 . The lithium-ion secondary battery according to  claim 16 ,
 wherein a relative value of a concentration of titanium is greater than or equal to 0.05 and less than or equal to 0.4 when a surface of the positive electrode active material is subjected to an XPS analysis and a concentration of cobalt is defined as 1.   
     
     
         27 . The lithium-ion secondary battery according to  claim 18 ,
 wherein a relative value of a concentration of titanium is greater than or equal to 0.05 and less than or equal to 0.4 when a surface of the positive electrode active material is subjected to an XPS analysis and a concentration of cobalt is defined as 1.   
     
     
         28 . The lithium-ion secondary battery according to  claim 20 ,
 wherein a relative value of a concentration of titanium is greater than or equal to 0.05 and less than or equal to 0.4 when a surface of the positive electrode active material is subjected to an XPS analysis and a concentration of cobalt is defined as 1.   
     
     
         29 . The lithium-ion secondary battery according to  claim 1 ,
 wherein the positive electrode active material comprises fluorine in the crystal defect or in the vicinity of the crystal defect.   
     
     
         30 . The lithium-ion secondary battery according to  claim 2 ,
 wherein the positive electrode active material comprises fluorine in the crystal defect or in the vicinity of the crystal defect.   
     
     
         31 . The lithium-ion secondary battery according to  claim 3 ,
 wherein the positive electrode active material comprises fluorine in the grain boundary or in the vicinity of the grain boundary.   
     
     
         32 . The lithium-ion secondary battery according to  claim 4 ,
 wherein the positive electrode active material comprises fluorine in the grain boundary or in the vicinity of the grain boundary.   
     
     
         33 . The lithium-ion secondary battery according to  claim 5 ,
 wherein the positive electrode active material comprises fluorine in the crack portion or in the vicinity of the crack portion.   
     
     
         34 . The lithium-ion secondary battery according to  claim 6 ,
 wherein the positive electrode active material comprises fluorine in the crack portion or in the vicinity of the crack portion.   
     
     
         35 . The lithium-ion secondary battery according to  claim 1 ,
 wherein the positive electrode active material comprises titanium in a superficial portion of the positive electrode active material.   
     
     
         36 . The lithium-ion secondary battery according to  claim 2 ,
 wherein the positive electrode active material comprises titanium in the superficial portion of the positive electrode active material.   
     
     
         37 . The lithium-ion secondary battery according to  claim 3 ,
 wherein the positive electrode active material comprises titanium in a superficial portion of the positive electrode active material.   
     
     
         38 . The lithium-ion secondary battery according to  claim 4 ,
 wherein the positive electrode active material comprises titanium in the superficial portion of the positive electrode active material.   
     
     
         39 . The lithium-ion secondary battery according to  claim 5 ,
 wherein the positive electrode active material comprises titanium in a superficial portion of the positive electrode active material.   
     
     
         40 . The lithium-ion secondary battery according to  claim 6 ,
 wherein the positive electrode active material comprises titanium in the superficial portion of the positive electrode active material.   
     
     
         41 . The lithium-ion secondary battery according to  claim 35 ,
 wherein an atomic ratio of titanium to cobalt in the superficial portion of the positive electrode active material measured by a TEM-EDX point analysis is between 0.10 and 0.18.   
     
     
         42 . The lithium-ion secondary battery according to  claim 36 ,
 wherein an atomic ratio of titanium to cobalt in the superficial portion of the positive electrode active material measured by a TEM-EDX point analysis is between 0.10 and 0.18.   
     
     
         43 . The lithium-ion secondary battery according to  claim 37 ,
 wherein an atomic ratio of titanium to cobalt in the superficial portion of the positive electrode active material measured by a TEM-EDX point analysis is between 0.10 and 0.18.   
     
     
         44 . The lithium-ion secondary battery according to  claim 38 ,
 wherein an atomic ratio of titanium to cobalt in the superficial portion of the positive electrode active material measured by a TEM-EDX point analysis is between 0.10 and 0.18.   
     
     
         45 . The lithium-ion secondary battery according to  claim 39 ,
 wherein an atomic ratio of titanium to cobalt in the superficial portion of the positive electrode active material measured by a TEM-EDX point analysis is between 0.10 and 0.18.   
     
     
         46 . The lithium-ion secondary battery according to  claim 40 ,
 wherein an atomic ratio of titanium to cobalt in the superficial portion of the positive electrode active material measured by a TEM-EDX point analysis is between 0.10 and 0.18.   
     
     
         47 . The lithium-ion secondary battery according to  claim 1 ,
 wherein a positive electrode active material layer comprises the positive electrode active material and a conductive additive, and   wherein the conductive additive comprises carbon fiber.   
     
     
         48 . The lithium-ion secondary battery according to  claim 2 ,
 wherein a positive electrode active material layer comprises the positive electrode active material and a conductive additive, and   wherein the conductive additive comprises carbon fiber.   
     
     
         49 . The lithium-ion secondary battery according to  claim 3 ,
 wherein a positive electrode active material layer comprises the positive electrode active material and a conductive additive, and   wherein the conductive additive comprises carbon fiber.   
     
     
         50 . The lithium-ion secondary battery according to  claim 4 ,
 wherein a positive electrode active material layer comprises the positive electrode active material and a conductive additive, and   wherein the conductive additive comprises carbon fiber.   
     
     
         51 . The lithium-ion secondary battery according to  claim 5 ,
 wherein a positive electrode active material layer comprises the positive electrode active material and a conductive additive, and   wherein the conductive additive comprises carbon fiber.   
     
     
         52 . The lithium-ion secondary battery according to  claim 6 ,
 wherein a positive electrode active material layer comprises the positive electrode active material and a conductive additive, and   wherein the conductive additive comprises carbon fiber.   
     
     
         53 . The lithium-ion secondary battery according to  claim 47 ,
 wherein the carbon fiber comprises carbon nanofiber or carbon nanotube.   
     
     
         54 . The lithium-ion secondary battery according to  claim 48 ,
 wherein the carbon fiber comprises carbon nanofiber or carbon nanotube.   
     
     
         55 . The lithium-ion secondary battery according to  claim 49 ,
 wherein the carbon fiber comprises carbon nanofiber or carbon nanotube.   
     
     
         56 . The lithium-ion secondary battery according to  claim 50 ,
 wherein the carbon fiber comprises carbon nanofiber or carbon nanotube.   
     
     
         57 . The lithium-ion secondary battery according to  claim 51 ,
 wherein the carbon fiber comprises carbon nanofiber or carbon nanotube.   
     
     
         58 . The lithium-ion secondary battery according to  claim 52 ,
 wherein the carbon fiber comprises carbon nanofiber or carbon nanotube.