Lithium nickel-manganese-cobalt oxide positive electrode active material
A nonaqueous electrolytic secondary cell produced at low cost and having a large capacity comprises a negative electrode having an active material mainly composed of a material that at least absorbs and releases lithium ions or metallic lithium, a positive electrode, and an electrolyte. The active material of the positive electrode is an oxide containing nickel, manganese, and cobalt, and the contents of the elements are substantial the same.
1. A positive electrode active material comprising crystal particles of a lithium transition metal oxide,
said lithium transition metal oxide containing three different transition metal elements in equal amounts and having a layered crystal structure,
wherein said layered crystal structure of said oxide is an R3m layered structure,
said three different transition metal elements are nickel, cobalt, and manganese,
the arrangement of oxygen atoms constituting said oxide is a cubic close-packed structure,
said three transition metal elements constitute a superlattice of [√3×√3] R30°, and
said three transition metal elements are regularly arranged in the 3(a) site of the R3m layered structure.
2. The positive electrode active material in accordance with claim 1 , comprising a mixture of said crystal particles of said oxide with a particle size of 0.1 to 2 μm and secondary particles with a particle size of 2 to 20 μm.
3. The positive electrode active material in accordance with claim 1 , wherein the volume of a unit lattice of said crystal particles does not increase upon oxidation.
4. A positive electrode active material comprising crystal particles of a lithium transition metal oxide,
said lithium transition metal oxide containing three different transition metal elements in equal amounts and having a layered crystal structure,
wherein the three transition metal elements constitute a superlattice of [√3×√3] R30°,
the surface of said crystal particles is doped with at least one element different from said three different transition elements,
wherein said layered crystal structure of said oxide is an R3m layered structure,
said three different transition metal elements are nickel, cobalt, and manganese,
the arrangement of oxygen atoms constituting said oxide is a cubic close-packed structure,
said three transition metal elements are regularly arranged in the 3(a) site of the R3m layered structure in said crystal particles except said surface doped with said at least one different element,
said at least one different element is selected from the group consisting of aluminum, magnesium, calcium, strontium, yttrium, and ytterbium, and
the amount of said at least one different element is 0.05 to 20 atom % of the total amount of said three different transition metal elements.