Positive electrode active material for a rechargeable lithium-ion battery

A positive electrode active material suitable for lithium-ion rechargeable batteries, said positive electrode active material comprising Li, M′, and oxygen, wherein M′ comprises:

• Ni in a content x, wherein 70.0 mol %≤x≤75.0 mol %, relative to M′;
• Co in a content y, wherein 0.1 mol %≤y≤40.0 mol %, relative to M′;
• Mn in a content z, wherein 0.1 mol %≤z≤70.0 mol %, relative to M′,
• D in a content a, wherein 0.0 mol %≤a≤2.0 mol %, relative to M′, wherein D comprises at least one element of the group consisting of:
• Al, B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W, Zn, and Zr, and
• wherein x, y, z, and a contents are measured by ICP, and x+y+z+a is 100.0 mol %,
• wherein said positive electrode active material comprises secondary particles comprising a plurality of primary particles, and
• wherein the positive electrode active material has a Ni content Niedge and Co content Coedge as measured by cross-sectional EDS (CS-EDS) at an edge of the secondary particle of the positive electrode active material, wherein Niedge and Coedge contents are expressed as molar fractions compared to the sum of Ni, Mn, and Co content as measured by CS-EDS at the edge of the secondary particle of the positive electrode active material,
• wherein the positive electrode active material has a Ni content Nicenter and Co content Cocenter measured by CS-EDS at the center of the secondary particle of the positive electrode active material, wherein Nicenter and Cocenter contents are expressed as molar fractions compared to the sum of Ni, Mn, and Co content as measured by CS-EDS at the center of the secondary particle of the positive electrode active material,
• wherein the ratio Niedge/Nicenter<1.0
• wherein the ratio Coedge/Cocenter>1.0
• wherein said secondary particles have an average crystallite size of at most 65 nm, as determined by XRD.