Positive electrode active material for non-aqueous electrolyte secondary battery and method for producing same
This cathode active material for a secondary battery using a non-aqueous electrolyte includes nickel-rich lithium transition-metal oxide, exhibits a hard X-ray photoelectron spectroscopy (HAXPES) peak of 1,560 to 1,565 eV in binding energy from an Al-rich layer, using a photon energy of 6 KeV, and with respect to the mean particle diameter r of the lithium transition-metal oxide particle, the Al concentration is approximately constant within 0.35r of the center.
1. A positive electrode active material for a non-aqueous electrolyte secondary battery, including a nickel-containing lithium transition metal oxide represented by a formula (1), wherein
a peak of 1560 to 1565 eV in binding energy from an Al-rich layer exists in hard X-ray photoelectron spectroscopy (HAXPES) at a photon energy of 6 KeV, and when lithium transition metal oxide particles have an average particle diameter of r, an Al concentration is approximately constant within a range of 0.35r from the center:
Li x Ni a Co b Al c M d O 2 (Formula 1),
wherein x, a, b, c, and d meet 0.95<x<1.05, 0.91≤a<1, 0<b<0.15, 0≤d<0.15, and 0.03<c, and M represents at least one metal element selected from the group consisting of B, Si, Mg, Ge, Sn, Mg, Cr, Mn, Ti, Nb, Mo, and Fe,
wherein the Al-rich layer is a mixed body of LiAlO 2 and an oxide containing Li, Ni, Co, and Al,
wherein the Al-rich layer has a thickness of 100 nm or less,
wherein the Al concentration within the range of 0.35r from the center is 3 mol % or more, and
wherein the Al concentration of the lithium transition metal oxide particles meets 0.99<(Al concentration at 0.35r)/(Al concentration at central portion)<1.01.
2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the Al-rich layer contains LiAlO 2 .
3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein aluminum is dissolved to form a solid solution inside the lithium transition metal oxide particles.
4. A method for producing the positive electrode active material for a non-aqueous secondary battery of claim 1 , the positive electrode active material including the nickel-containing lithium transition metal oxide, the method including the steps of:
mixing a nickel cobalt aluminum-containing oxide carrying lithium hydroxide or lithium carbonate on a surface thereof with an Al compound; and
heating the nickel cobalt aluminum-containing oxide and the Al compound at 500° C. to 800° C.