Lithium nickel manganese-containing composite oxide, method for preparation thereof, positive electrode plate, secondary battery and electrical device

A preparation method of a lithium nickel manganese-containing composite oxide comprising the following steps:

• S1:
• providing a raw material obtained by mixing a source of element Li, a source of element Ni, a source of element Mn, a source of element A, and an optional source of element M in a predetermined proportion;
• S2:
• heating the raw material obtained in S1 to a first temperature T1 under an oxygen-containing atmosphere, maintaining at the first temperature T1 for a first time t1, cooling to room temperature, after which a intermediate product is obtained, 850° C.≤T1≤1100° C.;
• and
• S3:
• heating the intermediate product obtained in S2 to a second temperature T2 under an oxygen-containing atmosphere, maintaining at the second temperature T2 for a second time t2, after which a lithium nickel manganese-containing composite oxide is obtained, 0° C. ≤T1−T2≤200° C., and T2≥800° C., wherein the lithium nickel manganese-containing composite oxide is a particle with a monocrystal morphology or quasi-monocrystal morphology, the lithium nickel manganese-containing composite oxide has a spherical or spherical-like grain shape, and the lithium nickel manganese-containing composite oxide has a general formula of Li1+xNi0.5+yMzMn1.5−x−y−z−aAaO4−k, −0.2≤x≤0.5, −0.2≤y≤0.2, 0≤z≤0.2, 0<a≤0.2, 0≤k≤0.2, A comprises one or more selected from Si, P and S, M comprises one or more selected from a metal-doping element.