Li-rich layered oxide is one of the most promising cathode materials for high-energy-density Li-ion batteries (LIBs). The composition, structure and morphology of precursors have significant influence on the electrochemical performance of the final cathode material. The capacity and initial coulombic efficiency of Li1.2Mn0.54Ni0.13Co0.13O2 can be simultaneously improved by sintering a nanoplate precursor with Li2CO3 in our previous work. Herein, the morphology and the formation mechanism of such nanoplate are investigated through a designed orthogonal tests. The optimal concentration of transition metal ions, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and polyvinyl pyrrolidone (PVP) are 0.1, 0.031 and 0.004gmL−1, respectively. The as-prepared Li1.2Mn0.54Ni0.13Co0.13O2 from optimal nanoplate demonstrate an improved discharge capacity (323.8mAhg−1 at 20mAg−1), initial coulombic efficiency (81.3%), and rate capability (195.8mAhg−1 at 3C). This new precursor architecture opens a promising avenue for the development of high-performances cathode materials of LIBs.