Li-rich Mn-based Li1+x (Mn0.533Ni0.233Co0.233)1−x O2 (x =0, 0.045, 0.09, 0.135, 0.18, 0.225) materials have been prepared by a conventional solid-state reaction. XRD, SEM and half-cell tests are investigated on the influence of Li content. Pure phase can be obtained when Li-excessive value x keeps between 0.045 and 0.18. The initial efficiency (Q 1d/Q 1c) almost keeps the same level of 70% for different Li-excessive samples. Li1.045Mn0.509Ni0.223Co0.223O2 sample shows highest discharge capacity of 259.8mAhg−1. Li1.09Mn0.486Ni0.212Co0.212O2 sample exhibits the best rate capability, and almost no reduction is observed after 24-time cycles in different discharge current density.