A series of lithium-rich cathode materials, xLi(2)MnO(3)center dot(1-x)LiNi0.5Mn0.5O2 (x=0.1-0.8), were successfully synthesized by a sol-gel method. X-ray diffraction, scanning electron microscopy, and electrochemical tests were used to investigate the crystal structure, morphology, and electrochemical performance of the as-synthesized materials, respectively. The results showed that the materials with higher Li2MnO3 content had higher initial discharge capacity but poorer cycle stability, while the materials with lower Li2MnO3 content showed lower discharge capacity but better cycle stability, and the spinel impurity phase was also found. Based on the data, the optimal electrochemical properties were obtained when x=0.5 in xLi(2)MnO(3)center dot (1-x)LiNi0.5Mn0.5O2. Moreover, the electrochemical properties were also worthy of attention when x=0.4, 0.6.