The core-shell structure of Co3O4@Li2MnO3 was prepared by a facile hydrothermal method following heat treatment at 300 [degree]C. The outer shell is porous and makes the diffusion of Li+ ions to the inner shell easier. The synergetic effect between the core and shell shows that the Co3O4 shell in the composite serves as a host to react with lithium oxide removed from the Li2MnO3 core during the initial charging process, which eliminates the huge irreversible capacity loss of Li2MnO3. As the cathode material for lithium ion batteries, the composite exhibits an attractive discharge capacity of 178 mA h g-1 with little irreversible capacity loss in the voltage range of 2.0-4.8 V. Its cycling performance is stable without any drastic capacity fading when cycling in the high voltage range of 2.0-4.6 V.