The layered rocksalt-type oxide, Li2PtO3, is the first full 4 V class cathode material among 5d metal compounds. We investigated the electrochemical, structural and kinetic characteristics of the 4 V region. The volumetric capacity of the 4 V plateau on discharge was comparable to that of LiCoO2. Moreover, the volume change during cycling was less then that of LiCoO2. We measured the total conductivity and Li diffusivity in Li2PtO3 by the ac impedance and current-pulse relaxation techniques, respectively.