A polytype of LiCoO2 has been synthesized through an ion-exchange reaction. By exchanging Na+ for Li+ ions from an OP4-(Li/Na)CoO2-mixed cobaltite, a LiCoO2 stacking is obtained. It alternatively combines O2-and O3-LiCoO2 polytypes and corresponds to an O4 stacking. The phase crystallizes in the hexagonal system with cell parameters a(hex)=2.802(1) A degrees and c(hex)=18.89(2) A degrees. As the O2 phase, the O4-LiCoO2, is metastable; it transforms into the thermodynamically stable O3-LiCoO2 at around 350-400 degrees C. The crystallographic data, the thermal properties, and the electrochemical behavior of this phase are presented.