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