Synthesis and investigations on an O4-LiCoO₂ polytype

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 ahex = 2.802(1) Å and chex = 18.89(2) Å. As the O2 phase, the O4-LiCoO2, is metastable; it transforms into the thermodynamically stable O3-LiCoO2at around 350–400°C. The crystallographic data, the thermal properties, and the electrochemical behavior of this phase are presented