On the mechanism of the P2–Na 0.70CoO 2→O2–LiCoO 2 exchange reaction—Part I: proposition of a model to describe the P2–O2 transition

Abstract

A model was proposed to describe the exchange reaction of sodium by lithium in P2 crystals. The exchange consists on the formation of nucleation centers and then on the growth of O2 domains in P2 crystals from these nucleation centers. Octahedral environments for lithium ions are obtained when one slab over two glides by (2/3,1/3,0) or by (1/3,2/3,0) in P2 structure. The existence of two different gliding vectors should lead to stacking faulted structures that can be simulated using DIFFaX software. The comparison of simulated and experimental XRD patterns for O2–LiCoO 2 (ex-Na 0.7CoO 2) has shown that in that case the growth of the O2 domains in the P2 crystals is faster than the formation of nucleation centers.