Comportement electrochimique des phases NaxCoO2

Electrochemical intercalation or desintercalation of sodium in layered NaxCoO2 oxides has been carried out. Previous studies had shown the existence of four phases in the composition rang 0.5 ⩽ x ⩽ 1, whose structures differ by the sequence of the (CoO2)n sheets along the hexagonal c axis. These materials have been used as cathodes in sodium batteries. The charge or discharge potentials (2.0 V ⩽ V ⩽ 3.5 V) have been measured as a function of x. During the electrochemical reactions reversible structural changes occur only when the involved structures differ by a small sheet shift.