Structure and electronic structure evolution of P2-NaxCoO2 phases from X-ray diffraction and 23Na magic angle spinning nuclear magnetic resonance

P2-Na 0.70 CoO 2 is considered as a model material for positive electrode application in Na-ion batteries. In this paper, we report an in-depth study and characterization of P2-Na x CoO 2 system, in order to understand the material evolution from the point of view of structure at different scales and electronic properties upon charge up to high voltage (4.6 V). Using a combination of ex-situ and operando XRD and ex situ 23 Na MAS NMR we discuss the structural changes occurring due to the deintercalation of Na + ions from the interlayer slabs and the change in the electronic structure and magnetic properties. The XRD study allows discussing the general evolution in relation with previous works. The novelty lies here in the observation for the first time of an ordered phase for x=1/3 appearing between above 4.3 V followed by a disordering in the slabs stacking for higher voltages. The combination of the data obtained by the different techniques allowed the interpretation of the NMR shift and shape evolution versus the Na content. This study reveals a complex behavior due to the presence of localized and delocalized electrons whose relative proportions is changing versus Na content