In-situ analysis of NaMNb(PO4)3 M = Fe, Al anode for sodium ion batteries: follow-up of the structural evolution and electrode reaction

We propose the in-situ XRD study of the NASICON (NA Super Ionic CONductors) samples NaFeNb(PO4)3 and NaAlNb(PO4)3 considered as anodes for sodium ion batteries. Our electrochemical tests reveal good performances, but two main aspects are still undetermined: i) while the two compounds are isostructural, the electrochemical behavior is significantly different in terms of capacity and charge/discharge profiles; ii) the electrochemically active species, unexpectedly is Nb. For these reasons, we aim to perform in situ XRD study to follow up the structural evolution of the systems, identify the Na ions site and occupancy, and determine the electrode reaction. The XRD data obtained from the optical cell will be analyzed according to the Rietveld method (determining the structure), with MEM and Frourier map methods (locating the Na ion sites). Data will be coupled with ex situ SEM/TEM analysis, XPS, and possibly with XAS data and neutron diffraction data (proposals under evaluation).