Alluaudite-Na1.47 Fe3(PO4)3 : Structural and electrochemical properties of potential cathode material for Na-ion Batteries

The structural and electrochemical investigation of alluaudite-NaxFe3(PO4)(3) obtained by middle temperature solid-state synthesis is presented. XRD analysis with Rietveld refinement revealed contaminations for samples with x = 2.0. Reduction of the initial sodium content to x = 1.5 allowed to obtain single-phase Na1.47Fe3(PO4)(3) with real x value determined by iodometric titration. SEM images and particle size distribution showed the finegrained structure, which might have positive impact on kinetics of the charge/discharge processes. For the electrochemical properties investigation, the Na/Na+ /Na1.47Fe3(PO4)(3) cells were assembled. The cyclic charge/ discharge tests were carried out under various current loads showing high discharge capacity values (near the theoretical value 108 mAh/g) under C/10. For further analysis the CV tests with sodium diffusion coefficient evaluation using Randles-Sevcik equation was provided. The D value ( similar to 10(-14) cm(2) /s) allowed to state that the intercalation/deintercalation processes in alluaudite-NaxFe3(PO4)(3) are diffusion-limited.