Iron substitution in Na4VMn(PO4)3 as a strategy for improving the electrochemical performance of sodium-ion batteries

Abstract Six NASICON type samples with Na4-xVFexMn1-x(PO4)3 (0 ≤ x ≤ 1) stoichiometry are examined as positive electrodes for sodium-ion batteries. The structural, morphological, and chemical state of elements in raw samples is unveiled by XRD diffraction, electron microscopy, and Raman and XPS spectroscopies. The effect of the dual Fe/Mn substitution is examined by electrochemical tests using both voltammetric and galvanostatic methods. The results reveal the beneficial effect of the iron substitution, justified by an improvement of the kinetic response, and supported by the calculation of the apparent diffusion coefficients and internal cell resistance.