Abstract
by a one-step hydrothermal synthesis route. The physical properties and structure
of this material were obtained through XRD and Mössbauer analyses. X-ray diffraction Rietveld
refinements confirm a cationic distribution of Na+ and presence of vacancies in A(2)’, Na+ and
small amounts of Mn2+ in A(1), Mn2+ in M(1) , 0.5 Mn2+ and Fe cations (Mn2+,Fe2+ and Fe3+) in
M(2), leading to the structural formula Na2Mn(Mn0.5Fe1.5)(PO4)3. The particles morphology was
investigated by SEM. Several reactions with different hydrothermal reaction times were
attempted to design a suitable synthesis protocol of NMFP compound. The time of reaction was
varied from 6 to 48 hours at 220°C. The pure phase of NMFP particles was firstly obtained when
the hydrothermal reaction of NMFP precursors mixture was maintained at 220°C for 6 hours.
When the reaction time was increased from 6 to 12, 24 and 48 hours, the dandelion structure was
destroyed in favor of NMFP micro-rods. The combination of NMFP (NMFP-6H, NMFP-12H,
NMFP-24H and NMFP-48H) structure refinement and Mössbauer characterizations shows that
the increase of the reaction time leads to the progressive increment of Fe(III) and the decrease of
the crystal size. The electrochemical tests indicated that NMFP is a 3 V sodium intercalating
cathode. The comparison of the discharge capacity evolution of studied NMFP electrode
materials at C/5 current density shows different capacities of 48, 40, 34 and 34 mAhg-1 for
NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H respectively. Interestingly, all samples
show excellent capacity retention of about 99 % during 50 cycles.
