Effect of the Particles Morphology on the Electrochemical Performance of Na 3 V 2 (PO 4 ) 2 F 3‐y O y

Among all the positive electrode materials explored for Na-ion batteries, the family of Na3VIII2-y(VIVO)y(PO4)2F3-y (NVPFOy) has attracted extensive attention for its high operating voltage and structural stability. In order to promote better performance at high rates, it appears interesting to consider the correlation between NVPFOy’s composition, morphology (size and shape) and electrochemical properties. Here, solvothermal syntheses were considered in order to obtain a series of NVPFOy compounds showing different morphologies (such as nanospheres, flakes, cylindrical aggregates or desert-roses) by playing on different synthesis parameters like water/ethanol ratio, stoichiometry of the precursors’ mixture, heating rate, and the presence or not of a surfactant. Four compounds presenting different morphology have been fully characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared, NMR and XPS spectroscopies. Their electrochemical properties are studied using electrodes rich in active material in order to better observe the influence of the morphology on the energy storage performance and are compared to those of Na3V2(PO4)2F3 and Na3V2(PO4)2FO2 reference materials obtained by solid-state synthesis and with shapeless morphology.