Effect of the Particles Morphology on the Electrochemical Performance of Na₃V₂(PO₄)₂F_3‐yO_y

Abstract

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.

Particle nanosizing and coating with an ionic liquid: two routes to improve the transport properties of Na3V2(PO4)2FO2

“…14,36,41,56 Meanwhile, the broader signal for NVPFO 2 -Nano could be the consequence of disorder due to particle downsizing. 34 31 P ss-NMR spectra obtained for all NVPFO 2 show a very intense signal at ∼0 ppm corresponding to the P(OV 4+ ) 4 local environment (Fig. 5b).…”

“…[22][23][24][25][26][27][28] and morphology design (flower, sand rose, nano/micro-sphere, nano/micro-cube, etc.) [29][30][31][32][33][34] have been proposed to overcome this problem. Among the various synthesis methods, morphology control and hybridization with a carbon-based conductive phase are often carried out by hydrothermal/solvothermal synthesis.…”

“…Among the various synthesis methods, morphology control and hybridization with a carbon-based conductive phase are often carried out by hydrothermal/solvothermal synthesis. 34,35 However, this synthesis process leads most often to partial oxidation of vanadium and to a V 3+ /V 4+ ratio difficult to be controlled in the final composition, which drastically affects the energy storage performance and thus makes it difficult to evaluate the sole influence of morphology. 34,[36][37][38][39] Recently, Olchowka et al have reported an original ionothermal synthesis method leading to NVPFO 2 particles coated with an EMI TFSI ionic liquid (IL).…”

“…34,35 However, this synthesis process leads most often to partial oxidation of vanadium and to a V 3+ /V 4+ ratio difficult to be controlled in the final composition, which drastically affects the energy storage performance and thus makes it difficult to evaluate the sole influence of morphology. 34,[36][37][38][39] Recently, Olchowka et al have reported an original ionothermal synthesis method leading to NVPFO 2 particles coated with an EMI TFSI ionic liquid (IL). 40 Their energy storage performance appears promising, even if the effect of IL coating is not fully understood yet.…”

Hierarchical Na3V2(PO4)2F3 Microsphere Cathodes for High-Temperature Li-Ion Battery Application

“… 18 − 21 Recently, Fang et al, in 2022, reported morphological impact on Na 3 V 2 (PO 4 ) 2 F 3 cathode performances for Na-ion batteries. 22 The micro-/nanostructure morphology of the Na 3 V 2 (PO 4 ) 2 F 3 cathode designed by one-pot hydro-/solvothermal method without any high-temperature treatment has received great attention as it reduces the time, energy, and controls the particle size. 23 , 24 Recently, the synthesis of hierarchical micro-/nanostructures of Na 3 V 2 (PO 4 ) 2 F 3 morphology has attracted attention for designing Li-/Na-ion batteries due to their extraordinary properties that suppress particle agglomeration; low volume expansion leads to better electrical conductivity and diffusivity.…”