Na3V2(PO4)2F3 has the potential to deintercalate 3 sodium ions, but only two have been experimentally observed to be electrochemically active. The extraction of the third one would require a potential too high, where common electrolytes are not stable. Moreover, Na3V2(PO4)2F3 actually belongs to a full solid solution Na3V2(PO4)2F3-2xO2x [3], where the whole family delivers good performances as positive electrodes for Na-ion batteries, thanks to the active redox couple shifting from V3+/V4 to V4+/V5+. This means a very high degree of flexibility is present in this class of materials. To improve their performances even further, we considered a doping strategy with different transition metals to replace part of the vanadium into the structure, in the attempt at lowering such potential; in this presentation we will show the results of our doping from the predictions of ab initio calculations to the actual synthesis. The best strategies will be presented and the improvement they bring in terms of energy density and/or Na ion kinetics highlighted.
References
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[8] M. Bianchini, N. Brisset, F. Fauth, F. Weill, E. Suard, C. Masquelier and L. Croguennec, Chemistry of Materials (2015), 27(8), 3009-3020.