Fig. 3: Structural evolution and charge compensation mechanism of NaVPO4F during cycling. | Nature Communications

Fig. 3: Structural evolution and charge compensation mechanism of NaVPO4F during cycling.

From: Development of vanadium-based polyanion positive electrode active materials for high-voltage sodium-based batteries

Fig. 3

a Operando SXRD diffraction patterns in the 6.0–16.5° 2Θ range (λ = 0.7239 Å). The SXPD pattern highlighted in bold shows the charged phase. The asterisk sign (*) designates the reflections belonging to coin-cell components. b Magnified regions of the operando SXRD intensity map. Horizontal full white and dashed black lines show the charged phase. c Cell volume evolution on charge/discharge as refined from the operando SXRD data. Error bars are within the circles. Major ticks mark every 20th pattern. d Corresponding charge-discharge profile in the Na||NaVPO4F cell, 1 M NaPF6 in EC:PC:FEC (47.5:47.5:5 by vol.) electrolyte, the second cycle, measurements were conducted at 22 ± 2 °C. e [001] ED patterns for the pristine material and recovered electrodes at 3.6, 4.5, and 2.0 V showing (dis)appearance of hk0: h + k = 2n + 1 reflections corresponding to the Pna21↔Pnan phase transition. f Ex situ EELS spectra for the harvested electrodes at OCV, charged to 4.5 V, and discharged to 2.0 V manifesting the reversible change of vanadium oxidation state. The V2O3 and VO2 spectra are given for reference.

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