Redox paradox of vanadium in Tavorite LiVPO4F1-yOy : supplementary materials

<p>Vanadyl-type defects in vanadium oxy-fluoride phosphates confer interesting properties to these materials as positive electrodes in Li-ion or Na-ion batteries... <strong>List figures :</strong></p> <p><strong>2019-122-SM-FIGS1 :</strong> <strong>(a)</strong> Comparison of the SXRPD patterns obtained for the pristine LiVPO₄F_0.45O_0.55 material <em>in situ</em>, in the electrochemical cell, (blue) and in a sealed capillary (black). The symbols mark peaks not belonging to the LiVPO₄F_0.45O_0.55 phase (originating from lithium metal, beryllium, aluminum, PTFE, separator and Li₃V₂(PO₄)₃ impurity). The grey areas represent the excluded 2&theta; regions for Rietveld refinement. <strong>(b)</strong> Comparison between voltage profiles obtained <em>in situ </em>in electrochemical cells during the XRD and XAS experiments and in coin cells. The small features seen at 3.7 and 4.1V originate from the Li₃V₂(PO₄)₃ impurity.</p> <p><strong>2019-122-SM-FIGS2 :</strong> Rietveld refinement of (a) LiVPO₄F_0.45O_0.55 and (b) Li_0.45VPO₄F_0.45O_0.55, the PTFE contribution is represented by *. For (b) two phases are required to fit the pattern: LiVPO₄F_0.45O_0.55 (91(1) w%, blue markers) and Li_0.25VPO₄F_0.45O_0.55 (9(1) w% brown markers).</p> <p><strong>2019-122-SM-FIGS3 :</strong> Rietveld refinement of the last pattern obtained <em>operando</em> after Lithium deintercalation from LiVPO₄F_0.45O_0.55 (#126, corresponding to an overall composition of Li_0.2VPO₄F_0.45O_0.55): the refinement was performed considering a mixture of 3 phases, Li_0.45VPO₄F_0.45O_0.55 (orange), Li_0.25VPO₄F_0.45O_0.55 (brown) and VPO₄F_0.45O_0.55 (red), with their contributions being of 17(1), 58(1) and 25(1) wt.%, respectively. The peak highlighted by # corresponds to the LiV₂(PO₄)₃ impurity (<em>i.e.</em> delithiated form of Li₃V₂(PO₄)₃). For the refinement, the profile and the atomic position of the secondary phases (i.e. LiVPO₄F_0.45O_0.55and VPO₄F_0.45O_0.55) have been fixed based on their individual refinements (i.e. pattern #86 and <em>ex situ fully charged </em>pattern) whereas the cell parameters, profile and atomic positions of Li_0.25VPO₄F_0.45O_0.55have been refined independently.</p> <p><strong>2019-122-SM-FIGS4 : (a)</strong> SXRPD patterns obtained <em>operando</em> during lithium extraction from LiVPO₄F_0.25O_0.75, <strong>(b)</strong> Selected SXRPD patterns at specific compositions.</p> <p><strong>2019-122-SM-FIGS5 : </strong>Evolution of the volume changes for each Li_xVPO₄F_1-yO_y sample as function of x during the first step of the charge (i.e. until &Delta;x = y).</p> <p><strong>2019-122-SM-FIGS6 : (a)</strong> The evolution of the pre-edge intensity (obtained by integration of the signal from 5464 to 5474 eV) and the edge position (taken at half jump) upon cycling.<strong> (b)</strong> The variance plot justifying the use of three components.</p> <p><strong>2019-122-SM-FIGS7 : (a)</strong> V K-edge XANES spectra of several Tavorite-type references: LiV^IIIPO₄F (black line), LiV^IVPO₄O (grey line), V^IVPO₄F (orange line) and V^VPO₄O (red line) and LiVPO₄F_0.45O_0.55 (purple line). <strong>(b)</strong> The enlargement of the pre-edge region with the typical energy position of each pre-edge contributions (<em>i.e.</em> F-V³⁺O₄-F, O=V⁴⁺O₄&mdash;O and O=V⁵⁺O₄&mdash;O)</p> <p><strong>2019-122-SM-FIGS8 : </strong>Magnitude of the Fourier transforms of the reconstructed components obtained by MCR-ALS (k-range: 2.7-12.7 &Aring;^-1, sine window). Li_xVPO₄F_0.45O_0.55 with x = 1, 0.45 and 0 respectively for components #1, #2 and #3. The black lines represent the fit done in the R space (R range: 1.0 &ndash; 2.05 &Aring;, dR = 0.1 &Aring;, sine window).</p> <p>&nbsp;</p> <p>&nbsp;</p> <p>&nbsp;</p> <p>&nbsp;</p> <p>&nbsp;</p> <p>&nbsp;</p>