采用紫外?可见吸收光谱表征Na3(VO1?xPO4)2F1＋2x(0≤x≤1)中钒的表观价态，用X射线衍射精修所得晶胞参数对紫外?可见光谱法的表征结果进行验证. 结果表明，Na3(VOPO4)2F中钒的表观价态为+3.993, Na3(VO0.5PO4)2F2和Na3(VOPO4)2F3中钒的价态分别为+3.097和+3.603，紫外?可见吸收光谱法得到的结果是可信的.
Sodium vanadium fluorophosphates, Na3(VO1?xPO4)2F1+2x (0≤x≤1), have obtained widespread attention as cathode materials for sodium ion batteries, because of its electrochemical stability, high working voltage and specific capacity. In Na3(VO1?xPO4)2F1+2x (0≤x≤1), the valence state of vanadium is flexible, it could be +3, +4 or mixed valence of +3 and +4. When x=1, the valence state of vanadium is +3, the formula could be written as Na3(VPO4)2F3. When x=0, the valence state of vanadium is +4, the formula could be written as Na3(VOPO4)2F. When 0<x<1, the valence state of vanadium would be mixed valence between +3 and +4, the compound is solid solution of Na3(VPO4)2F3 and Na3(VOPO4)2F. Valence state of vanadium is directly related to the crystal structure and electrochemical properties of Na3(VO1?xPO4)2F1+2x (0≤x≤1), so characterize valence of vanadium in Na3(VO1?xPO4)2F1+2x (0≤x≤1) precisely is of great significant. Various methods have been used to characterize the valence state of vanadium in Na3(VO1?xPO4)2F1+2x (0≤x≤1), such as X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, Rietveld X-ray diffraction, 31P nuclear magnetic resonance, 23Na nuclear magnetic resonance, 19F nuclear magnetic resonance and X-ray adsorption near edge structure. However, all those methods need expensive equipment and complicate data processing. To characterize valence state of vanadium in an easier way, a new method to use UV?Vis absorption to characterize the valence of vanadium in Na3(VO1?xPO4)2F1+2x (0≤x≤1) was developed in this work. Crystal parameters obtained from Rietveld XRD had been used to confirm the results obtained by UV?Vis absorption spectra. The results showed that the valence states of Na3(VOPO4)2F, Na3(VO0.5PO4)2F2 and Na3(VPO4)2F3 were +3.993, +3.097 and +3.603, it was credible for UV?Vis absorption spectra to be used to characterize apparent valence of vanadium.
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