Atomic Structure and Kinetics of NASICON Na_xV₂(PO₄)₃ Cathode for Sodium‐Ion Batteries

Abstract

Key indicators: single-crystal X-ray study; T = 293 K; mean (P-O) = 0.001 A ˚ ; disorder in solvent or counterion; R factor = 0.032; wR factor = 0.075; data-to-parameter ratio = 36.0. Single crystals of the title compound, trisodium divanadium-(III) tris(orthophosphate), were grown from a self-flux in the system Na 4 P 2 O 7-NaVP 2 O 7. Na 3 V 2 (PO 4) 3 belongs to the family of NASICON-related structures and is built up from isolated [VO 6 ] octahedra (3. symmetry) and [PO 4 ] tetrahedra (.2 symmetry) interlinked via corners to establish the framework anion [V 2 (PO 4) 3 ] 3À. The two independent Na + cations are partially occupied [site-occupancy factors = 0.805 (18) and 0.731 (7)] and are located in channels with two different oxygen environments, viz sixfold coordination for the first (3. symmetry) and eightfold for the second (.2 symmetry) Na + cation. Related literature For structures and properties of complex phosphates with general formula Na 3 M III 2 (PO 4) 3 (M III = Sc, Fe, Cr), see: Collin et al. (1986); Genkina et al. (1991); Lazoryak et al. (1980); Lucazeau et al. (1986); Masquelier et al. (1992); Susman et al. (1983). For preparation of NaVP 2 O 7 which was used as an educt for crystal growth of the title compound, see: Zatovsky et al. (1999). Experimental Crystal data Na 3 V 2 (PO 4) 3 M r = 455.76 Trigonal, R3c a = 8.7288 (2) A ˚ c = 21.8042 (7) A ˚ V = 1438.73 (7) A ˚ 3 Z = 6 Mo K radiation = 2.66 mm À1 T = 293 K 0.20 Â 0.15 Â 0.10 mm Data collection Oxford Diffraction Xcalibur-3 CCD diffractometer Absorption correction: multi-scan (Blessing, 1995) T min = 0.635, T max = 0.780 12580 measured reflections 1331 independent reflections 1153 reflections with I > 2(I) R int = 0.063

Electrospun NaVPO4F/C Nanofibers as Self‐Standing Cathode Material for Ultralong Cycle Life Na‐Ion Batteries

“…The peak of 3.42 V can be ascribed to sodium insertion into Na 1−x VPO 4 F (Na 1−x VPO 4 F + xNa + + xe − → NaVPO 4 F, 0 < x ≤ 1), the chemical state of vanadium decreased. What is more, it is rather remarkable that the redox peaks of the first three cycles are highly overlapping and the peak separation value (ΔE) is much smaller (0.24 V) than previous reports, [20][21][22] indicating the fast redox kinetics and good reversibility of Na + extraction/insertion. This is resulted from that NaVPO 4 F/C with 3D conductive network and small nanoparticles can reduce the resistance of transporting Na + ion and electrons efficiently.…”

Reduced Graphene Oxide Decorated Na3V2(PO4)3 Microspheres as Cathode Material With Advanced Sodium Storage Performance

“…Furthermore, sodium resource is abundant on earth and the price is cheap. Thus, SIBs are considered as the most promising competitive alternative to LIBs (Jian et al, 2014; Wang H. et al, 2015; Chao et al, 2016; Xu et al, 2016). Developing SIBs with excellent electrochemical performance becomes necessary and challenging.…”

Sodium vanadium titanium phosphate electrode for symmetric sodium-ion batteries with high power and long lifespan

“…1a, NASICON-structured phosphates Na 2 MM′(PO 4 ) 3 are constructed by the ‘lantern-like’ units sequenced along the c axis, which are composed by two [MO 6 ]/[M′O 6 ] octahedra and three [PO 4 ] tetrahedra by sharing all their corners6. This robust framework provides a three-dimensional diffusion pathway for Na + ions with controllable lattice expansion below 8% (refs 7, 8), which is believed beneficial for the cycling stability. Furthermore, the strong inductive effect of polyanion allows to monitor the M n + /M ( n −1)+ redox pair and gives rise to higher working potential versus Na + /Na than in oxides.…”