Density Functional Theory-Assisted ³¹P and ²³Na Magic-Angle Spinning Nuclear Magnetic Resonance Study of the Na₃V₂(PO₄)₂F₃–Na₃V₂(PO₄)₂FO₂ Solid Solution: Unraveling Its Local and Electronic Structures

Abstract

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Local atomic and electronic structure in the LiVPO4(F,O) tavorite‐type materials from solid‐state NMR combined with DFT calculations

“…The ST is strong due to the local electronic structure and to the contribution of both vanadium octahedra sharing an edge with the lithium polyhedra. [ 7 ] In the case of LiV IV PO 4 O, the presence of vanadyl bonds along the z‐direction, indicated in the inset of Figure 2, induces a lift of degeneracy of the t 2g orbitals: the d z2 and one of the d xz /d yz orbitals are involved in the strong covalent V IV O vanadyl bond, while the d xy orbital is stabilized and is the one carrying the unpaired electron [ 7,12 ] (as described in Figure S2). Therefore, in LiVPO 4 O, an ST mechanism from V IV to Li can occur only from the d xy orbital through the O–O edge shared with V a (see Figure 2a).…”

“…[7] Further details concerning the Fermi contact shifts calculations using this method can be found in previous works. [7,12,13] To model the substituted phases, several O/F arrangements based on a 128-atom supercell (2a × 2b × 2c) were used for LiVPO 4 F 0.25 O 0.75 , LiVPO 4 F 0.5 O 0.5 , or LiVPO 4 F 0.75 O 0.25 compositions. The structure of the supercell was relaxed using GGA + U, and the different local electronic structures were analyzed.…”

Challenges of today for Na-based batteries of the future: From materials to cell metrics

“…In both cases, the average operating voltage is driven to lower values, thus, resulting in lower energy densities. Nuclear Magnetic Resonance (NMR) and Infra-Red (IR) spectroscopies were shown to be the tools of choice to track the presence of oxygen defects and vanadyl bonds ({V 4+ =O} 2+ ) in Na 3 V 2 (PO 4 ) 2 F 3 , allowing to control the synthesis of the optimized active material [57,58]. In fact, most of the reported work on Na 3 V 2 (PO 4 ) 2 F 3 often deals with compositions that are highly oxygen-rich, i.e.…”

Fluorophosphates: Next Generation Cathode Materials for Rechargeable Batteries

“…[159] The solid solution was further studied by density functional theory method and 31 P and 23 Na magic-angle spinning NMR study. [160] They observed complex spin transfer mechanism between the two materials because of the peculiar nature of electronic structure of V-ions.…”