AgNa(VO₂F₂)₂: A Trioxovanadium Fluoride with Unconventional Electrochemical Properties

Abstract

We present structural and electrochemical analyses of a new double-wolframite compound: AgNa(VO2F2)2 or SSVOF. SSVOF is fully ordered and displays electrochemical characteristics that give insight into electrode design for energy storage beyond lithium-ion chemistries. The compound contains trioxovanadium fluoride octahedra that combine to form one-dimensional chain-like basic building units, characteristic of wolframite (NaWO4). The 1D chains are stacked to create 2D layers; the cations Ag(+) and Na(+) lie between these layers. The vanadium oxide-fluoride octahedra are ordered by the use of cations (Ag(+), Na(+)) that differ in polarizability. In the case of sodium-ion batteries, thermodynamically, the use of a sodium anode introduces a 300 mV loss in overall cell voltage as compared to a lithium anode; however, this can be counter-balanced by introduction of fluoride into the framework to raise the reduction potentials via an inductive effect. This allows sodium-ion batteries to have comparable voltages to lithium systems. With SSVOF as a baseline compound, we have identified new materials design rules for emerging sodium-ion systems that do not apply to lithium-ion systems. These strategies can be applied broadly to provide materials of interest for fundamental structural chemistry and appreciable voltages for sodium-ion electrochemistry.

Reactivity of VOF3 with N-Heterocyclic Carbene and Imidazolium Fluoride: Analysis of Ligand–VOF3 Bonding with Evidence of a Minute π Back-Donation of Fluoride

“…Compounds with a [VO 2 F 2 ] − anion are usually obtained from the reaction between vanadium oxides or other vanadates with hydrofluoric acid, − but such an approach usually yields an anion in oligomeric or polymeric form in practically all known crystal structures, except [Ph 4 M]­[VO 2 F 2 ] (M = P, As), [{VO­(salen)} 2 ­(μ-F)]­[VO 2 F 2 ], and [Et 4 N] 6 ­[HV 22 O 54 ­(VO 2 F 2 )] . We were able to prepare crystals of [(L Dipp )­H]­[VO 2 F 2 ] ( 3 ) salt through the reaction of L Dipp and VOF 3 in THF.…”

Syntheses of Two Vanadium Oxide–Fluoride Materials That Differ in Phase Matchability

“…This is consistent with hard/soft acid/base interactions that have been previously observed and discussed. 9 , 23 , 24 , 45 − 49 …”

Antiferromagnetic Semiconductor BaFMn0.5Te with Unique Mn Ordering and Red Photoluminescence

“…LaCa 2 GeS 4 Cl 3 , Ba 3 AGa 5 Se 10 Cl 2 (A = Cs, Rb, K), and Ba 3 P 3 O 10 X (X = Cl, Br) exhibit strong nonlinear optical responses. FeOF, , AgNa­(VO 2 F 2 ) 2 , argyrodites Li 6 PS 5 X (X = Cl, Br, I), , and anti-perovskite Li 3 OCl are promising for battery applications. BiOCuSe, which adopts the 2D ZrCuSiAs-type structure, is a promising candidate in thermoelectric applications. , …”