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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.

The potassium vanadium oxide-fluoride phase β-KVOF3 was prepared by in-situ reduction with hydrothermal methods and characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. The compound is orthorhombic [space group Pnma, a = 7.1596(2) Å, b = 7.5392(2) Å, c = 13.0506(4) Å, Z = 8]. The material is structurally similar and isoformulaic to d1 materials of formulae AVOF3 ( A+ = alkali metal, ammonium, or organic cation). Magnetic susceptibility data were successfully fit with a Heisenberg chain model. In-situ reduction of V5+ to V4+ during the hydrothermal reaction conditions was observed in the presence of Br- anions. The role of bromide ions in this reduction is explained and employed to reduce a d0 vanadium species to obtain a material with magnetic behavior. [ABSTRACT FROM AUTHOR]

The potassium vanadium oxide-fluoride phase β-KVOF3 was prepared by in-situ reduction with hydrothermal methods and characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. The compound is orthorhombic [space group Pnma, a = 7.1596(2) Å, b = 7.5392(2) Å, c = 13.0506(4) Å, Z = 8]. The material is structurally similar and isoformulaic to d1 materials of formulae AVOF3 ( A+ = alkali metal, ammonium, or organic cation). Magnetic susceptibility data were successfully fit with a Heisenberg chain model. In-situ reduction of V5+ to V4+ during the hydrothermal reaction conditions was observed in the presence of Br- anions. The role of bromide ions in this reduction is explained and employed to reduce a d0 vanadium species to obtain a material with magnetic behavior. [ABSTRACT FROM AUTHOR]

Non-centrosymmetric NaVOF4(H2O) (I) and NaVO2-xF2+x (II; x = 1/3) are prepared from an 1:1:4 molar mixture of V2O5, NaCl, and HF (teflon container, 100 °C, 30 min for (I) and 150 °C, 24 h for (II)). [ABSTRACT FROM AUTHOR]

β-KVOF3 is prepared by in-situ reduction under hydrothermal conditions using a mixture of V2O5 and KBr (3:2) in aq. [ABSTRACT FROM AUTHOR]

Crystals and powder of AgNa(VO2F2)2 (I) are prepared by hydrothermal synthesis of a stoichiometric mixture of Ag2O, NaF, and V2O5 in aqueous HF (autoclave, 150 °C, 24 h, 40% yield). [ABSTRACT FROM AUTHOR]

The new compounds (IV) and (VI) crystallize isostructurally in the monoclinic space group P21/c with Z = 2 (single crystal XRD). [ABSTRACT FROM AUTHOR]