Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2013 Jul 3;135(26):9898-906. doi: 10.1021/ja404189t. Epub 2013 Jun 24.
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.
AgNa(VO2F2)2 或 SSVOF 的结构和电化学分析。SSVOF 是完全有序的，并显示出电化学特性，为超越锂离子化学的储能电极设计提供了深入的了解。该化合物含有三氧化钒氟八面体，它们结合形成一维链状基本结构单元，这是钨铁矿（NaWO4）的特征。一维链堆积形成二维层；阳离子 Ag(+)和 Na(+) 位于这些层之间。通过使用极化率不同的阳离子（Ag(+)、Na(+)）来对氧化氟八面体进行有序排列。在钠离子电池的情况下，热力学上，与使用锂阳极相比，使用钠离子阳极会导致整个电池电压损失 300 mV；然而，通过将氟化物引入框架中，可以通过诱导效应提高还原电势来平衡这一点。这使得钠离子电池的电压可以与锂离子系统相媲美。以 SSVOF 为基准化合物，我们已经确定了新兴钠离子系统的新材料设计规则，这些规则不适用于锂离子系统。这些策略可以广泛应用于提供对基础结构化学感兴趣的材料和可观的钠离子电化学电压。
