Influence of Lattice Polarizability on the Ionic Conductivity in the Lithium Superionic Argyrodites Li6PS5X (X = Cl, Br, I)
Influence of Lattice Polarizability on the Ionic Conductivity in the Lithium Superionic Argyrodites Li6PS5X (X = Cl, Br, I)
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DOI：
10.1021/jacs.7b06327
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发表时间：
2017-08-09
影响因子：
15
通讯作者：
Zeier, Wolfgang G.
中科院分区：
文献类型：
--
作者：
Kraft, Marvin A.;Culver, Sean P.;Zeier, Wolfgang G.
在寻找用于固态电池的新型固体电解液的过程中，硫代磷酸盐离子导体由于其高的离子电导率而成为最近的关注焦点，据信这是由于更柔软、更可极化的阴离子骨架所致。受到经常提到的软阴离子晶格和离子输运之间的联系的启发，这项工作旨在提供证据，说明改变一种结构中阴离子亚晶格的极化率如何影响离子输运。在这里，我们通过控制卤化物阴离子(X=Cl，Br，I)的占有率来系统地改变上离子银氧化物Li6PS5X的阴离子骨架极化率。声速测量被用来量化晶格刚度和德拜频率的变化。结合电化学阻抗谱和中子衍射谱，这些结果表明，晶格的柔软性对离子输运有显著的影响：较软键降低了活化势垒，同时降低了移动离子的前因子。由于这些参数对离子电导率的影响是相互矛盾的，我们发现为了获得最佳的离子电导率，有必要调整材料的晶格硬度。
In the search for novel solid electrolytes for solid-state batteries, thiophosphate ionic conductors have been in recent focus owing to their high ionic conductivities, which are believed to stem from a softer, more polarizable anion framework. Inspired by the oft-cited connection between a soft anion lattice and ionic transport, this work aims to provide evidence on how changing the polarizability of the anion sublattice in one structure affects ionic transport. Here, we systematically alter the anion framework polarizability of the superionic argyrodites Li6PS5X by controlling the fractional occupancy of the halide anions (X = Cl, Br, I). Ultrasonic speed of sound measurements are used to quantify the variation in the lattice stiffness and Debye frequencies. In combination with electrochemical impedance spectroscopy and neutron diffraction, these results show that the lattice softness has a striking influence on the ionic transport: the softer bonds lower the activation barrier and simultaneously decrease the prefactor of the moving ion. Due to the contradicting influence of these parameters on ionic conductivity, we find that it is necessary to tailor the lattice stiffness of materials in order to obtain an optimum ionic conductivity.