Atomistic Characterisation of Li+ Mobility and Conductivity in Li7-xPS6-xIx Argyrodites from Molecular Dynamics Simulations, Solid-State NMR, and Impedance Spectroscopy
Atomistic Characterisation of Li+ Mobility and Conductivity in Li7-xPS6-xIx Argyrodites from Molecular Dynamics Simulations, Solid-State NMR, and Impedance Spectroscopy
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DOI：
10.1002/chem.201000501
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Zahn, Dirk
中科院分区：
文献类型：
--
作者：
Pecher, Oliver;Kong, Shiao-Tong;Zahn, Dirk
从实验和理论两个方面探讨了Li ~（7-x）PS ~（6-x）Ix银氧化物中Li ~+离子迁移率/电导率的原子机制。标题化合物中的离子导电性与固-固相变有关，其特征在于低温差示扫描量热法，Li-7和I-127 NMR研究，阻抗测量和分子动力学模拟。两种同位素的核磁共振信号在低温下都是由各向异性相互作用主导的。NMR信号的显著变窄表明在177 +/- 2 K以上各向异性相互作用的运动平均。从阻抗谱和分子动力学模拟的活化能离子电导率进行了评估。后者揭示了一系列的间隙网站变得可访问的Li+离子，而其余的离子留在各自的网站在argyrodite晶格。间隙位置各自对应于S/I原子四面体的中心，并且仅在它们与相邻PS4四面体的共同角、边或面方面有所不同。从连接性分析和自由能排名，一个特定的四面体被确定为离子电导率的关键限制，并明确区分从本地流动性，这遵循一个不同的机制与低得多的活化能。从X射线衍射实验得到的晶格参数的插值表明Li 7-xPS 6-xIx的均匀性范围为0.97
The atomistic mechanisms of Li+ ion mobility/conductivity in Li7-xPS6-xIx argyrodites are explored from both experimental and theoretical viewpoints. Ionic conductivity in the title compound is associated with a solid solid phase transition, which was characterised by low-temperature differential scanning calorimetry, Li-7 and I-127 NMR investigations, impedance measurements and molecular dynamics simulations. The NMR signals of both isotopes are dominated by anisotropic interactions at low temperatures. A significant narrowing of the NMR signal indicates a motional averaging of the anisotropic interactions above 177 +/- 2 K. The activation energy to ionic conductivity was assessed from both impedance spectroscopy and molecular dynamics simulations. The latter revealed that a series of interstitial sites become accessible to the Li+ ions, whilst the remaining ions stay at their respective sites in the argyrodite lattice. The interstitial positions each correspond to the centres of tetrahedra of S/I atoms, and differ only in terms of their common corners, edges, or faces with adjacent PS4 tetrahedra. From connectivity analyses and free-energy rankings, a specific tetrahedron is identified as the key restriction to ionic conductivity, and is clearly differentiated from local mobility, which follows a different mechanism with much lower activation energy. Interpolation of the lattice parameters as derived from X-ray diffraction experiments indicates a homogeneity range for Li7-xPS6-xIx with 0.97