Enhancement of Low Temperature Superionic Conductivity by Suppression of Li Site Ordering in Li 7 Si 2-x Ge x S 7 I

• Published in: Angewandte Chemie International Edition 2024-09, Vol.63 (37), p.e202409372
• Main Authors: Han, Guopeng, Daniels, Luke M, Vasylenko, Andrij, Morrison, Kate A, Corti, Lucia, Collins, Chris M, Niu, Hongjun, Chen, Ruiyong, Roberston, Craig M, Blanc, Frédéric, Dyer, Matthew S, Claridge, John B, Rosseinsky, Matthew J
• Format: Article
• Language: English
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202409372

Ge substitution into the recently discovered superionic conductor Li Si S I is demonstrated by synthesis of Li Si Ge S I, where x≤1.2. The anion packing and tetrahedral silicon location of Li Si S I are retained upon substitution. Single crystal X-ray diffraction shows that substitution of larger Ge for Si expands the unit cell volume and further increases Li site disorder, such that Li Si Ge S I has one Li site more (sixteen in total) than Li Si S I. The ionic conductivity of Li Si Ge S I (x=1.2) at 303 K is 1.02(3)×10  S cm with low activation energies for Li transport demonstrated over a wide temperature range by AC impedance and Li NMR spectroscopy. All sixteen Li sites remain occupied to temperatures as low as 30 K in Li Si Ge S I as a result of the structural expansion. This differs from Li Si S I, where the partial Li site ordering observed below room temperature reduces the ionic conductivity. The suppression of Li site depopulation by Ge substitution retains the high mobility to temperatures as low as 200 K, yielding low temperature performance comparable with state-of-the-art Li ion conducting materials.