Correlating Structural Disorder to Li<sup>+</sup> Ion Transport in Li<sub>4–<i>x</i></sub>Ge<sub>1–<i>x</i></sub>Sb<sub><i>x</i></sub>S<sub>4</sub> (0 ≤ <i>x</i> ≤ 0.2)
Bianca Helm, Nicolò Minafra, Björn Wankmiller, Matthias T. Agne, Cheng Li, Anatoliy Senyshyn, Michael Ryan Hansen, Wolfgang G. Zeier
Abstract
Strong compositional influences are known to affect the ionic transport within the thio-LISICON family; however, a deeper understanding of the resulting structure–transport correlations has up until now been lacking. Employing a combination of high-resolution neutron diffraction, impedance spectroscopy, and nuclear magnetic resonance spectroscopy, together with bond valence site energy calculations and the maximum entropy method for determining the underlying Li+ scattering density distribution of a crystal structure, this work assesses the impact of the Li+ substructure and charge carrier density on the ionic transport within the Li4–xGe1–xSbxS4 substitution series. By incorporating Sb5+ into Li4GeS4, an anisometric expansion of the unit cell is observed. An additional Li+ position is found as soon as (SbS4)3– polyhedra are present, leading to a better local polyhedral connectivity and a higher disorder in the Li+ substructure. Here, we are able to relate structural disorder to an increase in configurational entropy, together with a 2 order-of-magnitude increase in ionic conductivity. This result reinforces the typically believed paradigm that structural disorder leads to improvements in ionic transport.