Promoting Fast Ion Conduction in Li-Argyrodite through Lithium Sublattice Engineering

Fundamental understanding of ionic transport plays a pivotal role in designing and optimizing fast ionic conductors. Here, through a systematic neutron scattering and theoretical investigation, we discovered new insights about how anion sublattice affects Li + distribution and transport in Li-argyrodite. We found that the promotion of Li + conductivities is strongly correlated with a previously overlooked Li + interstitial site (16e), which is critical for realizing intercage Li + migration. More isotropic Li + migration pathways with higher Li + occupancies on the interstitial 16e site are found to be the underlying reason for the much higher Li + conductivity in Li 6 PS 5 Cl relative to the Br- and I-based analogues. We further confirm that they are also the universal driving force for the ultrahigh Li + conductivities in both anion-substituted Li-poor (Li 6– a PS 5– a X a, X = Cl and Br) and cation-substituted Li-rich argyrodite (e.g., Li 6+ a Ge a P 1– a S 5 I and Li 6+ a Si a Sb 1– a S 5 I). It is expected this strategy can be generally adopted to improve the ionic conductivity of the broad family of Li-rich argyrodite and beyond.