New Family of Argyrodite Thioantimonate Lithium Superionic Conductors

摘要

We report on a new family of argyrodite lithium superionic conductors, as solid solutions Li_(6+x )M_(x )Sb_(1–x )S_(5)I (M = Si, Ge, Sn), that exhibit superionic conductivity. These represent the first antimony argyrodites to date. Exploration of the series using a combination of single crystal X-ray and synchrotroneutron powder diffraction, combined with impedance spectroscopy, reveals that an optimal degree of substitution (x ), and substituent induces slight S~(2–)/I~(–) anion site disorder—but more importantly drives Li~(+) cation site disorder. The additional, delocalized Li-ion density is located in new high energy lattice sites that provide intermediate interstitial positions (local minima) for Li~(+) diffusion and activate concerted ion migration, leading to a low activation energy of 0.25 eV. Excellent room temperature ionic conductivity of 14.8 mS·cm~(–1) is exhibited for cold-pressed pellets—up to 24 mS·cm~(–1) for sintered pellets—among the highest values reported to date. This enables all-solid-state battery prototypes that exhibit promising properties. Furthermore, even at −78 °C, suitable bulk ionic conductivity of the electrolyte is retained (0.25 mS·cm~(–1)). Selected thioantimonate iodides demonstrate good compatibility with Li metal, sustaining over 1000 h of Li stripping/plating at current densities up to 0.6 mA·cm~(–2). The significantly enhanced Li ion conduction and lowered activation energy barrier with increasing site disorder reveals an important strategy toward the development of superionic conductors.