Li6SiO4Cl2: A Hexagonal Argyrodite Based on Antiperovskite Layer Stacking

A hexagonal analogue, Li6SiO4Cl2, of the cubic lithium argyrodite family of solid electrolytes is isolated by a computation-experiment approach. We show that the argyrodite structure is equivalent to the cubic antiperovskite solid electrolyte structure through anion site and vacancy ordering within a cubic stacking of two close-packed layers. Construction of models that assemble these layers with the combination of hexagonal and cubic stacking motifs, both well known in the large family of perovskite structural variants, followed by energy minimization identifies Li6SiO4Cl2 as a stable candidate composition. Synthesis and structure determination demonstrate that the material adopts the predicted lithium site-ordered structure with a low lithium conductivity of similar to 10(-10) S cm(-1) at room temperature and the predicted hexagonal argyrodite structure above an order-disorder transition at 469.3(1) K. This transition establishes dynamic Li site disorder analogous to that of cubic argyrodite solid electrolytes in hexagonal argyrodite Li6SiO4Cl2 and increases Li-ion mobility observed via NMR and AC impedance spectroscopy. The compositional flexibility of both argyrodite and perovskite alongside this newly established structural connection, which enables the use of hexagonal and cubic stacking motifs, identifies a wealth of unexplored chemistry significant to the field of solid electrolytes.

Automated summary

A hexagonal analogue of the cubic lithium argyrodite family of solid electrolytes, Li6SiO4Cl2, is isolated using a computation-experiment approach. The material exhibits low lithium conductivity at room temperature and undergoes a structure transition at a predicted temperature. This newly established structural connection between hexagonal and cubic stacking motifs opens up unexplored chemistry significant to the field of solid electrolytes.