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 synchrotron/neutron 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.

Argyrodites, Li6PS5X (X = Cl, Br), are considered to be one of the most promising solid-state electrolytes for solid-state batteries. However, while traditional ball-mill approaches to prepare these materials do not promote scale-up, solution-based preparative methods have resulted in poor ionic conductivity. Herein, we report a solution-engineered, scalable approach to these materials, including the new argyrodite solid solution phase Li6–y PS5–y Cl1+y (y = 0–0.5), that shows very high ionic conductivities (up to 3.9 mS·cm–1) and negligible electronic conductivities. These properties are almost the same as their analogues prepared by solid-state methods, owing to a lack of amorphous contributions and low impurity contents ranging from 3 to 10%. Electrochemical performance is demonstrated for Li6PS5Cl in a prototype solid-state battery and compared to that of the same solid electrolyte derived from classic ball-milling processing.

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A new disordered chlorospinel superionic conductor, Li2Sc2/3Cl4, enables high-voltage all solid state batteries up to 4.6 V vs. Li+/Li.