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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.

A detailed structural characterization is performed on β-Li3PS4 using 6Li and 31P magic-angle spinning NMR spectroscopy in combination with X-ray and neutron diffraction. High-temperature synchrotron X-ray diffraction was used to determine the phase stability and observe phase transitions. In addition, we investigated the Li+-ion dynamics by temperature-dependent 7Li NMR lineshape analysis, 7Li NMR relaxometry, and 7Li pulsed field-gradient (PFG) NMR measurements. A good agreement is obtained between the local hopping observed by T 1 relaxation time measurements and the long-range transport investigated by PFG NMR with a Li+ diffusion coefficient of 9 × 10–14 m2/s at 298 K and an activation energy of 0.24 eV. From this, a Li+ conductivity of 1.0 × 10–4 S/cm is estimated, which corresponds well with impedance measurements on β-Li3PS4 pellets.

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