The Siso/Stot fraction appears to be a reliable descriptor of fast ion transport in glassy sulfide systems over a wide range of ionic conductivities and cation diffusivities. Using pulsed neutron diffraction and Raman spectroscopy supported by first principles simulations, we show that preferential diffusion pathways in vitreous sodium and silver sulfides are related to isolated sulfur Siso, that is, the sulfur species surrounded exclusively by mobile cations with a typical stoichiometry of M/Siso ≈ 2. Rational design and tuning of advanced sodium sulfide electrolytes needs a deep insight into the atomic structure and dynamics in relation with ion transport properties. Sodium fast ion conductors including glasses and glass ceramics are unparalleled materials for these applications. High-capacity solid-state batteries are promising future products for large-scale energy storage and conversion.

Furthermore, these Li-based complexions may facilitate the formation of dendrites and support short circuits in LLZO solid electrolytes. High frequency impedance spectroscopy revealed that the grain boundaries exhibit a lower conductivity and thus affect the Li-transport in LLZO. Interestingly, Li-based phases denoted as complexions (where Li is most probably found in an oxidized state) have been discovered at grain boundaries. Therefore, in the present work the grain boundaries in LLZO are investigated by atom probe tomography and correlative microscopy (combination of atom probe tomography with scanning electron microscopy) at the sub-nanometer level. This is because probing and quantifying lithium reliably remains difficult or sometimes even impossible with most microscopy techniques. However, it is not known to date if Li under its ionic state is enriched at grain boundaries of LLZO already during processing. It has been reported that metallic Li can accumulate at LLZO grain boundaries during operation, causing a short circuit and, hence, a failure of the battery. One of the key materials for all-solid-state batteries based on oxide electrolytes is the polycrystalline Li7La3Zr2O12 (LLZO).

Solid state battery