All-solid-state batteries as an emerging electrochemical energy storage technology are attracting extensive attentions, owing to the good safety properties and potentially very high energy density with using Li-metal anode. Solid electrolyte (SE) is the key component in all-solid-state Li-ion batteries and solid state Li ion conductors with high room temperature conductivity, ideal electrochemical stability and good mechanical compatibility are very much desired. Oxides and sulfides based SEs have their own advantages and disadvantages. Oxides can be handled and stored in ambient environment, while their room temperature ionic conductivity is relatively low and the grain boundary is high. Sulfides are commonly not very stable with air and moisture, but they have much higher ionic conductivity, lower grain boundary resistance and favorable mechanical properties for cold processing of solid cells.

Here we report recent progresses in our research group in both oxide and sulfide-based lithium ion conductors. A group of zirconia doped lithium tantalum oxosilicate previously identified through a computation assisted search and screening were successfully synthesized and showed encouraging ionic conductivity of >10^-5 S/cm at room temperature. Analysis of electrochemical impedance spectroscopy data and computation predictions indicate that higher conductivity from 10^-4 to 10^-3 S/cm may be achieved by further optimizations. With using another experiment-based design strategy, a group of lithium chloro-thiophosphate compounds were also experimentally identified assisted by in situ X-ray diffraction investigations and showed high conductivity of >10^-4 S/cm. The structure of both sulfide and oxide new compounds were characterized with using synchrotron X-ray diffraction and neutron diffraction. The relationship between their ionic conductivity and structural features, such as unit cell size, diffusion pathway, site occupancy, interstitial sites, etc., were revealed by the characterization and will be discussed in the presentation.

Caption of Figure 1. a) Crystal structure and ionic conductivity of Zr doped LiTaSiO₅ with sphene structure. b) Crystal structure of new lithium chloro-thiophosphate