Isolation of Grain versus Intergranular Transport in Li_1+x Ti _x Ta_1-x SiO₅ Suggests Concerted Ion Migration in a High-Voltage Stable Electrolyte from High-Throughput Descriptors

LiTaSiO5, with its suitable conduction channels and wide electrochemical stability window, has been previously suggested as a potential host of concerted Li migration triggered by inserting Li interstitials. However, without proper separation of grain and grain boundary contributions, previous experimental efforts have been unable to isolate and quantitatively characterize the defect chemistry-conductivity relationship within the lattice. In this work, LiTaSiO5 was identified by descriptor filtering of the Materials Project database, and Li-i(center dot) were inserted via Ti-Ta ' doping to form Li1+xTixTa1-xSiO5. The grain and intergranular conductivities were separated using electrochemical impedance spectroscopy with distribution of relaxation times analysis (EIS/DRT). We showed the first clear observation of a monotonic decrease in activation energy E-A from 0.50 to 0.29 eV and a 6x increase in Li+ conductivity in the grains to 2.49 x 10(-5) S/cm for x = 0.15 (30 degrees C) as more Li-i(center dot) were inserted, providing insight into how Li-i(center dot) potentially triggered concerted transport. The necessity of separating grain and grain boundary contributions was further emphasized by observation, via STEM-EDS, of a Si-rich/Ta-poor intergranular amorphous phase that increases in volume with increasing Ti-Ta ' concentration. This phase led to a 19x increased specific grain boundary conductivity to 5.95 x 10(-6) S/cm for x = 0.15 (30 degrees C) with decreased E-A. The distribution of the intergranular phase was inhomogeneous (variation in size, stoichiometry), resulting in a wide distribution of relaxation times for the intergranular transport. Li1+xTixTa1-xSiO5 also exhibited wide electrochemical stability, up to 4.9 V, making it suitable for application as a solid electrolyte or cathode coating.