Accurate Measurements of Li⁺ Dynamics in Pressure-Treated Solid Electrolytes by Powder X-ray Diffraction and ⁷Li Magnetic Resonance Diffusometry

Applying fabrication pressure is an inevitable step when preparing solid electrolytes (SEs) for all-solid-state batteries (ASSBs). Utilizing Li-7 diffusometry and relaxometry nuclear magnetic resonance (NMR) measurements, this study demonstrates that the long-range ion transport in sulfide SEs, measured by diffusometry, is slowed by 20% following the application of pressure of 500 MPa. The local range relaxometry measurements show a more modest change. It is notable that the NMR and structural measurements are taken on samples after the applied pressure is removed, while the sample remains in the pellet form. The fact that this change in ion dynamics remains evident even when the pressure is no longer actively applied is an important finding that will impact the consideration of the role of pressure in altering the ion dynamics in ASSBs. Powder X-ray diffraction (PXRD) was performed on powder and compressed thiophosphate Li10SnP2S12 (LSnPS) samples to reveal the grain morphology change after pressure treatment. The PXRD analysis reveals the change in the peak shapes of the LSnPS materials, consistent with a significant microstrain imparted to the material by the fabrication pressure. A comparative investigation was performed for the reference ceramic oxide Li1.5Al0.5Ge1.5(PO4)(3) (LAGP) phase, where no significant changes were observed in either the ion dynamics or the micromorphology. This is expected due to the significantly larger Young's modulus of the oxide relative to that of the sulfide SEs. This study demonstrates the accuracy with which diffusometry and relaxometry NMR can measure changes in ion dynamics under mechanical modification, opening a new window to link macroscopic material engineering with particle-level dynamics and ion transport.