Disentangling the Li-Ion transport and Boundary Phase Transition Processes in Li 10 GeP 2 S 12 Electrolyte by In-Operando High-Pressure and High-Resolution NMR Spectroscopy.

Li-ion transport and phase transition of solid electrolytes are critical and fundamental issues governing the rate and cycling performances of solid-state batteries. In this work, in-operando high-pressure nuclear magnetic resonance (NMR) spectroscopy for the solid-state battery is developed and applied, in combination with 6 Li-tracer NMR and high-resolution NMR spectroscopy, to investigate the Li 10 GeP 2 S 12 electrolyte under true-to-life operation conditions. The results reveal that the Li 10 GeP 2 S 12 phase may become more disordered and a large amount of conductive metastable β-Li 3 PS 4 as the glassy matrix in the electrolyte transforms into less conductive phases, mainly γ-Li 3 PS 4 , when high current densities (e.g., ≥0.5 mA cm -2 ) are applied to the electrolyte. The overall Li-transport also varies and shows a tendency of boundary phases and Li 10 GeP 2 S 12 synergistic dominant conduction at high currents. Accordingly, a mechanism of structural change induced by stress variation due to the drastic morphological change during Li-In alloying at high currents, and the local Li + diffusion coefficient discrepancy is proposed. These new findings of Li-ion transport and boundary phase transition in Li 10 GeP 2 S 12 solid electrolyte under high-pressure and high current density are first reported and will help provide previously lacking insights into the relationship of structure and performance of Li 10 GeP 2 S 12 .