Disentangling the Li‐Ion transport and Boundary Phase Transition Processes in Li10GeP2S12 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 Li₁₀ GeP₂ S₁₂ electrolyte under true-to-life operation conditions. The results reveal that the Li₁₀ GeP₂ S₁₂ phase may become more disordered and a large amount of conductive metastable β-Li₃ PS₄ as the glassy matrix in the electrolyte transforms into less conductive phases, mainly γ-Li₃ PS₄ , 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 Li₁₀ GeP₂ S₁₂ 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 Li₁₀ GeP₂ S₁₂ 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 Li₁₀ GeP₂ S₁₂ .