Unravelling Li-Ion Transport from Picoseconds to Seconds

Abstract

One of the main challenges of all-solid-state Li-ion batteries is the restricted power density due to the poor Li-ion transport between the electrodes via the electrolyte. However, to establish what diffusional process is the bottleneck for Li-ion transport requires the ability to distinguish the various processes. The present work investigates the Li-ion diffusion in argyrodite Li₆PS₅Cl, a promising electrolyte based on its high Li-ion conductivity, using a combination of ⁷Li NMR experiments and DFT based molecular dynamics simulations. This allows us to distinguish the local Li-ion mobility from the long-range Li-ion motional process, quantifying both and giving a coherent and consistent picture of the bulk diffusion in Li₆PS₅Cl. NMR exchange experiments are used to unambiguously characterize Li-ion transport over the solid electrolyte-electrode interface for the electrolyte-electrode combination Li₆PS₅Cl-Li₂S, giving unprecedented and direct quantitative insight into the impact of the interface on Li-ion charge transport in all-solid-state batteries. The limited Li-ion transport over the Li₆PS₅Cl-Li₂S interface, orders of magnitude smaller compared with that in the bulk Li₆PS₅Cl, appears to be the bottleneck for the performance of the Li₆PS₅Cl-Li₂S battery, quantifying one of the major challenges toward improved performance of all-solid-state batteries.