Liquid-like solid-state diffusion of lithium ions in super-halide-rich argyrodite
Yübo Wang, David Bazak, Laidong Zhou, Qiang Zhang, Baltej Singh, Linda F. Nazar
Abstract
The development of solid electrolytes with high ionic conductivity is essential for advancing safer, high-energy-density solid-state batteries, where lithium site distribution in the sublattice strongly affects ion transport. Here, we report a super-halide-rich argyrodite, Li<sub>5.3</sub>PS<sub>4.3</sub>Cl<sub>1.7</sub>, with remarkable room-temperature ionic conductivity (11.4 ± 0.7 mS cm<sup>-1</sup>) due to population of two additional interstitial lithium sites induced by vacancy redistribution. Prominent lithium density between lithium sites and elevated atomic displacement parameters indicate liquid-like diffusive behavior resembling sublattice melting. Combining electrochemical impedance spectroscopy, pulsed-field gradient NMR, and T<sub>1</sub> relaxation methods, we demonstrate that the augmented conductivity partly arises from a low energy barrier (0.08 eV) at the local scale, attributed to a three-site lithium distribution that drives correlated lithium dynamics. This work advances our understanding of the structure-dynamics interplay in super-halide-rich argyrodites, and highlighting their potential as solid-state battery electrolytes in cells with a coated single-crystal NMC82 cathode that achieve 170 mAh/g capacity at a 0.2 C rate .