Boosting Ion Transport and Stability in Halide Solid Electrolytes via S and F Codoping

Structural and compositional modification of solid-state electrolytes (SSEs) is a common approach to improve ionic conductivity and interfacial stability, yet the mechanisms remain unclear. Here, we studied Li2ZrCl6 (LZC) codoped with sulfur (S) and fluorine (F). X-ray and neutron diffraction with bond valence site energy (BVSE) simulations reveal that codopant-induced lattice distortion facilitates ion transport. The S/F codoped sample achieves a room-temperature ionic conductivity of 0.51 mS cm–1, twice that of pristine LZC (0.26 mS cm–1). Advanced characterizations further show that S and F participate in forming the solid electrolyte interphase (SEI), enhancing the electrode interfacial stability. As a result, solid-state batteries with the codoped SSE deliver capacity retentions of 97.1% at 0.1 C and 82.8% at 0.5 C. This study demonstrates the synergistic effects of structural modulation on ionic conduction and SEI formation, providing insights for designing high-performance SSEs.