New Oxyhalide Solid Electrolytes with Enhanced Conductivity for All-Solid-State Batteries

Departing from conventional Li– M –X 6 frameworks, we develop a Li– M –X 5 oxyhalide chemistry (Li 3 x TaO 3 x Cl 5–3 x, 0.8/3 ≤ x ≤ 1.4/3) to overcome the conductivity limitation of halide-based solid electrolytes (SEs). The designed oxyhalide achieves record ionic conductivities of 9 mS cm –1 at 30 °C and 0.59 mS cm –1 at −35 °C, surpassing most reported halides. Through comprehensive characterization using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), we confirm that oxygen incorporation reduces Ta–O/Ta–Cl coordination numbers and induces distorted O/Cl-containing polyhedra, collectively enhancing ion migration. Full ASSBs demonstrate excellent stable cycling with 100% capacity retention after long-term 3200 cycles at a substantial 4 C rate.