Scalable High-Performance Li ₂ Zr 0.2 Ta 0.8 OCl 4.8 Solid Electrolytes: Structure, Dynamics, and Stability

High-performance solid electrolytes (SEs) are vital for advancing all-solid-state batteries (ASSBs) by improving safety, energy density, and longevity. While halide-based SEs offer excellent oxidative stability, further improvements in interfacial compatibility, ion transport, and efficient synthesis are still needed. Here, we introduce Li 2 Zr 0.2 Ta 0.8 OCl 4.8 (LZTOC), an amorphous oxychloride SE synthesized via a single-step, 2-hour mechanochemical process that eliminates high-temperature processing and hazardous byproducts, such as HCl gas. Structural characterization by XRD, Raman, and high-resolution NMR confirms an amorphous oxychloride framework with locally preserved Ta/Zr coordination motifs bridged by oxygen, thereby supporting a percolating ion-transport network. NMR relaxation measurements indicate enhanced Li + mobility relative to Li 2 ZrCl 6 and Li 2 ZrOCl 4 . Electrochemical measurements reveal a high ionic conductivity of 6.17 mS cm –1 and low activation energy ∼0.30 eV for LZTOC. Battery cycling tests with uncoated NMC811 as the cathode active material and LZTOC as the catholyte and separator deliver ∼88.9% capacity retention and an excellent Coulombic efficiency over 99.8% at extended cycles. These results position LZTOC as a scalable, high-performance oxychloride SE, where partial Zr-substitution improves cost-effectiveness relative to purely Ta-based analogues, for next-generation ASSBs.