Lithium argyrodite thiophosphate superionic conductors are being explored as promising solid electrolytes for all-solid-state batteries, primarily due to their high ionic conductivity and ease of processing. Yet, these electrolytes present challenges such as chemical instability in humid conditions and incompatibility with cathode materials. Although some lithium argyrodites show improved air stability, their ionic conductivity deteriorates below the practically required value. Herein, based on hard soft acid base theory, a new family of lithium argyrodite, as solid solution Li6−xAsS5−xBr1+x (for 0.0 ≤ x ≤ 0.6), has been proposed to address these issues. Through a combination of neutron diffraction, NMR spectroscopy, and electrochemical impedance spectroscopy, it has been determined that the partial substitution of S2− by Br− weakens interactions within the Li+ “cage”, facilitating long lithium-ion movement throughout the structure. An additional T4 Li+ site is identified, offering a lower energy barrier for inter-cage jumps. Consequently, the Li5.5AsS4.5Br1.5 member of the composition series exhibits a higher Li-ion diffusivity resulting in a remarkable ionic conductivity of 15.4 mS cm−1. Compared with lithium thiophosphates, the Li5.5AsS4.5Br1.5 also shows excellent air stability. This research opens a new avenue for developing air-stable sulfide solid electrolytes with high ionic conductivity necessitated for practical application in solid-state batteries.

Lithium argyrodites with high ionic conductivities are favorable solid electrolytes (SEs) for all-solid-state batteries (ASSBs). However, their low preparation efficiency and poor cycling performance hinder their large-scale applications. In this work, we demonstrate successful large-scale production (over 1 kg per batch for the first time) of Li_5.5PS_4.5Cl_0.75Br_0.75 (LPSCB) by fast dry mixing followed by annealing, which presents high room temperature ionic conductivities of 13 mS cm⁻¹ for cold-pressed and 25 mS cm⁻¹ for sintered pellets. Combining neutron powder diffraction and ⁶Li → ⁷Li tracer-exchange nuclear magnetic resonance (NMR) spectroscopy measurements, we show that intercage jumps frequently occur through the 48h-16e-48h pathway in LPSCB, promoting the overall lithium conduction. The assembled ASSBs using LPSCB and a LiNi_0.83Co_0.11Mn_0.06O₂ electrode can be cycled for over 2,500 cycles at a 0.5 C rate and 1,800 cycles at a 2 C rate without any capacity degradation. Our results will accelerate the commercialization of sulfide SE for ASSBs.

Lithium argyrodite solid electrolytes have attracted ever-increasing attention for all-solid-state batteries due to their high ionic conductivity and low cost. However, the relation between structure and ionic transport for the halogen-rich lithium argyrodites under different synthesis routes is still elusive. Herein, the influence of synthesis procedures, such as annealing conditions and balling milling, on the structure, ionic conductivity, and activation energy of the lithium argyrodite (e.g., Li_5.5PS_4.5Cl_1.5, Li_5.3PS_4.3Cl_1.7), is systematically investigated. Compared with high-energy ball milling followed by annealing, using fast dry mixing followed by annealing can obtain comparable ionic conductivity of the chlorine-rich lithium argyrodites. Single-crystal LiNi_0.83Co_0.11Mn_0.06O₂-based solid-state battery with these electrolytes shows stable cycling performance, demonstrating that chlorine-rich lithium argyrodite is a promising candidate for all-solid-state batteries.