Comparative study of oxygen source doping effects on the multidimensional stability of Li5.5PS4.5Cl1.5 solid electrolytes

Abstract

The Cl-rich argyrodite, Li_5.5PS_4.5Cl_1.5, has emerged as a promising solid electrolyte candidate due to its high ionic conductivity and good Li metal compatibility. However, its practical application is significantly limited by poor air stability. In this work, we systematically investigate two oxygen doping strategies (Li₂O vs. P₂O₅ substitution) to enhance the moisture resistance of Li_5.5PS_4.5Cl_1.5 while maintaining its advantageous ionic transport properties. Our results reveal distinct effects of different doping sources: the Li₂O-doped electrolyte achieves superior room-temperature ionic conductivity (8.4 mS cm⁻¹), while the P₂O₅-doped sample demonstrates remarkable air stability with well-preserved structural integrity and conductivity after air exposure. Through combined DFT calculations and experimental characterization (XRD, SEM), we elucidate that P₂O₅-doping induces larger cell parameters and stronger structural robustness against moisture attack. When implemented in all-solid-state batteries using ZrO₂-coated LiNi_0.9Mn_0.05Co_0.05O₂ cathodes and Li–In anodes, the exposed P₂O₅-doped electrolytes exhibited higher discharge capacity and promising interface compatibility, further confirming its better air stability. Further investigation using a bilayer electrolyte configuration with Li_3.25InCl_5.75O_0.25 confirms the excellent compatibility of P₂O₅-LPSC, which achieves a high initial discharge capacity of 230.7 mAh g⁻¹ and maintains 87.1% capacity retention after 200 cycles. Electrochemical impedance spectroscopy revealed that P₂O₅-LPSC forms more favorable interfaces with halide electrolytes, contributing to its outstanding cycling stability. This work provides fundamental insights into designing air-stable, high-performance solid electrolytes through rational doping strategies.