Exploring dopant-enhanced ionic conductivity of AgCl-doped Li₇P₃S₁₁ solid electrolytes: Integrating synchrotron Rietveld analysis, DFT, and ANN-based molecular dynamics approaches

The effectiveness of dual-doping as a method of improving the conductivity of sulfide solid electrolytes (SEs) is not in doubt; however, the atomic-level mechanisms underpinning these enhancements remain elusive. In this study, we investigate the atomic mechanisms associated with the high ionic conductivity of the Li₇P₃S₁₁ (LPS) SE and its response to Ag/Cl dual dopants. Synthesis and electrochemical characterizations show that the 0.2 M AgCl-doped LPS (Li_6.8P₃Ag_0.1S_10.9Cl_0.1) exhibited an over 80% improvement in ionic conductivity compared with the undoped LPS. The atomic-level structures responsible for the enhanced conductivity were generated by a set of experiment and simulation techniques: synchrotron X-ray diffractometry, Rietveld refinement, density functional theory, and artificial neural network-based molecular dynamics simulations. This thorough characterization highlights the role of dual dopants in altering the structure and ionic conductivity. We found that the PS₄ and P₂S₇ structural motifs of LPS undergo transformation into various PS_x substructures. These changes in the substructures, in conjunction with the paddle-wheel effect, enable rapid Li migration. The dopant atoms serve to enhance the flexibility of PS₄–P₂S₇ polyhedral frameworks, consequently enhancing the ionic conductivity. Our study elucidates a clear structure–conductivity relationship for the dual-doped LPS, providing a fundamental guideline for the development of sulfide SEs with superior conductivity.