Intermediate-Phase Blocking as a Kinetic Lever for High Ionic Conductivity of Wet-Synthesized Cl-Rich Li Argyrodite for All-Solid-State Batteries

Achieving high ionic conductivity of wet-synthesized sulfide solid electrolytes remains a critical challenge for enabling scalable all-solid-state batteries (ASSBs). In Cl-rich Li-argyrodites, Li⁺ transport is strongly governed by the Cl occupancy at the 4d Wyckoff site, yet conventional wet syntheses fail to control this local structure due to the spontaneous formation of unfavorable intermediate phases. Here, we uncover that the formation of the PS₃Cl^2- moiety during intermediate heat-treatment stages suppresses 4d-site Cl incorporation, thereby limiting ionic conductivity. By introducing controlled amounts of S₈ as a reaction-kinetic modulator, we show that S-S-containing precursor environments kinetically hinder PS₃Cl^2- formation during heat treatment. Multimodal structural analyses (solid-state NMR, XRD Rietveld refinement, DSC) confirm that increasing S₈ systematically increases 4d-site Cl occupancy while suppressing the undesired intermediate. This kinetic steering enables the Li_5.5PS_4.5Cl_1.5 (LPSCl_1.5) electrolyte to reach a high ionic conductivity of 6.06 ± 0.29 mS cm^-1 at 25°C without additional specialized processing such as rapid thermal annealing or spark plasma sintering. ASSB half-cells incorporating this electrolyte exhibit excellent rate capability and 77.8% capacity retention over 500 cycles at 2 C. This work establishes a mechanistic framework for intermediate-phase engineering in wet synthesis and presents a high-performance wet-synthesis route with potential for scale-up.