Unveiling a Stable Polysulfide Transport Framework in a Fluorine-Free Li-S Batteries

Lithium-sulfur batteries are limited by severe polysulfide shuttling, unstable lithium interfaces, and parasitic redox reactions, which degrade cycle life and efficiency. These issues stem from the soluble nature of polysulfide intermediates and the poor interfacial control in conventional electrolytes. Herein, we report a fluorine-free phosphate-based electrolyte that fundamentally shifts the redox chemistry from the typical S₈-Li₂S pathway to a reversible Li₃PS₄-Li₂S mechanism. This in situ transformation produces Li-rich thiophosphate phases that suppress polysulfide diffusion, alleviate cathode expansion, and promote solid-state-like behavior. Spectroscopic and microscopic analyses revealed dynamic phase transitions within the Li-P-S complexes that drive reversible conversion and sustained performance. As a result, the cells delivered a stable capacity of 765 mAh g^-1 over 200 cycles. This work presents a fluorine-free electrolyte design that establishes a new class of solid-state-like Li-S redox chemistry, offering a promising route toward durable, high-performance lithium-sulfur batteries.