Molecular Interfacial Regulators Enable Stable Sulfide Electrolytes for High‐Performance All‐Solid‐State Batteries

ABSTRACT Interfacial instability remains a critical limitation for sulfide‐based solid electrolytes in all‐solid‐state batteries, where both reductive decomposition at lithium metal and oxidative degradation at high voltage hinder long‐term performance. Here, pyridine and fluorinated pyridine derivatives are introduced as molecular surface regulators for Li ₆ PS ₅ Cl ₀ . ₅ Br ₀ . ₅ (LPSClBr) argyrodite electrolytes. Among them, 3‐fluoropyridine exhibits the strongest interfacial binding via cooperative N–Li and F–Li interactions, effectively suppressing electronic conductivity while preserving fast ionic transport. As a result, the modified electrolyte delivers enhanced lithium compatibility, with an increased critical current density (3.1 vs 1.9 mA cm ^{− 2} ) and significantly improved Coulombic efficiency (98.5% vs 85.0%). At high voltage (up to 4.5 V), oxidative charge accumulation is reduced by over an order of magnitude in carbon composite cells, accompanied by suppressed interphase growth. These interfacial improvements translate into superior full‐cell performance with uncoated cathodes, achieving 90.6% capacity retention after 100 cycles compared to 64.8% for the pristine system. This work establishes molecular Lewis acid–base coordination as a scalable strategy to stabilize sulfide electrolytes across both reductive and oxidative regimes, offering a unified design principle for high‐performance solid‐state batteries.