Elucidating and Optimizing I Occupation in Lithium Argyrodite Solid Electrolytes for Advanced All‐Solid‐State Li Metal Batteries

Although iodine (I) doped Li₆PS₅Cl argyrodite sulfide electrolytes have attracted significant attention, a comprehensive understanding of how I^- occupancy influences ionic conductivity is still lacking. Herein, through ab initio molecular dynamics theoretical calculations, it was revealed that the incorporation of excess halogen at the sulfur site (4d) significantly accelerates the inter-cage jumps of Li⁺ with a low migration energy barrier of 0.28 eV, enhancing the ionic diffusion kinetics. Subsequently, iodine-rich Li_6- <i>_x</i> PS_5- <i>_x</i> ClI_x (0 ≤ <i>x</i> ≤ 0.2) electrolytes are successfully synthesized and deliver high ionic conductivity. Moreover, a stable Li/Li_6- <i>_x</i> PS_5- <i>_x</i> ClI <i>_x</i> interface is achieved to inhibit side reactions and lithium dendrite growth. Therefore, Li symmetric cells with the optimized electrolyte present splendid cyclic stability (7000 h at 0.1 mAh cm^-2 and 1500 h at 0.5 mAh cm^-2). The constructed full cells with optimized electrolytes exhibit excellent electrochemical properties at a broad temperature range and with different active materials. This work deepens the understanding of the relationship between ion transport and structure in lithium argyrodite sulfide electrolytes.