<scp>Electronegativity‐Induced Single‐Ion</scp> Conducting Polymer Electrolyte for <scp>Solid‐State</scp> Lithium Batteries

The application of solid polymer electrolytes (SPEs) is severely impeded by the insufficient ionic conductivity and low Li+ transference numbers (tLi+). Here, we report an iodine-driven strategy to address both two long-standing issues SPEs simultaneously. Electronegative iodine-containing groups introduced on chains effectively attract ions, facilitate transport, promote dissociation Li salts. Meanwhile, iodine also favorable alleviate strong O−Li+ coordination through a Lewis acid–base interaction, further improving tLi+. As proof concept, iodinated single-ion conducting electrolyte (IPE) demonstrates high 0.93 mS cm−1 tLi+ 0.86 at 25 °C, which among best results ever reported for SPEs. Moreover, symmetric Li/Li cells with IPE achieve long-term stability over 2600 h in-situ formed LiF-rich interphase. result, Li−S battery maintains capacity 623.7 mAh g−1 300 cycles average Coulombic efficiency 99%. When matched intercalation cathode chemistries, Li/IPE/LiFePO4 Li/IPE/LiNi0.8Mn0.1Co0.1O2 solid-state batteries deliver high-capacity retentions 95% 97% 0.2 C after 120 cycles, respectively.