Electronegativity‐Induced Single‐Ion Conducting Polymer Electrolyte for Solid‐State Lithium Batteries

The application of solid polymer electrolytes (SPEs) is severely impeded by the insufficient ionic conductivity and low Li + transference numbers ( t Li + ). Here, we report an iodine‐driven strategy to address both the two long‐standing issues of SPEs simultaneously. Electronegative iodine‐containing groups introduced on polymer chains effectively attract Li + ions, facilitate Li + transport, and promote the dissociation of Li salts. Meanwhile, iodine is also favorable to alleviate the strong O−Li + coordination through a Lewis acid–base interaction, further improving the ionic conductivity and t Li + . As a proof of concept, an iodinated single‐ion conducting polymer electrolyte (IPE) demonstrates a high ionic conductivity of 0.93 mS cm −1 and a high t Li + of 0.86 at 25 °C, which is among the best results ever reported for SPEs. Moreover, symmetric Li/Li cells with IPE achieve a long‐term stability over 2600 h through the in‐situ formed LiF‐rich interphase. As a result, Li−S battery with IPE maintains a high capacity of 623.7 mAh g −1 over 300 cycles with an average Coulombic efficiency of 99%. When matched with intercalation cathode chemistries, Li/IPE/LiFePO 4 and Li/IPE/LiNi 0.8 Mn 0.1 Co 0.1 O 2 solid‐state batteries also deliver high‐capacity retentions of 95% and 97% at 0.2 C after 120 cycles, respectively.