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/LiFePO₄ and Li/IPE/LiNi_0.8Mn_0.1Co_0.1O₂ solid-state batteries also deliver high-capacity retentions of 95% and 97% at 0.2 C after 120 cycles, respectively.