Zwitterionic Polymer Electrolytes With Dipole-Rotation-Assisted Ion Conduction for Solid Lithium Metal Batteries

Solid polymer electrolytes are promising for lithium metal batteries, yet achieving both high ionic conductivity and interfacial stability remains a major challenge. Here, we report a molecular rotor strategy that addresses this trade-off by incorporating 3-(1-Pyridinio)-1-propanesulfonate zwitterions (PP-Z) into a polyvinylidene difluoride electrolyte. This design establishes a dipole-rotation-assisted ion transport mechanism distinct from conventional polymer relaxation-dependent conduction. Molecular dynamics simulations and experiments reveal that the anchored cationic group of PP-Z serves as a pivot, while the mobile anionic end creates a dynamic coulombic field. This configuration facilitates rapid Li⁺ migration through coordinated intrachain transport and interchain hopping, significantly enhancing ionic conductivity (5.1 × 10^-4 S cm^-1 at 25°C and 1.5 × 10^-4 S cm^-1 at 0°C) and the Li⁺ transference number (0.52). The anionic terminals further participate in Li⁺ solvation and promote formation of a LiF-rich solid electrolyte interphase, enabling stable cycling for 1200 h in Li||Li cells at 0.3 mA cm^-2 and >  500 cycles in Li||LiFePO₄ cells at 1C (25°C). Even at 0°C, the Li||LiNi_0.8Co_0.1Mn_0.1O₂ (1.8 mAh cm^-2) pouch cell retains 85.1% capacity over 50 cycles while delivering 78.3% of its room-temperature capacity initially.