Anion-tethered Single Lithium-ion Conducting Polyelectrolytes through UV-induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

Single Li⁺ ion conducting polyelectrolytes (SICs), which feature covalently tethered counter-anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li⁰ ) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single-step UV polymerization approach. The resulting electrolyte exhibited a high Li⁺ transference number (t₊ ) of 0.85 and demonstrated good Li⁺ conductivity (6.3×10^-5  S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10^-5  S/cm). Benefitting from the high transference number of SIC, it displayed a three-fold higher critical current density (2.4 mA/cm² ) compared to DIC (0.8 mA/cm² ) by successfully suppressing concentration polarization-induced short-circuiting. Additionally, the t₊ significantly influenced the deposition behavior of Li⁰ , with SIC yielding a uniform, compact, and mosaic-like morphology, while the low t₊ DIC resulted in a porous morphology with Li⁰ whiskers. Using the SIC electrolyte, Li⁰ ||LiFePO₄ cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.