Ion Flux Regulation through PTFE Nanospheres Impregnated in Glass Fiber Separators for Long-Lived Lithium and Sodium Metal Batteries

Practical implementation of alkali metal batteries currently still faces formidable challenges because of the dendrite growth upon continuous charge/discharge processes and the associated unstable solid–electrolyte interphase. Herein, it is reported that dendrites can be fundamentally mitigated in lithium and sodium metal batteries by regulating the Li⁺ and Na⁺ flux using a glass fiber (GF) separator impregnated with polytetrafluoroethylene nanospheres (PTFE-NSs), which results in homogeneous deposition of Li and Na during charging. The COMSOL Multiphysics simulations reveal that the introduction of negatively charged PTFE-NSs into the GF separator enhances the local electric field near the anode, thereby boosting the transfer of cations. It is demonstrated that Li//Li and Na//Na symmetric cells utilising a PTFE-GF separator show outstanding cycle stability of 1245 and 2750 h, respectively, at 0.5 mA cm⁻². Moreover, the Li//LiFePO₄ and Na//Na₃V₂(PO₄)₂F₃ full cells exhibit remarkably improved capacity retention when cycled at 1 C, in the presence of a PTFE-GF separator. The nuclear magnetic resonance spectroscopy studies suggest that the impregnation of PTFE-NSs into GF helps “liberate” more Li⁺ and Na⁺ and changes the coordination interaction between ions and solvents, contributing to the enhanced electrochemical performance.