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

Abstract 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//LiFePO 4 and Na//Na 3 V 2 (PO 4 ) 2 F 3 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.