LAUSR

Sodium storage batteries are one of the ever‐increasing next‐generation large‐scale energy storage systems owing to the abundant resources and low cost. However, their viability is severely hampered by dendrite‐related hazards on anodes. Herein, a novel ultrathin (8 µm) exterior‐nonporous separator composed of honeycomb‐structured fibers is prepared for homogeneous Na deposition and suppressed dendrite penetration. The unhindered ion transmission greatly benefits from honeycomb‐structured fibers with huge electrolyte uptake (376.7%) and the polymer's inherent transport ability. Additionally, polar polymer chains consisting of polyethersulfone and polyvinylidene customize the highly aggregated solvation structure of electrolytes via substantial solvent immobilization, facilitating ion‐conductivity‐enhanced inorganic‐rich solid‐electrolyte interphase with remarkable interface endurance. With the reliable mechanical strength of the separator, the assembled sodium‐ion full cell delivers significantly improved energy density and high safety, enabling stable operation under cutting and rolling. The as‐prepared separator can further be generalized to lithium‐based batteries for which apparent dendrite inhibition and cyclability are accessible and demonstrates its potential for practical application.