Functional Separator Induced Interface Potential Uniform Reformation Enabling Dendrite‐Free Metal Batteries

Abstract Uncontrolled dendrite growth leads to poor cycling performance and potential safety hazards in high‐energy metal resource‐rich (Na/Mg) batteries. Herein, a polar Nylon 6‐cellulose acetate (NCA) separator is designed to regulate electrolyte solvation structure and electrode–electrolyte interface potential for dendrite‐free Na/Mg batteries. The different dipole interactions between separator's groups (CONH, COOR, ROR, OH) and anhydride/ether groups from ester/ether solvents ensure the universality in various electrolytes. In sodium batteries, the groups‐constructed confined space within NCA separator exhibits competitive coordinate with ethylene carbonate‐EC, diethyl carbonate‐DEC, fluoroethylene carbonate‐FEC, which induces an anion‐dominated Na + solvation structure (NCA: CN solvent ‐3.83, polypropylene: CN solvent ‐6.47). Then, the induced concentration‐enhanced PF 6 − derives NaF‐rich solid electrolyte interphase with high electronic insulation, against dendrite growth owing to electronic leakage. Moreover, the homogeneous potential distribution caused by electronic cloud overlap (δ O − ↔ δ H + ) between NCA separator and EC/DEC/FEC enables fast and well‐distributed Na deposition. Furthermore, the phase‐field simulations via COMSOL reveal that the enhanced diffusion flux (1.59 mol m −2 s −1 ) fundamentally inhibits Na dendrite nucleation. Electrochemical tests show that NCA separator facilitates the stable Na||NFPP cell (96.3%, 1,600 cycles, 10 C). Additionally, the NCA separator can be employed to govern 0.4 m (PhMgCl) 2 ‐AlCl 3 THF electrolyte, achieving homogeneous Mg deposition.