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 PF₆⁻ 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-AlCl₃ THF electrolyte, achieving homogeneous Mg deposition.