Na+-Enriched Quinoid Polymer Layer with Fast Ion Transport for Dendrite-Free Sodium Metal Batteries with High Cyclic Stability

An unstable solid electrolyte interphase (SEI) layer on a metal electrode leads to issues of severe dendrite formation and side reactions, resulting in low cycle stability and safety hazards of metal-based batteries. Herein, a functional quinoid polymer (poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene), PDBM) is introduced on the surface of Na/Li metal, forming a flexible and uniform polymer–salt (PDBM-Na/Li)-based SEI with Na+/Li+ enriching property and low ion dissociation energy. The PDBM-Na layer enables a stable Na plating/stripping behavior with over 1200 h cycles at 2 mA cm–2 and Na∥Na3V2(PO4)3 full batteries with a capacity retention of 93% after 2400 cycles at 5 C. Equally important, a comparison study of PDBM-Na/Li layers on the cycling stability of Na/Li metals demonstrates that not only an appropriate ion adsorption energy but also a low dissociation energy is important for extending the cyclic lifespan of metal electrodes. This study provides deep insights into the structural design of functional polymers for alkaline anode protection.