Innovative Design of a Double-Layer Gradient Coating for Dendrite-Free and Ultrastable Zinc Anodes.

The rampant "top-growth" dendrites, hydrogen evolution reaction (HER), and zinc (Zn) self-corrosion severely impede the further development of rechargeable aqueous zinc ion batteries. To address these challenges, a novel double-layer gradient coating consisting of a zincophilic Sn inner layer and an organic polymer outer layer (OSA/PAM@Sn) is constructed on the surface of the Zn anode. The organic outer layer, composed of cross-linked oxidized sodium alginate and polyacrylamide (OSA/PAM), not only serves as a physical barrier to isolate active water but also accelerates Zn diffusion by facilitating the desolvation process of [Zn(HO)] due to its plentiful polar functional groups, thereby effectively suppressing the detrimental HER and Zn self-corrosion. Simultaneously, the loose Sn inner layer can offer abundant nucleation sites to induce uniform "bottom-to-top" Zn deposition with low overpotential. Benefiting from the synergistic effect of the designed double-layer gradient coating, the OSA/PAM@Sn-Zn anode exhibits remarkable reversibility, with lifespans of over 5000 and 1200 h at 1 mA cm-1 mAh cm and 5 mA cm-5 mAh cm in symmetric cells, respectively. Additionally, the MnO||OSA/PAM@Sn-Zn full battery also displays an improved rate performance and cycle stability. This work emphasizes the importance of synergistic effects in interface design to achieve side reaction-free and dendrite-free Zn anodes.