High-viscoelasticity alginate-based coatings for reversible zinc metal anodes.

High-safety aqueous zinc (Zn) ion batteries are troubled by dendrite growth and hydrogen evolution reaction on Zn anode, which can be well solved via the construction of surface protective layer. The recent researches mainly focus on the bulk property of the protective layer, but its separation from Zn anode is ignored. In this work, high-viscoelasticity alginate-based (HVAA) layer was in-situ constructed on Zn anodes by the cross-linking of sodium alginate with formaldehyde and the plastifying of glycerin. HVAA layer can combine with HO and coordinate with Zn ions in aqueous electrolyte to achieve viscoelasticity on Zn anode, which can accommodate volume change of Zn anode during plating/stripping processes to continuously protect Zn anodes under the real battery system. Physical block effect of HVAA layer impedes hydrogen evolution corrosion reaction by avoiding the immediate contact of Zn anodes with aqueous electrolyte. Ionic conductive ability of HVAA layer by coordinating oxygen-containing groups with Zn can uniform ion flux to induce the homogeneous deposition of Zn on Zn anode. Zn anode with HVAA endows ZnZn symmetric battery with stably cycle of 4000 h and Zn-iodide full batteries with better electrochemical performance of 8000 cycles comparing with bare Zn anode. This work opens a novel route to continuously protect Zn anode through the high-viscoelasticity films to closely fit with Zn surface and implement the high-value application of renewable sources.