Harnessing Metal Ion-Tannic Acid Complexes to Engineer an Artificial SEI for Ultra-Stable Zinc Metal Batteries

A facile and efficient method for preparing a protective layer on the Zn anode is highly desirable in rechargeable aqueous zinc metal batteries. This coating layer should meet the requirements for suppressing dendritic Zn proliferation and inhibiting parasitic side reactions. We engineer an artificial SEI composed of a metal ion-tannic acid (TA) complex on the Zn anode. The synergistic effect of TA and metal ions enables a dual confinement mechanism with abundant zincophilic sites, thereby enhancing the ability to capture Zn ions and facilitating rapid ion transfer. This complex layer can suppress the hydrogen evolution reaction and have anticorrosion properties. Theoretical calculations demonstrate that the protective coating exhibits a high affinity for Zn2+, significantly reducing the nucleation barrier. Furthermore, it regulates Zn²⁺ flux to enhance uniform Zn deposition and restrain dendritic growth. As a result, Zn symmetric cells using the metal ion-TA complex coating exhibit exceptional stability and a lifespan of 2300 h at 1 mA cm^-2/1 mAh cm^-2, significantly exceeding that of pristine Zn. Furthermore, coupled with a vanadium-based cathode, the cell retains ∼100% of its initial specific capacity (176.75 mAh g^-1) at 5 A g^-1 through 2500 cycles without observable degradation. This work proposes a promising method for protecting Zn metal anodes with a large-scale implementation potential.