Anion Chemistry towards On-Site Construction of Solid-Electrolyte Interface for Highly Stable Metallic Zn Anode.

Reversibility of metallic Zn anode serves as the corner stone for the development of aqueous Zn metal battery, which motivates scrutinizing the electrolyte-Zn interface. As the representative organic zinc salt, zinc trifluorosulfonate (Zn(OTf)) facilitates a broad class of aqueous electrolytes, however, the stability issue of Zn anode remains crucial. The great challenge lies in the lack of Zn anode protection by the pristinely formed surface structure in aqueous Zn(OTf) electrolytes. Accordingly, an electrochemical route was developed to grow a uniform zinc trifluorosulfonate hydroxide (ZTH) layer on Zn anode as an artificial SEI, via regulation on metal dissolution and strong coordination ability of zinc ions. Co-precipitation was proposed to be the formation mechanism for the artificial SEI, where the reduction stability of OTf anion and the low-symmetry layer structure of ZTH was unmasked. This artificial SEI favors interfacial kinetics, depresses side reactions, and well maintains its integrity during cycling, leading to a prolonged lifespan of Zn stripping/plating with a high DOD of ~85 %, and an improved cycling stability of ~92 % retention rate for VO/Zn cell at 1 A g. The unveiled role of anion on Zn anode drives the contemplation on the surface chemistry for the blooming aqueous rechargeable battery.