In-situ construction of a hydroxide-based solid electrolyte interphase for robust zinc anodes

Zinc (Zn) metal anode in conventional aqueous electrolytes suffers from water-induced side reactions (hydrogen evolution reaction (HER) and corrosion) and dendrite growth due to the absence of a reliable solid electrolyte interphase (SEI) layer. Here, a robust and Zn2+-conducting SEI composed of zinc hydroxide sulfate hydrate (ZHS) on Zn has been built in-situ by introducing SO42- additives (e.g., ZnSO4 or Na2SO4 salt) into a non-concentrated aqueous electrolyte (i.e., 2 M zinc trifluoromethanesulfonate (Zn(OTF)2)). Comprehensive characterizations demonstrate that the in-situ formation of SEI with compact structure is induced by a self-terminated chemical reaction of SO42- with Zn2+ and OH– (stemming from HER) during the initial cycles, which in-turn terminates the continuous HER and Zn corrosion by isolating Zn from the bulk electrolyte and simultaneously allows a homogeneous Zn2+ diffusion. As a result, the in-situ formed SEI enables a high reversibility of Zn//Cu cell (99.8% Coulombic efficiency over 600 cycles at 1.0 mA cm−2) and an unprecedented cycling life of Zn//Zn cell (over 2000 h at 1.0 mA cm−2), and contributes to a stable operation of Zn//V2O5·nH2O full battery. This work will guide the interface engineering to build reliable SEI on metal anodes for aqueous batteries.