Constructing organic−inorganic−gradient hybrid SEI on zinc anode for long−life zinc metal batteries

Zinc anodes suffer from dendrite growth and side reactions, limiting Coulombic efficiency (CE) and cycling stability. Constructing a stable solid electrolyte interphase (SEI) is critical, yet the electrolyte structure–SEI relationship remains unclear. Here, we introduce tetraethylene glycol dimethyl ether (TEGDME) into aqueous Zn(OTf) 2 electrolyte. Unlike conventional additives, TEGDME does not enter the primary Zn(H₂O)₆²⁺ solvation shell but alters the secondary solvation shell, disrupting hydrogen bonding and facilitating solvent−separated ion pairs (SSIPs, e.g., Zn 2 + –H 2 O–OTf⁻). This creates an “organic–inorganic hybrid” solvation structure, leading to a gradient hybrid SEI with a ZnF₂−rich outer layer and an inner layer enriched in organic species, ZnS, and ZnCO 3 . This SEI enables dendrite−free Zn deposition and suppresses side reactions. Consequently, the Zn||Cu cell achieves 99.76% CE, the Zn||Zn symmetric cell cycles for 2400 h, and the Zn||VOH full cell retains 80% capacity after 1100 cycles, far outperforming the unmodified electrolyte.