Trimethylolethane-mediated electric double layer engineering for dendrite-free zinc anodes

Electrolyte additives are a key strategy for stabilizing zinc anodes and interfaces in aqueous zinc ion batteries (AZIBs). However, conventional additives often affect both the electric double layer (EDL) and the solvated sheath of Zn²⁺, resulting in ambiguous mechanistic interpretations. Here, we introduce trimethylolethane (TME) as an additive that selectively modifies the EDL architecture without altering the Zn²⁺ solvation structure, enabling precise elucidation of EDL-mediated anode stabilization. TME preferentially adsorbs onto the zinc anode surface over water molecules, enabling dual-functional regulation: it reduces Zn²⁺ adsorption on the Zn (101) crystal facet while enhancing adsorption on the Zn (002) facet, thereby promoting uniform Zn²⁺ distribution. More importantly, TME molecules penetrate the EDL to form a stable, water-deficient interface, reducing active H₂O molecules and suppressing parasitic reactions. Concurrently, the EDL-embedded TME increases zinc ion nucleation overpotential, creating abundant nucleation sites and promoting the formation of compact, dendrite-free Zn deposits. The Zn||Zn symmetric cell with TME additive remarkably achieved a cycle life of up to 1495 h at 1 mA cm⁻² (1 mAh cm⁻²), outperforming most reported electrolyte systems. This work establishes a new paradigm in EDL-oriented electrolyte engineering, providing critical insights for the rational design of next-generation high-performance AZIBs.