Trace Small Molecular/Nano-Colloidal Multiscale Electrolyte Additives Enable Ultra-Long Lifespan of Zinc Metal Anodes

Electrolyte additives are efficient to improve the performance of aqueous zinc-ion batteries (AZIBs), yet the current electrolyte additives are limited to fully water-soluble additives (FWAs) and water-insoluble additives (WIAs). Herein, trace slightly water-soluble additives (SWAs) of zinc acetylacetonate (ZAA) were introduced to aqueous ZnSO₄ electrolytes. The SWA system of ZAA is composed of a FWA part and a WIA part in a dynamic manner of dissolution equilibrium. The FWA part exists as soluble small molecules, which efficiently regulate Zn²⁺ ion solvation structure, while the WIA part exists as insoluble nano-colloids, which in-situ form a thick and robust solid electrolyte interface film on zinc metal anodes (ZMAs). Such small molecular/nano-colloidal multiscale electrolyte additives of ZAA are capable to not only improve ionic conductivity and transference number but also inhibit corrosion, hydrogen evolution, and Zn dendrite on ZMAs. The SWA-based Zn∥Zn half battery delivers a superb cumulative plating capacity of 15 Ah cm⁻² under 1 mAh cm⁻² and 20 mA cm⁻², and the SWA-based NH4V4O10∥Zn pouch cell obtains a capacity retention of 67.8% within 4000 cycles under 4 A g⁻¹. The study provides innovative insights for rational design of electrolyte additives, which may pave the way for the practicality of AZIBs.