Three Birds with One Stone: Tetramethylurea as Electrolyte Additive for Highly Reversible Zn-Metal Anode

Aqueous Zn-metal batteries are the most promising system for large-scale energy storage due to their high capacity, high safety, and low cost. The Zn-metal anode, however, suffers from continuous parasitic reactions, random dendrite growth, and sluggish kinetics in aqueous electrolytes. Herein, a high donor number solvent, tetramethylurea (TMU), is introduced as electrolyte additive to enable highly reversible Zn-metal anode, where the TMU can 1) preferentially adsorb on the Zn surface to inhibit Zn corrosion and suppress parasitic reaction, 2) solvate with Zn2+ and exclude the H2O from Zn2+ solvation sheath to weaken water activity significantly, and 3) contribute to form an inorganic-organic bilayer solid electrolyte interphase to enable homogeneous and rapid Zn2+ transport kinetic for dendrite-free Zn deposition. Benefiting from these three merits, the resulting aqueous electrolyte demonstrates a highly reversible Zn plating/stripping cycling in a Zn||Ti asymmetric cell for over 1200 cycles and in a Zn||Zn symmetric cell for over 4000 h. As a proof-of-concept, the aqueous Zn-metal full cells assembled with various state-of-the-art cathodes also deliver excellent cycling performance even with a 10 mu m thin Zn anode, favoring the practical application.