A Water-Repellent Ionic Liquid/MOF Protective Layer for Stable Zinc Anodes.

Aqueous zinc-ion batteries have emerged as promising candidates for large-scale energy storage, but their cycle stability is limited by irreversible zinc anodes due to dendrite growth and undesired side reactions. Here, an artificial composite protective layer consisting of a Zn metal-organic framework (MOF) layer infiltrated with a hydrophobic ionic liquid 1-ethyl-3-methylimidazoline bis(trifluoromethyl sulfonyl) imide is constructed on zinc anodes. The unique porous structure of the MOF enables uniform electric field distribution, effectively inducing uniform Zn plating and stripping. Meanwhile, a small amount of hydrophobic ionic liquid can effectively isolate the direct contact between the zinc anode and the aqueous electrolyte, thereby inhibiting undesired side reactions including hydrogen evolution reaction. In addition, the cations in the ionic liquid can act as a shielding layer to suppress the tip effect. Consequently, the stability of the zinc metal anode is greatly improved. The assembled symmetric cell is able to cycle stably for over 2600 h at 0.2 mA cm^-2/0.2 mAh cm^-2 and over 800 h at 1 mA cm^-2/1 mAh cm^-2, which also exhibits lower and more stable overpotentials.