Abstract
Metallic zinc (Zn) is one of the most promising anodes for aqueous batteries, but so far its applicability for rechargeable systems remains elusive, mainly owing to the free water-induced parasitic reactions. Here, we report a new "water-in-deep eutectic solvent (water-in-DES)" electrolyte (similar to 30 mol.% H2O in a eutectic mixture of urea/LiTFSI/Zn(TFSI)(2); TFSI, bis(trifluoromethanesulfonyl) imide), in which all water molecules participate in DES's internal interaction (H-bonding and coordinating) network, leading to a suppressed reactivity with Zn anode from both thermodynamic and electrochemical aspects. Inheriting characteristics from aqueous and DES media, this electrolyte enables stable and reversible Zn plating/stripping with over twentyfold enhancement in cycling life compared to routine aqueous electrolytes, even at low rates. With these merits, a desirable rechargeability (> 90% capacity retention after 300 cycles at 0.1 C) is achieved for a 1.92 V (average dicharge voltage) Zn/LiMn2O4 battery, together with a practical energy density of 52 Wh/kg (pouch cell, 2 Ah, similar to 9.8 x excess Zn on anode).