A sustainable electrolyte towards dendrite-free and long-lasting zinc-metal batteries

Abstract Aqueous zinc (Zn) batteries hold great promise for large-scale energy storage by virtue of the high sustainability, low cost of Zn resources, high safety and low environmental impact. However, severe side reactions including Zn dendrite growth at the Zn surface hinder their practical application. “Water-in-salt” and organic/aqueous hybrid electrolytes address these problems but compromise the intrinsic merits of high ionic conductivity, superior safety, low cost and good sustainability. Herein, methylurea (MU) which has hydrogen (H) bond donor/acceptor properties is examined as a multifunctional electrolyte additive to boost the Zn anode reversibility without compromising the above advantages of aqueous electrolytes. Systematic experimental and theoretical analyses confirm that MU molecules alter the H-bonding network and reconstruct Zn 2+ solvation sheath; furthermore, the desolvation process can be facilitated with lower energy barriers. Besides, MU additives tend to be absorbed on the Zn surface to build a water-poor electrical double layer and can in-situ form a robust solid electrolyte interphase layer that protects the Zn anode. The Zn (002) plane is predominately deposited and can also be guided by MU. Consequently, the lifespan of the Zn||Zn cell using MU can maintain over 3000 h and the average Coulombic efficiency of the Zn||Cu cell reaches 99.7% throughout 1800 cycles. Additionally, our strategy can be applied in full cells with boosted performances for MnO 2 , activated carbon and conversion-type I 2 (capacity retention: 93.2% throughout 7500 cycles) cathodes under practical electrode ratios.