Comprehensive protection of Zn metal anode via caprolactam towards highly stable aqueous zinc ions batteries

Rampant side reactions such as hydrogen evolution reaction (HER), corrosion and uncontrollable dendrite growth at anodes greatly impede the application of AZIBs. Herein, caprolactam (CPL) is employed as a crucial electrolyte medium to achieve the aim of highly reversible zinc anodes. CPL molecules exhibit a lower adsorption energy (-1.94 eV) than H2O and preferential binding with Zn anodes, resulting in a H2O-poor anode/electrolyte interface and an enhanced steric effect at the anode surface. This effect effectively hinders the contact between zinc metal and water molecules, consequently facilitating the uniform and controlled deposition of Zn2+. Furthermore, the combination between CPL and Zn2+ contributes to the optimization of solvation structures. Consequently, Zn/Zn batteries with CPL additives realized more than 2100 h stable cycling life under 1 mA cm-2 and 1 mAh cm-2. Moreover, Zn/Cu batteries with CPL additives achieved a reversible plating/stripping process for over 3000 cycles with high average CE of 99.4%. Besides, the assembled Zn/NH4V4O10 full batteries using electrolyte of ZnSO4/CPL also exhibited excellent cyclic performance. The batteries yielded 77.1 mAh g- 1 under the current density of 5 A g-1 after 1000 cycles. CPL demonstrates significant potential as a cost-effective and multifunctional electrolyte additive for achieving stable and reliable AZIBs.