Ultrastable Zn/Li hybrid ion batteries achieved by highly reversible Zn plating/stripping in ZnCl2-LiCl water-in-bisalt electrolytes

Zinc batteries are regarded as promising candidates for safe and cost-effective energy storage systems; however, their practical applications are still hindered by parasitic reactions and unstable zinc plating/stripping behavior. In this study, a ZnCl 2 -LiCl-acetonitrile water-in-bisalt electrolyte with a tailored solvation structure was developed at a molality ratio of 30-19-8. The incorporation of acetonitrile disrupts the hydrogen-bond network within the electrolyte, aiming to enhance the reversibility of zinc plating/stripping and improve the interfacial stability of Zn-Li hybrid-ion batteries. Raman spectroscopy reveals that at high salt concentrations, the coordination interactions of Zn 2+ /Li + with Cl - and acetonitrile are significantly strengthened, accompanied by disruption of the hydrogen-bond network and reduced water activity. The optimized high-concentration electrolyte exhibits highly reversible zinc plating/stripping behavior, achieving long-term stability over 2000 h in Zn//Zn symmetric cells and delivering average coulombic efficiencies above 99.9% after 4000 cycles in Zn//Cu and Zn//In asymmetric cells. In-situ optical microscopy and scanning electron microscopy observations further confirm the uniform and dense zinc deposition in the 30-19-8 electrolyte. When paired with high-voltage LiMn 2 O 4 (LMO) as the cathode, the Zn//LMO hybrid-ion battery maintains an average coulombic efficiency of 98.8% and a capacity retention of 50.8% after 10,000 cycles. Furthermore, the anode-free Cu//LMO hybrid-ion battery demonstrates an average coulombic efficiency of 99.13% along with excellent capacity retention. These results demonstrate that the rational design of water-in-bisalt electrolytes provides a promising strategy for developing high-performance Zn/Li hybrid-ion batteries.