High-Voltage and Super-Stable Aqueous Sodium-Zinc Hybrid Ion Batteries Enabled by Double Solvation Structures in Concentrated Electrolyte

Aqueous sodium-zinc hybrid ion batteries are attracting extensive attention due to high energy density, low cost, and environmental friendliness. Unfortunately, there are still some drawbacks associated with the low voltage and cycle performance degradation that limit their practical application. Here, a concentrated aqueous electrolyte with solvation-modulated Zn2+ is reported that reduces the hydrogen evolution reaction on the surface of Zn metal, avoiding the generation of ZnO and uneven deposition. Accordingly, the Zn anode exhibits 1600 h Zn plating/stripping and approximate to 99.96% Coulombic efficiency after 700 cycles. In addition, solvation-modulated Na+ promotes the excellent structural stability of zinc hexacyanoferrate (ZnHCF) due to the rhombohedral-rhombohedral rather than rhombohedral-cubic phase transition. A ZnHCF//Zn full cell delivers an average voltage of 1.76 V and 98% capacity retention after 2000 cycles at 5 C rates.

Automated summary

This study reports a method to improve the performance of aqueous sodium-zinc hybrid ion batteries by modulating the solvation of Zn2+ and Na+, successfully reducing hydrogen gas evolution and uneven zinc deposition, enhancing the battery's cycle life and efficiency.