Regulating the solvation environment of hybrid electrolytes towards high-temperature zinc-ion storage

Abstract

Zinc-ion batteries (ZIBs) are being explored as a potential alternative to lithium-ion batteries owing to the growing demand for safer, more sustainable, cost-effective energy storage technologies. In such systems, electrolytes, as one of the key components, have a decisive impact on their electrochemical performance. However, Zn anodes in traditional aqueous electrolytes exhibit drawbacks such as severe hydrogen evolution reactions, Zn corrosion and passivation especially at high temperatures, leading to poor cycling performance of ZIBs. Herein, we designed and evaluated a series of hybrid electrolytes consisting of zinc tetrafluoroborate hydrate [Zn(BF4)2·xH2O] as the solute and various organic solvents [tetraglyme (G4), propylene carbonate, and dimethylformamide] for high-temperature ZIBs. Comparative analysis revealed that G4-based hybrid electrolytes exhibit a unique Zn2+ solvation structure primarily surrounded by organic solvent rather than H2O, which substantially reduces H2O-related side reactions and thus promotes more reversible Zn deposition than propylene carbonate-based and dimethylformamide-based hybrid electrolytes. The superiority of G4-based hybrid electrolyte is further confirmed by long stable cycling life of the corresponding Zn||Zn symmetric cell (> 350 h) and Zn-ion capacitor full cell (over 1,400 cycles with 90.7% capacity retention) at 60 °C.