Bidirectional Interface Protection of a Concentrated Electrolyte, Enabling High-Voltage and Long-Life Aqueous Zn Hybrid-Ion Batteries

Prussian blue analogues (PBAs) as a promising high-voltage cathode material for aqueous zinc-ion batteries (ZIBs) are usually subjected to an ephemeral lifespan and low Coulombic efficiency due to the irreversible phase change and high Zn2+ insertion potential. Besides, Zn dendrites, H2 evolution reaction, and corrosion derived from a Zn anode interface remain huge challenges. Given this, a highly stable zinc hexacyanoferrate (KZnHCF) cathode together with a mixed concentrated electrolyte is prepared to realize a high-voltage and long-life aqueous ZIB, in which the mixed concentrated electrolyte consisting of 30 m KFSI + 1 m Zn­(CF3SO3)2 possesses a unique Zn2+ solvation sheath (Zn­(CF3SO3)0.3(FSI)3.1(H2O)2.6) that can not only stabilize the cathode interface and improve the Coulombic efficiency but also fundamentally solve the Zn anode interface issues. As a result, the aqueous KZnHCF/Zn battery achieves an ultralong life over 3000 cycles without any capacity decay even under a high discharge voltage of 1.78 V (vs Zn2+/Zn). Such extraordinary performance represents significant progress in aqueous PBA-based ZIBs. This work shares guidance to improve the performance of aqueous ZIBs through optimizing the electrolyte in tuning the stable operation of the cathode and the zinc anode.