Highly Reversible Zn Metal Anode Stabilized by Dense and Anion-Derived Passivation Layer Obtained from Concentrated Hybrid Aqueous Electrolyte

Abstract

Zinc metal is considered a promising anode material for aqueous zinc ion batteries. However, it suffers from dendrite growth, corrosion, and low coulombic efficiency (CE) during plating/stripping. Herein, a concentrated hybrid (4 m Zn(CF3SO3)2 + 2 m LiClO4) aqueous electrolyte (CHAE) to overcome the challenges facing the Zn anode is reported. The developed electrolyte achieves dendrite-free Zn plating/stripping and obtains an excellent CE of ≈100%, surpassing the previously reported values. The combination of synchrotron-based in operando transmission X-ray microscopy, X-ray diffraction, and ex situ X-ray photoelectron spectroscopy analyses indicate that the denser, anion-derived passivation layer formed using the CHAE facilitates homogeneous current distribution and better prevents freshly deposited Zn from directly contacting the electrolyte than the looser, solvent-derived layers formed from a dilute hybrid aqueous electrolyte (DHAE). The beneficial effects of the CHAE on the compact, dense, and stable salt-anion-derived passivation layer can be attributed to its unique solvation structure, which suppresses the water-related side reactions and widens the electrochemical potential window. In the hybrid Zn||LiFePO4 configuration, the CHAE-based cell delivered a stable performance of CE >99% and capacity retention >90% after 285 cycles. In contrast, the DHAE-based cell exhibits capacity retention of <65% after 170 cycles.