Functionalized Phosphonium Cations Enable Zinc Metal Reversibility in Aqueous Electrolytes

Aqueous rechargeable zinc metal batteries promise attractive advantages including safety, high volumetric energy density, and low cost; however, such benefits cannot be unlocked unless Zn reversibility meets stringent commercial viability. Herein, we report remarkable improvements on Zn reversibility in aqueous electrolytes when phosphonium-based cations are used to reshape interfacial structures and interphasial chemistries, particularly when their ligands contain an ether linkage. This novel aqueous electrolyte supports unprecedented Zn reversibility by showing dendrite-free Zn plating/stripping for over 6400 h at 0.5 mA cm^-2 , or over 280 h at 2.5 mA cm^-2 , with coulombic efficiency above 99 % even with 20 % Zn utilization per cycle. Excellent full cell performance is demonstrated with Na₂ V₆ O₁₆ ⋅1.63 H₂ O cathode, which cycles for 2000 times at 300 mA g^-1 . The microscopic characterization and modeling identify the mechanism of unique interphase chemistry from phosphonium and its functionalities as the key factors responsible for dictating reversible Zn chemistry.