Engineering Fluorine-rich Double Protective Layer on Zn Anode for Highly Reversible Aqueous Zinc-ion Batteries

Abstract

The high thermodynamic instability and side reactions of Zn-metal anode (ZMA), especially at high current densities, greatly impede the commercialization of aqueous zinc-ion batteries (AZIBs). Herein, a fluorine-rich double protective layer strategy is proposed to obtain the high reversibility of AZIBs through the introduction of a versatile tetradecafluorononane-1,9-diol (TDFND) additive in aqueous electrolyte. TDFND molecule with large adsorption energy (-1.51 eV) preferentially absorbs on the Zn anode surface to form a Zn(OR)₂ ^- (R=-CH₂ -(CF₂ )₇ -CH₂ -) cross-linking complex network, which balances space electric field and controls the Zn²⁺ ion flux, thus enabling the uniform and compact deposition of Zn (002) crystal planes. Meanwhile, TDFND with low Lowest unoccupied molecular orbital (LUMO, 0.10 eV) energy level is priorly decomposed to regulate the interfacial chemistry of ZMA by building a ZnF₂ -rich solid electrode/electrolyte interface (SEI) layer. It is found that a 14 nm-thick SEI layer delivers excellent structural integrity to suppress parasitic reactions by blocking the direct contact of active water and ZMA. Consequently, the Zn electrode exhibits a superior cycling life over 430 h at 10 mA cm^-2 and a high average Coulombic efficiency of 99.8 % at 5 mA cm^-2 . Furthermore, a 68 mAh pouch cell delivers 80.3 % capacity retention for 1000 cycles.

Keywords: Cross-Linking Network; Solid-Electrolyte Interface; Zinc Anode; Zinc-Ion Battery; ZnF2.