Synergistic regulation of the Zn ²⁺ solvation environment and interfacial stability using a rhodamine 6G additive in aqueous zinc ion batteries

In response to the challenges faced by zinc anodes in aqueous zinc-ion batteries, such as dendrite growth and interface corrosion, this study introduces rhodamine 6G (R6G) as an electrolyte additive. The collective evidence from DFT calculations and experimental characterization studies-specifically, the binding energy (-15.11 eV), the adsorption energy (-2.533 eV), and the HOMO-LUMO gap (1.102 eV)-reveals a dual-function mechanism: (1) polar groups (-NHCH₂CH₃ and -COOCH₂CH₃) preferentially replace the coordinated water molecules in the first solvation layer of Zn²⁺, reducing the desolvation energy barrier and (2) the rigid conjugated skeleton adsorbs on the zinc surface <i>via</i> π-Zn interactions, contributing to the formation of a protective organic-inorganic composite SEI film. As observed from the electrochemical testing results, the optimized R6G electrolyte enables Zn||Zn cells to undergo 1410 h of cycling at 0.5 mA cm^-2/0.5 mAh cm^-2 and 219 h at 5 mA cm^-2/5 mAh cm^-2. Meanwhile, the Zn||Cu cell achieves an average coulombic efficiency of 99.7% after 1200 cycles. The Zn||MnO₂ full cell exhibited a specific capacity of 152 mAh g^-1 after 1200 cycles at 1 A g^-1 with a capacity retention rate of 76.4%. Therefore, the "coordination substitution-interface film formation" synergistic model proposed in this study provides novel insights for the design of highly stable zinc anodes.