Deciphering the chain length effect of organic additives on Zn reversibility

The practical deployment of zinc (Zn) metal anodes is severely hindered by uncontrolled dendrite growth and parasitic side reactions. Although organic additives can alleviate these issues, the fundamental relationship between their molecular structure and Zn deposition/stripping reversibility remains inadequately understood. Herein, a homologous series of amide additives is employed to establish the effect of molecular chain length on Zn reversibility. Complementary theoretical and experimental analyses reveal that alkyl chain extension increases the electron density of the carbonyl oxygen and strengthens Zn²⁺–amide coordination, thereby reorganizing the primary solvation sheath toward enhanced amide coordination. This regulation generates a dual effect: stronger coordination raises the nucleation overpotential and promotes dense, uniform Zn nucleation, while reduced interfacial water activity suppresses hydrogen evolution and corrosion reactions. Consequently, the optimized amides electrolyte delivers an average Coulombic efficiency of 99.6% and enables stable Zn||Zn cycling for over 900 h at 40 mA·cm⁻² and 25 mAh·cm⁻², corresponding to approximately 75.8% Zn utilization. Zn||VS₂ full cells retain 87.9% of their initial capacity after 1000 cycles. Notably, the same chain length-dependent enhancement is reproduced in carbonate additives, establishing molecular chain engineering as a transferable strategy for highly reversible Zn metal anodes.