Boosting the Kinetics and Stability of Zn Anodes in Aqueous Electrolytes with Supramolecular Cyclodextrin Additives

The hydrophobic internal cavity and hydrophilic external surface of cyclodextrins (CDs) render promising electrochemical applications. Here, we report a comparative and mechanistic study on the use of CD molecules (α-, β-, and γ-CD) as electrolyte additives for rechargeable Zn batteries. The addition of α-CD in aqueous ZnSO₄ solution reduces nucleation overpotential and activation energy of Zn plating and suppresses H₂ generation. Computational, spectroscopic, and electrochemical studies reveal that α-CD preferentially adsorbs in parallel on the Zn surface via secondary hydroxyl groups, suppressing water-induced side reactions of hydrogen evolution and hydroxide sulfate formation. Additionally, the hydrophilic exterior surface of α-CD with intense electron density simultaneously facilitates Zn²⁺ deposition and alleviates Zn dendrite formation. A formulated 3 M ZnSO₄ + 10 mM α-CD electrolyte enables homogenous Zn plating/stripping (average Coulombic efficiency ∼ 99.90%) at 1 mA cm^-2 in Zn|Cu cells and a considerable capacity retention of 84.20% after 800 cycles in Zn|V₂O₅ full batteries. This study provides insight into the use of supramolecular macrocycles to modulate and enhance the interface stability and kinetics of metallic anodes for aqueous battery chemistry.