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 (alpha-, beta-, and gamma-CD) as electrolyte additives for rechargeable Zn batteries. The addition of alpha-CD in aqueous ZnSO4 solution reduces nucleation overpotential and activation energy of Zn plating and suppresses H-2 generation. Computational, spectroscopic, and electrochemical studies reveal that alpha-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 alpha-CD with intense electron density simultaneously facilitates Zn2+ deposition and alleviates Zn dendrite formation. A formulated 3 M ZnSO4 + 10 mM alpha-CD electrolyte enables homogenous Zn plating/stripping (average Coulombic efficiency similar to 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.

Automated summary

This study demonstrates the potential of cyclodextrins (CDs) as electrolyte additives for rechargeable Zn batteries. The addition of alpha-CD improves the stability and kinetics of Zn plating and stripping by adsorbing on the Zn surface and suppressing water-induced side reactions. This finding provides insight into the use of supramolecular macrocycles for enhancing the performance of aqueous battery chemistry.