Cyclodextrin-Modified Hydrogel Electrolyte for Stable Zinc Anodes in Durable Zinc-Ion Hybrid Capacitors

The practical deployment of aqueous zinc-based energy storage devices is severely hampered by uncontrollable dendrite growth and parasitic reactions at the zinc anode interface. To address these challenges, this work proposes sulfobutyl ether-β-cyclodextrin (SBE-β-CD) as a multifunctional additive for high-performance quasi-solid-state zinc-ion hybrid capacitors (ZHCs). The SBE-β-CD molecule concurrently manipulates the hydrogen-bond network and ion transport properties within the hydrogel electrolyte. Its zincophilic sulfonate motifs establish efficient ion-conduction pathways, endowing the electrolyte with high ionic conductivity and an elevated Zn 2+ transference number. Simultaneously, the additive restructures the inherent hydrogen-bonding network, effectively suppressing water activity and associated side reactions. Furthermore, it regulates interfacial ion behaviors and guides preferentially oriented zinc deposition along the (002) crystallographic plane, thereby inhibiting dendrite formation and promoting a uniform plating morphology. As a result, the optimized electrolyte enables a Zn||Cu cell to achieve an exceptional average Coulombic efficiency of 99.5% over 800 cycles and a Zn||Zn symmetric cell to maintain stable operation for over 820 h. The assembled ZHC demonstrates remarkable cycling durability with 85.4% capacity retention after 21,700 cycles, alongside feasibility for powering electronics. This molecular engineering strategy offers a versatile and promising pathway for developing flexible and safe zinc-based energy storage systems.