Gradient solid electrolyte interphase exerted by robust hydrogel electrolyte-Zn interface and alkaloid additive enables reversible and durable Zn anodes

The advancement of aqueous Zn-ion energy storage systems is blocked by intractable dendrite growth and side reactions at the precarious Zn-electrolyte interface. To address these concerns, we herein propose an interface modulation strategy to construct a favorable solid electrolyte interphase (SEI) by developing a functional hydrogel electrolyte with zincophilic betaine (BT) additive. With the assistance of a well-bonded interface generated by the in-situ sol–gel transition of the hydrogel electrolyte, BT molecules preferentially adsorb on the Zn surface to reconstruct the electrical double layer and result in the formation of a hybrid SEI characterized by the organic-rich outer layer. This configuration effectively isolates water molecules from the Zn anode surface, curtailing water-related side reactions. Furthermore, Zn2+ ions are readily desolvated by adsorbed BT molecules and their derived outer organic interphase, and further diffuse uniformly on the electrode surface to achieve uniform deposition. Thanks to these favorable effects, the BT-containing hydrogel electrolyte endows Zn anodes with improved plating/stripping reversibility (average coulombic efficiency of 98.2 % over 1600 cycles for Zn//Cu cell) and stability (cycle life of 2400 h at 2 mA cm−2 for Zn//Zn cell). In addition, the resulting Zn-ion hybrid micro-capacitor shows excellent cyclability (83.7 % capacity retention after 12000 cycles) at 5 mA cm−2. This work would inspire the hydrogel electrolyte design to optimize the Zn-electrolyte interface for realizing durable and reversible Zn anodes and their derived energy storage systems.