Zinc Citrate Chelate Derivative-Modified Sodium Alginate Hydrogel Electrolyte with Controlled Water Activity for Ultrastable Zn Anodes

Aqueous zinc-ion batteries often suffer from severe side reactions related to active water and dendrite growth. Herein, inspired by the hydrogen bond (H-bond) donor and positively charged group of zinc citrate chelate derivative (ZCCD), ZCCD serves as a modifier. A hydrogel electrolyte (HE) composed of sodium alginate (SA) and ZCCD (denoted as ZCCD-SA) is thus developed for ultrastable Zn anodes. The water activity in the bulk HE is lowered via increasing strong H-bonds. Simultaneously, ZCCD and SA, which are preferentially adsorbed on the Zn anode, not only decrease H 2 O adsorption to form a protective layer at the electrode/electrolyte interface, but more importantly, effectively capture coordinated H 2 O molecules during the Zn 2+ desolvation process. Consequently, the ZCCD-SA HE significantly inhibits side reactions on the Zn anode. Moreover, the strong intermolecular forces and 3D network of the ZCCD-SA HE enhance the mechanical strength and promote high ionic conductivity. As a result, the Zn anode in ZCCD-SA HE exhibits long-term cycling stability of 5700 h at 0.5 mA cm –2 and a high Coulombic efficiency of 99.6% at 1 mA cm –2 . Furthermore, the assembled Zn||I 2 full battery delivers excellent electrochemical performance, retaining a capacity of 87.8 mAh g –1 even after 8000 cycles.