In situ directly grown carboxylated UiO-66-infused separator as a comprehensive regulator of Zn solvation structure enabling dendrite- and corrosion-free Zn metal anode

Aqueous zinc ion batteries (AZIBs) are considered promising candidates owing to their inherent safety and low cost. However, the conventional glass fiber (GF) separator used in AZIBs suffers from poor physicochemical properties, leading to uncontrolled zinc (Zn) dendrite formation and undesirable side reactions. To address these limitations and enhance the electrochemical performance of AZIBs, a precisely designed functional separator is developed by incorporating UiO-66-(COOH)₂ into a poly(vinylidene fluoride) (PVDF) framework (U-PVDF) via a direct in situ growth method. This approach enables uniform distribution of UiO-66-(COOH)₂ both on the surface and within the PVDF backbone, without increasing separator thickness. Owing to the strong interaction between Zn²⁺ and the abundant carboxyl groups in UiO-66-(COOH)₂, the U-PVDF separator regulates the Zn²⁺ solvation structure toward a contact ion pair-dominated structure by reducing coordinated water molecules, which effectively mitigates water-induced parasitic reactions and promotes compact Zn deposition. Consequently, a Zn/Zn symmetric cell employing the U-PVDF separator demonstrates superior cycling stability over 1500 cycles without internal short-circuiting at a current density of 6 mA cm⁻² and an areal capacity of 2 mAh cm⁻². Moreover, Zn/NaV₃O₈·xH₂O (NVO) cell with the U-PVDF separator exhibits markedly improved cyclability and rate performance compared with those using conventional GF separator.