Multifunctional Separator Design for Regulating Zn²⁺ Ion Flux and Zn Stripping in Anode-Less Zn Metal Batteries

Anode-less Zn metal batteries (ALZMBs) enhance energy density but require ultrahigh Coulombic efficiency for stability, which is hindered by side reactions and dendrite growth. A uniform Zn stripping process is essential for improving Coulombic efficiency, but the impact of separator design on Zn stripping remains unexplored. Herein, we propose a novel strategy to achieve the high reversibility of Zn plating and stripping by modifying the glass fiber (GF) separator with hydrated titanic acid (HTO), forming an HTO@GF separator. Experimental and theoretical calculations indicate that highly electronegative oxygen in HTO promotes electron loss from Zn metal and converts it into Zn²⁺, thereby modulating the Zn stripping process. The HTO exhibits strong water adsorption capability, facilitating Zn²⁺ desolvation, while its layered architecture provides abundant diffusion pathways for Zn²⁺. Consequently, Zn||Cu cells maintain 99.78% CE over 1500 cycles, and anode-less Cu||NaV₃O₈·1.5H₂O full cells operate for 800 cycles when using the HTO@GF separator.