Ion-Sieving Separator\nFunctionalized by Natural Mineral\nCoating toward Ultrastable Zn Metal Anodes

Aqueous zinc-ion batteries (AZIBs) exhibit promising\nprospects\nin becoming large-scale energy storage systems due to environmental\nfriendliness, high security, and low cost. However, the growth of\nZn dendrites and side reactions remain heady obstacles for the practical\napplication of AZIBs. To solve these challenges, a functionalized\nJanus separator is successfully constructed by coating halloysite\nnanotubes (HNTs) on glass fiber (GF). Impressively, the different\nelectronegativity on the inner and outer surfaces of HNTs endows the\nHNT-GF separator with ion-sieving property, leading to a significantly\nhigh transference number of Zn<sup>2+</sup> (<i>t</i><sub>Zn<sup>2+</sup></sub> = 0.71). Meanwhile, the HNT-GF separator works\nas an interfacial ion comb to regular Zn<sup>2+</sup> flux and realizes\nmultisite progressive nucleation, bringing decreased nucleation overpotential\nand uniform Zn<sup>2+</sup> deposition. Consequently, the HNT-GF separator\nenables the Zn anode to display an ultralong plating/stripping life\nof 3000 h and high rate tolerance with a stable long cycle life even\nunder a density of 50 mA cm<sup>–2</sup>. Moreover, the Zn∥HNT‐GF∥MnO2 full cell represents an ultrastable cycling\nstability with a high capacity retention of 93.4% even after 1000\ncycles at a current density of 2 A g<sup>–1</sup>. This work\nprovides a convenient method for the separator modification of AZIBs.