Unidirectional Ion Sieve Enabling High-Flux and Reversible Zinc Anodes

Abstract

The longevity of aqueous batteries after scaling up is largely restricted by metal anodes (Zn, Al, and Mg). Parasitic reactions and uncontrolled dendrites dominate failure modes, especially at high current densities. To fully improve its reversibility, tailored surface chemistry and well-designed ion transport channels are simultaneously demanded. Here, inspired by the reticulated structure of the sea urchin shell, an aligned porous coating assembled from graphene oxide and sodium alginate is anchored on zinc anodes, termed a unidirectional ion sieve. As revealed by multiscale modeling and tests, this biomimetic layer produces a high surface area, creating low-tortuosity channels that greatly enhance transport kinetics and uniform distribution of ions. The introduction of an ion-conductive natural polymer enables a well-tuned hydration structure and ion selectivity, greatly alleviating aqueous side reactions. With the structural-functional integrity design, the decorated symmetrical cell presents reversible cycling for 1600 h, with a greatly reduced nucleation potential of 21 mV and high Coulombic efficiency. Aided by the Distribution of Relaxation Time tool, different electrochemical processes are deconvoluted to understand respective mechanisms, thereby providing a referable strategy for product scaling. In the end, a 7Ah Zn||VO₂ pouch cell demonstrates stable cycling for over 500 cycles at 1 A·g^–1, with the capacity retention over 90%.