Porphyrinic N₄ channels of zinc ions for the electrochemical reversibility of zinc plating/stripping

A Zn²⁺-coordinated porphyrinic artificial solid-electrolyte interphase (αSEI) layer, named [Zn]PP-4COO-(Zn), was developed to improve the reversibility of zinc metal plating/stripping in aqueous zinc-ion batteries (ZIBs). Inspired by nitrogen-terminating sites of biological molecules coordinating and transporting zinc in zinc metabolic processes, the αSEI layer was designed with zinc ions connecting porphyrinic building blocks to form two-dimensional clathrate sheets and stacking <i>xy</i>-plane sheets along the <i>z</i>-axis to allow N₄ cages to align and form porphyrinic N₄ channels for zinc transport. The [Zn]PP-4COO-(Zn) αSEI layer was Zn²⁺-conductive and structurally durable during repeated stripping/plating. Zinc ions traveled through the porphyrinic αSEI layer along the N₄ channels <i>via</i> (1) desolvation, (2) coordination to two nitrogens of the first clathrate sheet, (3) passing through distorted N₄ cages, (4) moving to inter-plane N₄ (two nitrogens from the first sheet and two nitrogens from the second sheet), (5) consecutive transport to next inter-plane N₄, and (6) metal nucleation on zinc metal foil during plating. Zinc ions coming from electrolytes along the N₄ channels were plated preferentially along the (002) plane, ensuring the non-dendritic growth of zinc metal for supporting plating/stripping reversibility to guarantee cycling durability. The porphyrinic N₄ zinc-ion channels kept the zinc symmetric cells healthy even after 1500 times repeated plating/stripping during 3000 h operation.