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

Abstract

A Zn2+-coordinated porphyrinic artificial solid-electrolyte interphase (alpha SEI) 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 alpha SEI layer was designed with zinc ions connecting porphyrinic building blocks to form two-dimensional clathrate sheets and stacking xy-plane sheets along the z-axis to allow N4 cages to align and form porphyrinic N4 channels for zinc transport. The [Zn]PP-4COO-(Zn) alpha SEI layer was Zn2+-conductive and structurally durable during repeated stripping/plating. Zinc ions traveled through the porphyrinic alpha SEI layer along the N4 channels via (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.