Dual role of hBN as an artificial solid-electrolyte interface layer for safe zinc metal anodes

Highly reversible and stable cycling of zinc metal anodes remains a challenge due to the undesirable side reaction of the hydrogen evolution reaction (HER) and dendrite formation. Herein, hexagonal boron nitride (hBN) with large area and continuous growth was developed and used as the artificial solid-electrolyte interface (SEI) coating, which plays two roles to protect the electrode surface by (1) mitigating the side reactions and (2) inducing the epitaxial electrodeposition of hexagonal close-packed (hcp) Zn to form the compact Zn structure aligned in (002) orientation. From the density functional theory (DFT) calculations, hBN exhibits a remarkably small lattice mismatch (4.1%) with the Zn (002) surface. Additionally, insignificant Zn binding energy of hBN (?0.20 eV) reveals a weak interaction between hBN and Zn atoms; therefore fewer seeding points are provided for generating Zn dendrites. In addition, the low surface energy of the hBN interface enhances the electrolyte wettability to the electrode-electrolyte interface, promoting smooth Zn plating. Consistently, highly horizontally aligned Zn metal deposition without dendrites and H₂ formation was visualized from an in situ optical cell. The symmetric cell shows stable cycling with a significantly smaller plating overpotential of 0.15 V over 300 cycles, while a full cell with an Al_xVOH cathode exhibits highly stable cycling over 50 cycles with a 73.6% capacity retention rate and improved rate capability.