Geometrical design of top-to-bottom magnesiophilicity-gradient host for reversible Mg-metal batteries

Abstract

Magnesium-metal batteries (MMBs) are promising candidates for large-scale energy-storage systems owing to their high volumetric capacity, low cost, and high level of safety. However, the problems of dendritic Mg deposition and its poor adhesion to a substrate remain unresolved. Herein, we first propose a unique geometrical design of a top-to-bottom magnesiophilicity-gradient 3D host for reversible MMBs. By systematically stacking three mesh layers with different Mg affinities, the 3D-Mg affinity controlled architecture (3D-MACA) can be simply fabricated. The bottom layer was designed to contain numerous nanofibers decorated with magnesiophilic Au seeds, which effectively guided the bottom-oriented Mg nucleation. In addition, the electrically insulated top layer could minimize the undesirable top-plating of Mg. As a result, 3D-MACA showed the lowest nucleation overpotential and highest cycle retention among the potential candidates. For evidence of bottom-oriented growth, ex-situ observation analysis of 3D-MACA was performed, and the geometrical effect was further investigated and explained by the theoretical 3D simulation. The proposed strategy may provide insight for future studies aimed at solving the prevailing issues for MMBs; in addition, the unique design can be extended to other metal battery systems.