Vertically-oriented growth of MgMOF layer via heteroepitaxial guidance for highly stable magnesium-metal anode

Hybrid Li-Mg batteries (LMBs) have captured growing attention beyond lithium-ion batteries, however, the practical application of LMBs has still been blocked by the passivated layer on the Mg anode surface, as well as the nonuniform Mg2+ electrodeposition. Herein, we designed a vertically-oriented MgMOF layer on the surface of Mg foil, which functioned as the Mg2+ reservoir and guided the directional growth, via the heteroepitaxial growth strategy. It was an ingenious synergism of the lattice precise matching (lattice geometrical misfit less than 1%), magnesiophilic interface and electrical-field effect. The MgMOF layer was designed to improve the electrochemical kinetics of the Mg-electrolyte interface and guide the uniform Mg2+ electroplating/stripping under high current density. Remarkably, the MgMOF layer, with enriched Mg2+ affinity sites and the 1D aligned MOF channels, promoted the fast Mg2+ transportation and homogeneous Mg nucleation and growth. The MgMOF@Mg anode exhibited decreased Mg nucleation overpotential due to the protective MOF layer. The assembled MgMOF@Mg//MgMOF@Mg cell delivered elongated lifespan of 1200 cycles, even under the high current density of 8 mA cm−2 without short circuit. Impressively, the full cell, coupled with Mo6S8 cathode, displayed excellent cycling performance with capacity retention of 80.56 %, even after 14000 cycles at 50 C. The design concept shed fresh light for the rational design of MOF-based protective layer from the lattice geometrical perspective, which could be widely applied to other advanced metal batteries