Reshaping Li-Mg hybrid batteries: Epitaxial electrodeposition and spatial confinement on MgMOF substrates via the lattice-matching strategy

The emergence of Li-Mg hybrid batteries has been receiving attention, owing to their enhanced electrochemical kinetics and reduced overpotential. Nevertheless, the persistent challenge of uneven Mg electrodeposition remains a significant impediment to their practical integration. Herein, we developed an ingenious approach that centered around epitaxial electrocrystallization and meticulously controlled growth of magnesium crystals on a specialized MgMOF substrate. The chosen MgMOF substrate demonstrated a robust affinity for magnesium and showed minimal lattice misfit with Mg, establishing the crucial prerequisites for successful heteroepitaxial electrocrystallization. Moreover, the incorporation of periodic electric fields and successive nanochannels within the MgMOF structure created a spatially confined environment that considerably promoted uniform magnesium nucleation at the molecular scale. Taking inspiration from the "blockchain" concept prevalent in the realm of big data, we seamlessly integrated a conductive polypyrrole framework, acting as a connecting "chain," to interlink the "blocks" comprising the MgMOF cavities. This innovative design significantly amplified charge-transfer efficiency, thereby increasing overall electrochemical kinetics. The resulting architecture (MgMOF@PPy@CC) served as an exceptional host for heteroepitaxial Mg electrodeposition, showcasing remarkable electrostripping/plating kinetics and excellent cycling performance. Surprisingly, a symmetrical cell incorporating the MgMOF@PPy@CC electrode demonstrated impressive stability even under ultrahigh current density conditions (10 mA cm-2), maintaining operation for an extended 1200 h, surpassing previously reported benchmarks. Significantly, on coupling the MgMOF@PPy@CC anode with a Mo6S8 cathode, the assembled battery showed an extended lifespan of 10,000 cycles at 70 C, with an outstanding capacity retention of 96.23%. This study provides a fresh perspective on the rational design of epitaxial electrocrystallization driven by metal-organic framework (MOF) substrates, paving the way toward the advancement of cutting-edge batteries.