Multivalent Ion-Conducting Metal- and Covalent- Organic Frameworks

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) offer uniquely tunable nanoporous architectures, and ionic groups can provide the additional hopping sites, rendering them promising ion conductors for multivalent-ion batteries (e.g., Zn²⁺, Mg²⁺, Ca²⁺, Al³⁺). This review first examines the unique structures and ion transport mechanisms, highlighting how framework flexibility and functionalization lower activation energies for bulky multivalent cations. We then outline structural design principles, including incorporation of ionic groups to maximize ionic conductivity. Key synthetic methods such as mechanical grinding, ball milling, reflux, hydrothermal/solvothermal, and interfacial synthesis are compared in terms of crystallinity, scalability, and environmental impact. Potential applications of MOF/COF as solid electrolytes, membranes, and interfacial coatings for multivalent batteries to improve cycle life. The future research directions are also proposed to enable MOF/COF materials as practical conductors in next-generation multivalent-ion energy storage systems.